Slonik


A battle-tested PostgreSQL client with strict types, detailed logging and assertions.

!Tailing Slonik logs

(The above GIF shows Slonik producing query logs. Slonik produces logs using Roarr. Logs include stack trace of the actual query invocation location and values used to execute the query.)

Sponsors

If you value my work and want to see Slonik and many other of my Open-Source projects to be continuously improved, then please consider becoming a patron:


Principles

* Promotes writing raw SQL.
* Discourages ad-hoc dynamic generation of SQL.

Read: Stop using Knex.js

Note: Using this project does not require TypeScript. It is a regular ES6 module. Ignore the type definitions used in the documentation if you do not use a type system.

Features

* Assertions and type safety.
* Connection mocking.
* Safe connection handling.
* Safe transaction handling.
* Safe value interpolation.
* Transaction nesting.
* Transaction retrying
* Detailed logging.
* Asynchronous stack trace resolution.
* Middlewares.
* Mapped errors.
* ESLint plugin.

Contents

* Slonik
* Sponsors
* Principles
* Features
* Contents
* About Slonik
* Battle-Tested
* Origin of the name
* Repeating code patterns and type safety
* Protecting against unsafe connection handling
* Protecting against unsafe transaction handling
* Protecting against unsafe value interpolation
* Documentation
* Usage
* Create connection
* End connection pool
* Describing the current state of the connection pool
* API
* Default configuration
* Using native libpq bindings
* Checking out a client from the connection pool
* Mocking Slonik
* How are they different?
* pg vs slonik
* pg-promise vs slonik
* Type parsers
* Built-in type parsers
* Interceptors
* Interceptor methods
* Community interceptors
* Recipes
* Inserting large number of rows
* Routing queries to different connections
* sql tag
* Value placeholders
* Tagged template literals
* Manually constructing the query
* Nesting sql
* Query building
* sql.array
* sql.binary
* sql.identifier
* sql.json
* sql.join
* sql.unnest
* Query methods
* any
* anyFirst
* exists
* copyFromBinary
* many
* manyFirst
* maybeOne
* maybeOneFirst
* one
* oneFirst
* query
* stream
* transaction
* Error handling
* Original node-postgres error
* Handling BackendTerminatedError
* Handling CheckIntegrityConstraintViolationError
* Handling ConnectionError
* Handling DataIntegrityError
* Handling ForeignKeyIntegrityConstraintViolationError
* Handling NotFoundError
* Handling NotNullIntegrityConstraintViolationError
* Handling StatementCancelledError
* Handling StatementTimeoutError
* Handling UniqueIntegrityConstraintViolationError
* Types
* Debugging
* Logging
* Capture stack trace
* Syntax Highlighting
* Atom Syntax Highlighting Plugin
* VS Code Syntax Highlighting Extension

About Slonik

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Slonik began as a collection of utilities designed for working with node-postgres. We continue to use node-postgres as it provides a robust foundation for interacting with PostgreSQL. However, what once was a collection of utilities has since grown into a framework that abstracts repeating code patterns, protects against unsafe connection handling and value interpolation, and provides rich debugging experience.

Slonik has been battle-tested with large data volumes and queries ranging from simple CRUD operations to data-warehousing needs.

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!Slonik

The name of the elephant depicted in the official PostgreSQL logo is Slonik. The name itself is derived from the Russian word for "little elephant".

Read: The History of Slonik, the PostgreSQL Elephant Logo

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Among the primary reasons for developing Slonik, was the motivation to reduce the repeating code patterns and add a level of type safety. This is primarily achieved through the methods such as one, many, etc. But what is the issue? It is best illustrated with an example.

Suppose the requirement is to write a method that retrieves a resource ID given values defining (what we assume to be) a unique constraint. If we did not have the aforementioned convenience methods available, then it would need to be written as:

``js
import {
sql
} from 'slonik';
import type {
DatabaseConnectionType
} from 'slonik';

type DatabaseRecordIdType = number;

const getFooIdByBar = async (connection: DatabaseConnectionType, bar: string): Promise => {
const fooResult = await connection.query(sql
SELECT id
FROM foo
WHERE bar = ${bar}
);

if (fooResult.rowCount === 0) {
throw new Error('Resource not found.');
}

if (fooResult.rowCount > 1) {
throw new Error('Data integrity constraint violation.');
}

return fooResult[0].id;
};

`

oneFirst method abstracts all of the above logic into:

`js
const getFooIdByBar = (connection: DatabaseConnectionType, bar: string): Promise => {
return connection.oneFirst(sql
SELECT id
FROM foo
WHERE bar = ${bar}
);
};

`

oneFirst throws:

* NotFoundError if query returns no rows
* DataIntegrityError if query returns multiple rows
* DataIntegrityError if query returns multiple columns

This becomes particularly important when writing routines where multiple queries depend on the previous result. Using methods with inbuilt assertions ensures that in case of an error, the error points to the original source of the problem. In contrast, unless assertions for all possible outcomes are typed out as in the previous example, the unexpected result of the query will be fed to the next operation. If you are lucky, the next operation will simply break; if you are unlucky, you are risking data corruption and hard to locate bugs.

Furthermore, using methods that guarantee the shape of the results, allows us to leverage static type checking and catch some of the errors even before they executing the code, e.g.

`js
const fooId = await connection.many(sql
SELECT id
FROM foo
WHERE bar = ${bar}
);

await connection.query(sql
DELETE FROM baz
WHERE foo_id = ${fooId}
);

`

Static type check of the above example will produce a warning as the fooId is guaranteed to be an array and binding of the last query is expecting a primitive value.

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Slonik only allows to check out a connection for the duration of the promise routine supplied to the pool#connect() method.

The primary reason for implementing _only_ this connection pooling method is because the alternative is inherently unsafe, e.g.

`js
// Note: This example is using unsupported API.

const main = async () => {
const connection = await pool.connect();

await connection.query(sqlSELECT foo());

await connection.release();
};

`

In this example, if SELECT foo() produces an error, then connection is never released, i.e. the connection remains to hang.

A fix to the above is to ensure that connection#release() is always called, i.e.

`js
// Note: This example is using unsupported API.

const main = async () => {
const connection = await pool.connect();

let lastExecutionResult;

try {
lastExecutionResult = await connection.query(sqlSELECT foo());
} finally {
await connection.release();
}

return lastExecutionResult;
};

`

Slonik abstracts the latter pattern into pool#connect() method.

`js
const main = () => {
return pool.connect((connection) => {
return connection.query(sqlSELECT foo());
});
};

`

Connection is always released back to the pool after the promise produced by the function supplied to connect() method is either resolved or rejected.

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Just like in the unsafe connection handling described above, Slonik only allows to create a transaction for the duration of the promise routine supplied to the connection#transaction() method.

`js
connection.transaction(async (transactionConnection) => {
await transactionConnection.query(sqlINSERT INTO foo (bar) VALUES ('baz'));
await transactionConnection.query(sqlINSERT INTO qux (quux) VALUES ('quuz'));
});

`

This pattern ensures that the transaction is either committed or aborted the moment the promise is either resolved or rejected.

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SQL injections are one of the most well known attack vectors. Some of the biggest data leaks were the consequence of improper user-input handling. In general, SQL injections are easily preventable by using parameterization and by restricting database permissions, e.g.

`js
// Note: This example is using unsupported API.

connection.query('SELECT $1', [
userInput
]);

`

In this example, the query text (SELECT $1) and parameters (value of the userInput) are passed to the PostgreSQL server where the parameters are safely substituted into the query. This is a safe way to execute a query using user-input.

The vulnerabilities appear when developers cut corners or when they do not know about parameterization, i.e. there is a risk that someone will instead write:

`js
// Note: This example is using unsupported API.

connection.query('SELECT \'' + userInput + '\'');

`

As evident by the history of the data leaks, this happens more often than anyone would like to admit. This is especially a big risk in Node.js community, where predominant number of developers are coming from frontend and have not had training working with RDBMSes. Therefore, one of the key selling points of Slonik is that it adds multiple layers of protection to prevent unsafe handling of user-input.

To begin with, Slonik does not allow to run plain-text queries.

`js
connection.query('SELECT 1');

`

The above invocation would produce an error:

> TypeError: Query must be constructed using sql tagged template literal.

This means that the only way to run a query is by constructing it using sql tagged template literal, e.g.

`js
connection.query(sqlSELECT 1);

`

To add a parameter to the query, user must use template literal placeholders, e.g.

`js
connection.query(sqlSELECT ${userInput});

`

Slonik takes over from here and constructs a query with value bindings, and sends the resulting query text and parameters to the PostgreSQL. As sql tagged template literal is the only way to execute the query, it adds a strong layer of protection against accidental unsafe user-input handling due to limited knowledge of the SQL client API.

As Slonik restricts user's ability to generate and execute dynamic SQL, it provides helper functions used to generate fragments of the query and the corresponding value bindings, e.g. sql.identifier, sql.join and sql.unnest. These methods generate tokens that the query executor interprets to construct a safe query, e.g.

`js
connection.query(sql
SELECT ${sql.identifier(['foo', 'a'])}
FROM (
VALUES
(
${sql.join(
[
sql.join(['a1', 'b1', 'c1'], sql, ),
sql.join(['a2', 'b2', 'c2'], sql, )
],
sql), (
)}
)
) foo(a, b, c)
WHERE foo.b IN (${sql.join(['c1', 'a2'], sql, )})
);

`

This (contrived) example generates a query equivalent to:

`sql
SELECT "foo"."a"
FROM (
VALUES
($1, $2, $3),
($4, $5, $6)
) foo(a, b, c)
WHERE foo.b IN ($7, $8)

`

That is executed with the parameters provided by the user.

To sum up, Slonik is designed to prevent accidental creation of queries vulnerable to SQL injections.

Documentation

Usage

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Use createPool to create a connection pool, e.g.

`js
import {
createPool,
} from 'slonik';

const pool = createPool('postgres://');

`

Instance of Slonik connection pool can be then used to create a new connection, e.g.

`js
pool.connect(async (connection) => {
await connection.query(sqlSELECT 1);
});

`

The connection will be kept alive until the promise resolves (the result of the method supplied to connect()).

Refer to query method documentation to learn about the connection methods.

If you do not require having a persistent connection to the same backend, then you can directly use pool to run queries, e.g.

`js
pool.query(sqlSELECT 1);

`

Beware that in the latter example, the connection picked to execute the query is a random connection from the connection pool, i.e. using the latter method (without explicit connect()) does not guarantee that multiple queries will refer to the same backend.

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Use pool.end() to end idle connections and prevent creation of new connections.

The result of pool.end() is a promise that is resolved when all connections are ended.

`js
import {
createPool,
sql,
} from 'slonik';

const pool = createPool('postgres://');

const main = async () => {
await pool.query(sql
SELECT 1
);

await pool.end();
};

main();

`

Note: pool.end() does not terminate active connections/ transactions.

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Use pool.getPoolState() to find out if pool is alive and how many connections are active and idle, and how many clients are waiting for a connection.

`js
import {
createPool,
sql,
} from 'slonik';

const pool = createPool('postgres://');

const main = async () => {
pool.getPoolState();

// {
// activeConnectionCount: 0,
// ended: false,
// idleConnectionCount: 0,
// waitingClientCount: 0,
// }

await pool.connect(() => {
pool.getPoolState();

// {
// activeConnectionCount: 1,
// ended: false,
// idleConnectionCount: 0,
// waitingClientCount: 0,
// }
});

pool.getPoolState();

// {
// activeConnectionCount: 0,
// ended: false,
// idleConnectionCount: 1,
// waitingClientCount: 0,
// }

await pool.end();

pool.getPoolState();

// {
// activeConnectionCount: 0,
// ended: true,
// idleConnectionCount: 0,
// waitingClientCount: 0,
// }
};

main();

`

Note: pool.end() does not terminate active connections/ transactions.

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`js
/**
* @param connectionUri PostgreSQL Connection URI.
*/
createPool(
connectionUri: string,
clientConfiguration: ClientConfigurationType
): DatabasePoolType;

/**
* @property captureStackTrace Dictates whether to capture stack trace before executing query. Middlewares access stack trace through query execution context. (Default: true)
* @property connectionRetryLimit Number of times to retry establishing a new connection. (Default: 3)
* @property connectionTimeout Timeout (in milliseconds) after which an error is raised if connection cannot cannot be established. (Default: 5000)
* @property idleInTransactionSessionTimeout Timeout (in milliseconds) after which idle clients are closed. Use 'DISABLE_TIMEOUT' constant to disable the timeout. (Default: 60000)
* @property idleTimeout Timeout (in milliseconds) after which idle clients are closed. Use 'DISABLE_TIMEOUT' constant to disable the timeout. (Default: 5000)
* @property interceptors An array of Slonik interceptors.
* @property maximumPoolSize Do not allow more than this many connections. Use 'DISABLE_TIMEOUT' constant to disable the timeout. (Default: 10)
* @property preferNativeBindings Uses libpq bindings when pg-native module is installed. (Default: true)
* @property statementTimeout Timeout (in milliseconds) after which database is instructed to abort the query. Use 'DISABLE_TIMEOUT' constant to disable the timeout. (Default: 60000)
* @property transactionRetryLimit Number of times a transaction failing with Transaction Rollback class error is retried. (Default: 5)
* @property typeParsers An array of Slonik type parsers.
*/
type ClientConfigurationInputType = {|
+captureStackTrace?: boolean,
+connectionRetryLimit?: number,
+connectionTimeout?: number | 'DISABLE_TIMEOUT',
+idleInTransactionSessionTimeout?: number | 'DISABLE_TIMEOUT',
+idleTimeout?: number | 'DISABLE_TIMEOUT',
+interceptors?: $ReadOnlyArray,
+maximumPoolSize?: number,
+preferNativeBindings?: boolean,
+statementTimeout?: number | 'DISABLE_TIMEOUT',
+transactionRetryLimit?: number,
+typeParsers?: $ReadOnlyArray,
|};

`

Example:

`js
import {
createPool
} from 'slonik';

const pool = createPool('postgres://');

await pool.query(sqlSELECT 1);

`

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#### Default interceptors

None.

Check out slonik-interceptor-preset for an opinionated collection of interceptors.


#### Default type parsers

These type parsers are enabled by default:

|Type name|Implementation|
|---|---|
|date|Produces a literal date as a string (format: YYYY-MM-DD).|
|int8|Produces an integer.|
|interval|Produces interval in seconds (integer).|
|numeric|Produces a float.|
|timestamp|Produces a unix timestamp (in milliseconds).|
|timestamptz|Produces a unix timestamp (in milliseconds).|

To disable the default type parsers, pass an empty array, e.g.

`js
createPool('postgres://', {
typeParsers: []
});

`

You can create default type parser collection using createTypeParserPreset, e.g.

`js
import {
createTypeParserPreset
} from 'slonik';

createPool('postgres://', {
typeParsers: [
...createTypeParserPreset()
]
});

`


#### Default timeouts

There are 4 types of configurable timeouts:

|Configuration|Description|Default|
|---|---|---|
|connectionTimeout|Timeout (in milliseconds) after which an error is raised if connection cannot cannot be established.|5000|
|idleInTransactionSessionTimeout|Timeout (in milliseconds) after which idle clients are closed. Use 'DISABLE_TIMEOUT' constant to disable the timeout.|60000|
|idleTimeout|Timeout (in milliseconds) after which idle clients are closed. Use 'DISABLE_TIMEOUT' constant to disable the timeout.|5000|
|statementTimeout|Timeout (in milliseconds) after which database is instructed to abort the query. Use 'DISABLE_TIMEOUT' constant to disable the timeout.|60000|

Slonik sets aggressive timeouts by default. These timeouts are designed to provide safe interface to the database. These timeouts might not work for all programs. If your program has long running statements, consider adjusting timeouts just for those statements instead of changing the defaults.

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In order to use native libpq PostgreSQL bindings install pg-native.

`bash
$ npm install pg-native

`

By default, Slonik uses native bindings when pg-native is installed. To use JavaScript bindings when pg-native is installed, configure preferNativeBindings: false.

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Slonik only allows to check out a connection for the duration of the promise routine supplied to the pool#connect() method.

`js
import {
createPool,
} from 'slonik';

const pool = createPool('postgres://localhost');

const result = await pool.connect(async (connection) => {
await connection.query(sqlSELECT 1);
await connection.query(sqlSELECT 2);

return 'foo';
});

result;
// 'foo'

`

Connection is released back to the pool after the promise produced by the function supplied to connect() method is either resolved or rejected.

Read: Protecting against unsafe connection handling

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Slonik provides a way to mock queries against the database.

* Use createMockPool to create a mock connection.
* Use createMockQueryResult to create a mock query result.

`js
import {
createMockPool,
createMockQueryResult,
} from 'slonik';

type OverridesType = {|
+query: (sql: string, values: $ReadOnlyArray,) => Promise>,
|};

createMockPool(overrides: OverridesType): DatabasePoolType;
createMockQueryResult(rows: $ReadOnlyArray): QueryResultType;

`

Example:

`js
import {
createMockPool,
createMockQueryResult,
} from 'slonik';

const pool = createMockPool({
query: async () => {
return createMockQueryResult([
{
foo: 'bar',
},
]);
},
});

await pool.connect(async (connection) => {
const results = await connection.query(sql
SELECT ${'foo'}
);
});

`

How are they different?

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pg is built intentionally to provide unopinionated, minimal abstraction and encourages use of other modules to implement convenience methods.

Slonik is built on top of pg and it provides convenience methods for building queries and querying data.

Work on pg began on Tue Sep 28 22:09:21 2010. It is authored by Brian Carlson.

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As the name suggests, pg-promise was originally built to enable use of pg module with promises (at the time, pg only supported Continuation Passing Style (CPS), i.e. callbacks). Since then pg-promise added features for connection/ transaction handling, a powerful query-formatting engine and a declarative approach to handling query results.

The primary difference between Slonik and pg-promise:

* Slonik does not allow to execute raw text queries. Slonik queries can only be constructed using sql tagged template literals. This design protects against unsafe value interpolation.
* Slonik implements interceptor API (middleware). Middlewares allow to modify connection handling, override queries and modify the query results. Example Slonik interceptors include field name transformation, query normalization and query benchmarking.

Note: Author of pg-promise has objected to the above claims. I have removed a difference that was clearly wrong. I maintain that the above two differences remain valid differences: even though pg-promise might have substitute functionality for variable interpolation and interceptors, it implements them in a way that does not provide the same benefits that Slonik provides, namely: guaranteed security and support for extending library functionality using multiple plugins.

Other differences are primarily in how the equivalent features are implemented, e.g.

|pg-promise|Slonik|
|---|---|
|Custom type formatting.|Not available in Slonik. The current proposal is to create an interceptor that would have access to the query fragment constructor.|
|formatting filters|Slonik tagged template value expressions to construct query fragments and bind parameter values.|
|Query files.|Use slonik-sql-tag-raw.|
|Tasks.|Use pool.connect.|
|Configurable transactions.|Not available in Slonik. Track this issue.|
|Events.|Use interceptors.|

When weighting which abstraction to use, it would be unfair not to consider that pg-promise is a mature project with dozens of contributors. Meanwhile, Slonik is a young project (started in March 2017) that until recently was developed without active community input. However, if you do support the unique features that Slonik adds, the opinionated API design, and are not afraid of adopting a technology in its young days, then I warmly invite you to adopt Slonik and become a contributor to what I intend to make the standard PostgreSQL client in the Node.js community.

Work on pg-promise began Wed Mar 4 02:00:34 2015. It is authored by Vitaly Tomilov.

Type parsers

Type parsers describe how to parse PostgreSQL types.

`js
type TypeParserType = {|
+name: string,
+parse: (value: string) => *
|};

`

Example:

`js
{
name: 'int8',
parse: (value) => {
return parseInt(value, 10);
}
}

`

Note: Unlike pg-types that uses OIDs to identify types, Slonik identifies types using their names.

Use this query to find type names:

`sql
SELECT
typname
FROM pg_type
ORDER BY typname ASC

`

Type parsers are configured using typeParsers client configuration.

Read: Default type parsers.

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|Type name|Implementation|Factory function name|
|---|---|---|
|date|Produces a literal date as a string (format: YYYY-MM-DD).|createDateTypeParser|
|int8|Produces an integer.|createBigintTypeParser|
|interval|Produces interval in seconds (integer).|createIntervalTypeParser|
|numeric|Produces a float.|createNumericTypeParser|
|timestamp|Produces a unix timestamp (in milliseconds).|createTimestampTypeParser|
|timestamptz|Produces a unix timestamp (in milliseconds).|createTimestampWithTimeZoneTypeParser|

Built-in type parsers can be created using the exported factory functions, e.g.

`js
import {
createTimestampTypeParser
} from 'slonik';

createTimestampTypeParser();

// {
// name: 'timestamp',
// parse: (value) => {
// return value === null ? value : Date.parse(value);
// }
// }

`

Interceptors

Functionality can be added to Slonik client by adding interceptors (middleware).

Interceptors are configured using client configuration, e.g.

`js
import {
createPool
} from 'slonik';

const interceptors = [];

const connection = createPool('postgres://', {
interceptors
});

`

Interceptors are executed in the order they are added.

Read: Default interceptors.

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Interceptor is an object that implements methods that can change the behaviour of the database client at different stages of the connection life-cycle

`js
type InterceptorType = {|
+afterPoolConnection?: (
connectionContext: ConnectionContextType,
connection: DatabasePoolConnectionType
) => MaybePromiseType,
+afterQueryExecution?: (
queryContext: QueryContextType,
query: QueryType,
result: QueryResultType
) => MaybePromiseType>,
+beforePoolConnection?: (
connectionContext: ConnectionContextType
) => MaybePromiseType,
+beforePoolConnectionRelease?: (
connectionContext: ConnectionContextType,
connection: DatabasePoolConnectionType
) => MaybePromiseType,
+beforeQueryExecution?: (
queryContext: QueryContextType,
query: QueryType
) => MaybePromiseType> | MaybePromiseType,
+beforeQueryResult?: (
queryContext: QueryContextType,
query: QueryType,
result: QueryResultType
) => MaybePromiseType,
+beforeTransformQuery?: (
queryContext: QueryContextType,
query: QueryType
) => Promise,
+queryExecutionError?: (
queryContext: QueryContextType,
query: QueryType,
error: SlonikError
) => MaybePromiseType,
+transformQuery?: (
queryContext: QueryContextType,
query: QueryType
) => QueryType,
+transformRow?: (
queryContext: QueryContextType,
query: QueryType,
row: QueryResultRowType,
fields: $ReadOnlyArray
) => QueryResultRowType
|};

`


#### afterPoolConnection

Executed after a connection is acquired from the connection pool (or a new connection is created), e.g.

`js
const pool = createPool('postgres://');

// Interceptor is executed here. ↓
pool.connect();

`


#### afterQueryExecution

Executed after query has been executed and before rows were transformed using transformRow.

Note: When query is executed using stream, then afterQuery is called with empty result set.


#### beforeQueryExecution

This function can optionally return a direct result of the query which will cause the actual query never to be executed.


#### beforeQueryResult

Executed just before the result is returned to the client.

Use this method to capture the result that will be returned to the client.


#### beforeTransformQuery

Executed before transformQuery. Use this interceptor to capture the original query (e.g. for logging purposes).


#### beforePoolConnectionRelease

Executed before connection is released back to the connection pool, e.g.

`js
const pool = await createPool('postgres://');

pool.connect(async () => {
await 1;

// Interceptor is executed here. ↓
});

`


#### queryExecutionError

Executed if query execution produces an error.

Use queryExecutionError to log and/ or re-throw another error.


#### transformQuery

Executed before beforeQueryExecution.

Transforms query.


#### transformRow

Executed for each row.

Transforms row.

Use transformRow to modify the query result.

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|Name|Description|
|---|---|
|slonik-interceptor-field-name-transformation|Transforms Slonik query result field names.|
|slonik-interceptor-query-benchmarking|Benchmarks Slonik queries.|
|slonik-interceptor-query-cache|Caches Slonik queries.|
|slonik-interceptor-query-logging|Logs Slonik queries.|
|slonik-interceptor-query-normalisation|Normalises Slonik queries.|

Check out slonik-interceptor-preset for an opinionated collection of interceptors.

Recipes

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Use sql.unnest to create a set of rows using unnest. Using the unnest approach requires only 1 variable per every column; values for each column are passed as an array, e.g.

`js
await connection.query(sql
INSERT INTO foo (bar, baz, qux)
SELECT *
FROM ${sql.unnest(
[
[1, 2, 3],
[4, 5, 6]
],
[
'int4',
'int4',
'int4'
]
)}
);

`

Produces:

`js
{
sql: 'INSERT INTO foo (bar, baz, qux) SELECT * FROM unnest($1::int4[], $2::int4[], $2::int4[])',
values: [
[
1,
4
],
[
2,
5
],
[
3,
6
]
]
}

`

Inserting data this way ensures that the query is stable and reduces the amount of time it takes to parse the query.

$3

If connection is initiated by a query (as opposed to a obtained explicitly using pool#connect()), then beforePoolConnection interceptor can be used to change the pool that will be used to execute the query, e.g.

`js
const slavePool = createPool('postgres://slave');
const masterPool = createPool('postgres://master', {
interceptors: [
{
beforePoolConnection: (connectionContext, pool) => {
if (connectionContext.query && connectionContext.query.sql.includes('SELECT')) {
return slavePool;
}

return pool;
}
}
]
});

// This query will use postgres://slave connection.
masterPool.query(sqlSELECT 1);

// This query will use postgres://master connection.
masterPool.query(sqlUPDATE 1);

`

sql tag

sql tag serves two purposes:

* It is used to construct queries with bound parameter values (see Value placeholders).
* It used to generate dynamic query fragments (see Query building).

sql tag can be imported from Slonik package:

`js
import {
sql
} from 'slonik';

`

Sometimes it may be desirable to construct a custom instance of sql tag. In those cases, you can use the createSqlTag factory, e.g.

`js
import {
createSqlTag
} from 'slonik';

/**
* @typedef SqlTagConfiguration
*/

/**
* @param {SqlTagConfiguration} configuration
*/
const sql = createSqlTag(configuration);

`

Value placeholders

$3

Slonik query methods can only be executed using sql tagged template literal, e.g.

`js
import {
sql
} from 'slonik'

connection.query(sql
SELECT 1
FROM foo
WHERE bar = ${'baz'}
);

`

The above is equivalent to evaluating:

`sql
SELECT 1
FROM foo
WHERE bar = $1

`

query with 'baz' value binding.

$3

Manually constructing queries is not allowed.

There is an internal mechanism that checks to see if query was created using sql tagged template literal, i.e.

`js
const query = {
sql: 'SELECT 1 FROM foo WHERE bar = $1',
type: 'SQL',
values: [
'baz'
]
};

connection.query(query);

`

Will result in an error:

> Query must be constructed using sql tagged template literal.

This is a security measure designed to prevent unsafe query execution.

Furthermore, a query object constructed using sql tagged template literal is frozen to prevent further manipulation.

$3

sql tagged template literals can be nested, e.g.

`js
const query0 = sqlSELECT ${'foo'} FROM bar;
const query1 = sqlSELECT ${'baz'} FROM (${query0});

`

Produces:

`js
{
sql: 'SELECT $1 FROM (SELECT $2 FROM bar)',
values: [
'baz',
'foo'
]
}

`

Query building

Queries are built using methods of the sql tagged template literal.

If this is your first time using Slonik, read Dynamically generating SQL queries using Node.js.

$3

`js
(
values: $ReadOnlyArray,
memberType: TypeNameIdentifierType | SqlTokenType
) => ArraySqlTokenType;

`

Creates an array value binding, e.g.

`js
await connection.query(sql
SELECT (${sql.array([1, 2, 3], 'int4')})
);

`

Produces:

`js
{
sql: 'SELECT $1::"int4"[]',
values: [
[
1,
2,
3
]
]
}

`


#### sql.array memberType

If memberType is a string (TypeNameIdentifierType), then it is treated as a type name identifier and will be quoted using double quotes, i.e. sql.array([1, 2, 3], 'int4') is equivalent to $1::"int4"[]. The implication is that keywords that are often used interchangeably with type names are not going to work, e.g. int4 is a type name identifier and will work. However, int is a keyword and will not work. You can either use type name identifiers or you can construct custom member using sql tag, e.g.

`js
await connection.query(sql
SELECT (${sql.array([1, 2, 3], sqlint[])})
);

`

Produces:

`js
{
sql: 'SELECT $1::int[]',
values: [
[
1,
2,
3
]
]
}

`


#### sql.array vs sql.join

Unlike sql.join, sql.array generates a stable query of a predictable length, i.e. regardless of the number of values in the array, the generated query remains the same:

* Having a stable query enables pg_stat_statements to aggregate all query execution statistics.
* Keeping the query length short reduces query parsing time.

Example:

`js
sqlSELECT id FROM foo WHERE id IN (${sql.join([1, 2, 3], sql, )});
sqlSELECT id FROM foo WHERE id NOT IN (${sql.join([1, 2, 3], sql, )});

`

Is equivalent to:

`js
sqlSELECT id FROM foo WHERE id = ANY(${sql.array([1, 2, 3], 'int4')});
sqlSELECT id FROM foo WHERE id != ALL(${sql.array([1, 2, 3], 'int4')});

`

Furthermore, unlike sql.join, sql.array can be used with an empty array of values. In short, sql.array should be preferred over sql.join when possible.

$3

`js
(
data: Buffer
) => BinarySqlTokenType;

`

Binds binary (bytea) data, e.g.

`js
await connection.query(sql
SELECT ${sql.binary(Buffer.from('foo'))}
);

`

Produces:

`js
{
sql: 'SELECT $1',
values: [
Buffer.from('foo')
]
}

`

$3

`js
(
names: $ReadOnlyArray
) => IdentifierSqlTokenType;

`

Delimited identifiers are created by enclosing an arbitrary sequence of characters in double-quotes ("). To create create a delimited identifier, create an sql tag function placeholder value using sql.identifier, e.g.

`js
sql
SELECT 1
FROM ${sql.identifier(['bar', 'baz'])}
;

`

Produces:

`js
{
sql: 'SELECT 1 FROM "bar"."baz"',
values: []
}

`

$3

`js
(
value: SerializableValueType
) => JsonSqlTokenType;

`

Serializes value and binds it as a JSON string literal, e.g.

`js
await connection.query(sql
SELECT (${sql.json([1, 2, 3])})
);

`

Produces:

`js
{
sql: 'SELECT $1',
values: [
'[1,2,3]'
]
}

`


#### Difference from JSON.stringify

|Input|sql.json|JSON.stringify|
|---|---|---|
|undefined|Throws InvalidInputError error.|undefined|
|null|null|"null" (string literal)|

$3

`js
(
members: $ReadOnlyArray,
glue: SqlTokenType
) => ListSqlTokenType;

`

Concatenates SQL expressions using glue separator, e.g.

`js
await connection.query(sql
SELECT ${sql.join([1, 2, 3], sql, )}
);

`

Produces:

`js
{
sql: 'SELECT $1, $2, $3',
values: [
1,
2,
3
]
}

`

sql.join is the primary building block for most of the SQL, e.g.

Boolean expressions:

`js
sql
SELECT ${sql.join([1, 2], sql AND )}

// SELECT $1 AND $2

`

Tuple:

`js
sql
SELECT (${sql.join([1, 2], sql, )})

// SELECT ($1, $2)

`

Tuple list:

`js
sql
SELECT ${sql.join(
[
sql(${sql.join([1, 2], sql, )}),
sql(${sql.join([3, 4], sql, )}),
],
sql,
)}

// SELECT ($1, $2), ($3, $4)

`

$3

`js
(
tuples: $ReadOnlyArray<$ReadOnlyArray>,
columnTypes: $ReadOnlyArray
): UnnestSqlTokenType;

`

Creates an unnest expressions, e.g.

`js
await connection.query(sql
SELECT bar, baz
FROM ${sql.unnest(
[
[1, 'foo'],
[2, 'bar']
],
[
'int4',
'text'
]
)} AS foo(bar, baz)
);

`

Produces:

`js
{
sql: 'SELECT bar, baz FROM unnest($1::int4[], $2::text[]) AS foo(bar, baz)',
values: [
[
1,
2
],
[
'foo',
'bar'
]
]
}

`

Query methods

$3

Returns result rows.

Example:

`js
const rows = await connection.any(sqlSELECT foo);

`

#any is similar to #query except that it returns rows without fields information.

$3

Returns value of the first column of every row in the result set.

* Throws DataIntegrityError if query returns multiple columns.

Example:

`js
const fooValues = await connection.anyFirst(sqlSELECT foo);

`

$3

Returns a boolean value indicating whether query produces results.

The query that is passed to this function is wrapped in SELECT exists() prior to it getting executed, i.e.

`js
pool.exists(sql
SELECT LIMIT 1
)

`

is equivalent to:

`js
pool.oneFirst(sql
SELECT exists(
SELECT LIMIT 1
)
)

`

$3

`js
(
streamQuery: TaggedTemplateLiteralInvocationType,
tupleList: $ReadOnlyArray<$ReadOnlyArray>,
columnTypes: $ReadOnlyArray
) => Promise;

`

Copies from a binary stream.

The binary stream is constructed using user supplied tupleList and columnTypes values.

Example:

`js
const tupleList = [
[
1,
'baz'
],
[
2,
'baz'
]
];

const columnTypes = [
'int4',
'text'
];

await connection.copyFromBinary(
sql
COPY foo
(
id,
baz
)
FROM STDIN BINARY
,
tupleList,
columnTypes
);

`


#### Limitations

* Tuples cannot contain NULL values.


#### Implementation notes

copyFromBinary implementation is designed to minimize the query execution time at the cost of increased script memory usage and execution time. This is achieved by separating data encoding from feeding data to PostgreSQL, i.e. all data passed to copyFromBinary is first encoded and then fed to PostgreSQL (contrast this to using a stream with encoding transformation to feed data to PostgreSQL).


#### Related documentation

* COPY documentation

$3

Returns result rows.

* Throws NotFoundError if query returns no rows.

Example:

`js
const rows = await connection.many(sqlSELECT foo);

`

$3

Returns value of the first column of every row in the result set.

* Throws NotFoundError if query returns no rows.
* Throws DataIntegrityError if query returns multiple columns.

Example:

`js
const fooValues = await connection.many(sqlSELECT foo);

`

$3

Selects the first row from the result.

* Returns null if row is not found.
* Throws DataIntegrityError if query returns multiple rows.

Example:

`js
const row = await connection.maybeOne(sqlSELECT foo);

// row.foo is the result of the foo column value of the first row.

`

$3

Returns value of the first column from the first row.

* Returns null if row is not found.
* Throws DataIntegrityError if query returns multiple rows.
* Throws DataIntegrityError if query returns multiple columns.

Example:

`js
const foo = await connection.maybeOneFirst(sqlSELECT foo);

// foo is the result of the foo column value of the first row.

`

$3

Selects the first row from the result.

* Throws NotFoundError if query returns no rows.
* Throws DataIntegrityError if query returns multiple rows.

Example:

`js
const row = await connection.one(sqlSELECT foo);

// row.foo is the result of the foo column value of the first row.

`

> Note:
>
> I've been asked "What makes this different from knex.js knex('foo').limit(1)?".
> knex('foo').limit(1) simply generates "SELECT * FROM foo LIMIT 1" query.
> knex is a query builder; it does not assert the value of the result.
> Slonik #one adds assertions about the result of the query.

$3

Returns value of the first column from the first row.

* Throws NotFoundError if query returns no rows.
* Throws DataIntegrityError if query returns multiple rows.
* Throws DataIntegrityError if query returns multiple columns.

Example:

`js
const foo = await connection.oneFirst(sqlSELECT foo);

// foo is the result of the foo column value of the first row.

`

$3

API and the result shape are equivalent to pg#query.

Example:

`js
await connection.query(sqlSELECT foo);

// {
// command: 'SELECT',
// fields: [],
// notices: [],
// rowCount: 1,
// rows: [
// {
// foo: 'bar'
// }
// ]
// }

`

$3

Streams query results.

Example:

`js
await connection.stream(sqlSELECT foo, (stream) => {
stream.on('data', (datum) => {
datum;
// {
// fields: [
// {
// name: 'foo',
// dataTypeId: 23,
// }
// ],
// row: {
// foo: 'bar'
// }
// }
});
});

`

Note: Implemented using pg-query-stream.

$3

transaction method is used wrap execution of queries in START TRANSACTION and COMMIT or ROLLBACK. COMMIT is called if the transaction handler returns a promise that resolves; ROLLBACK is called otherwise.

transaction method can be used together with createPool method. When used to create a transaction from an instance of a pool, a new connection is allocated for the duration of the transaction.

`js
const result = await connection.transaction(async (transactionConnection) => {
await transactionConnection.query(sqlINSERT INTO foo (bar) VALUES ('baz'));
await transactionConnection.query(sqlINSERT INTO qux (quux) VALUES ('corge'));

return 'FOO';
});

result === 'FOO';

`


#### Transaction nesting

Slonik uses SAVEPOINT to automatically nest transactions, e.g.

`js
await connection.transaction(async (t1) => {
await t1.query(sqlINSERT INTO foo (bar) VALUES ('baz'));

return t1.transaction((t2) => {
return t2.query(sqlINSERT INTO qux (quux) VALUES ('corge'));
});
});

`

is equivalent to:

`sql
START TRANSACTION;
INSERT INTO foo (bar) VALUES ('baz');
SAVEPOINT slonik_savepoint_1;
INSERT INTO qux (quux) VALUES ('corge');
COMMIT;

`

Slonik automatically rollsback to the last savepoint if a query belonging to a transaction results in an error, e.g.

`js
await connection.transaction(async (t1) => {
await t1.query(sqlINSERT INTO foo (bar) VALUES ('baz'));

try {
await t1.transaction(async (t2) => {
await t2.query(sqlINSERT INTO qux (quux) VALUES ('corge'));

return Promise.reject(new Error('foo'));
});
} catch (error) {

}
});

`

is equivalent to:

`sql
START TRANSACTION;
INSERT INTO foo (bar) VALUES ('baz');
SAVEPOINT slonik_savepoint_1;
INSERT INTO qux (quux) VALUES ('corge');
ROLLBACK TO SAVEPOINT slonik_savepoint_1;
COMMIT;

`

If error is unhandled, then the entire transaction is rolledback, e.g.

`js
await connection.transaction(async (t1) => {
await t1.query(sqlINSERT INTO foo (bar) VALUES ('baz'));

await t1.transaction(async (t2) => {
await t2.query(sqlINSERT INTO qux (quux) VALUES ('corge'));

await t1.transaction(async (t3) => {
await t3.query(sqlINSERT INTO uier (grault) VALUES ('garply'));

return Promise.reject(new Error('foo'));
});
});
});

`

is equivalent to:

`sql
START TRANSACTION;
INSERT INTO foo (bar) VALUES ('baz');
SAVEPOINT slonik_savepoint_1;
INSERT INTO qux (quux) VALUES ('corge');
SAVEPOINT slonik_savepoint_2;
INSERT INTO uier (grault) VALUES ('garply');
ROLLBACK TO SAVEPOINT slonik_savepoint_2;
ROLLBACK TO SAVEPOINT slonik_savepoint_1;
ROLLBACK;

`


#### Transaction retrying

Transactions that are failing with Transaction Rollback class errors are automatically retried.

A failing transaction will be rolled back and all queries up to the failing query will be replayed.

How many times a transaction is retried is controlled using transactionRetryLimit configuration (default: 5).

Error handling

All Slonik errors extend from SlonikError, i.e. You can catch Slonik specific errors using the following logic.

`js
import {
SlonikError
} from 'slonik';

try {
await query();
} catch (error) {
if (error instanceof SlonikError) {
// This error is thrown by Slonik.
}
}

`

$3

When error originates from node-postgres, the original error is available under originalError property.

This propery is exposed for debugging purposes only. Do not use it for conditional checks – it can change.

If you require to extract meta-data about a specific type of error (e.g. contraint violation name), raise a GitHub issue describing your use case.

$3

BackendTerminatedError is thrown when the backend is terminated by the user, i.e. pg_terminate_backend.

BackendTerminatedError must be handled at the connection level, i.e.

`js
await pool.connect(async (connection0) => {
try {
await pool.connect(async (connection1) => {
const backendProcessId = await connection1.oneFirst(sqlSELECT pg_backend_pid());

setTimeout(() => {
connection0.query(sqlSELECT pg_cancel_backend(${backendProcessId}))
}, 2000);

try {
await connection1.query(sqlSELECT pg_sleep(30));
} catch (error) {
// This code will not be executed.
}
});
} catch (error) {
if (error instanceof BackendTerminatedError) {
// Handle backend termination.
} else {
throw error;
}
}
});

`

$3

CheckIntegrityConstraintViolationError is thrown when PostgreSQL responds with check_violation (23514) error.

$3

ConnectionError is thrown when connection cannot be established to the PostgreSQL server.

$3

To handle the case where the data result does not match the expectations, catch DataIntegrityError error.

`js
import {
NotFoundError
} from 'slonik';

let row;

try {
row = await connection.one(sqlSELECT foo);
} catch (error) {
if (error instanceof DataIntegrityError) {
console.error('There is more than one row matching the select criteria.');
} else {
throw error;
}
}

`

$3

ForeignKeyIntegrityConstraintViolationError is thrown when PostgreSQL responds with foreign_key_violation (23503) error.

$3

To handle the case where query returns less than one row, catch NotFoundError error.

`js
import {
NotFoundError
} from 'slonik';

let row;

try {
row = await connection.one(sqlSELECT foo);
} catch (error) {
if (!(error instanceof NotFoundError)) {
throw error;
}
}

if (row) {
// row.foo is the result of the foo column value of the first row.
}

`

$3

NotNullIntegrityConstraintViolationError is thrown when PostgreSQL responds with not_null_violation (23502) error.

$3

StatementCancelledError is thrown when a query is cancelled by the user (i.e. pg_cancel_backend) or in case of a timeout.

It should be safe to use the same connection if StatementCancelledError is handled, e.g.

`js
await pool.connect(async (connection0) => {
await pool.connect(async (connection1) => {
const backendProcessId = await connection1.oneFirst(sqlSELECT pg_backend_pid());

setTimeout(() => {
connection0.query(sqlSELECT pg_cancel_backend(${backendProcessId}))
}, 2000);

try {
await connection1.query(sqlSELECT pg_sleep(30));
} catch (error) {
if (error instanceof StatementCancelledError) {
// Safe to continue using the same connection.
} else {
throw error;
}
}
});
});

`

$3

StatementTimeoutError inherits from StatementCancelledError and it is called only in case of a timeout.

$3

UniqueIntegrityConstraintViolationError is thrown when PostgreSQL responds with unique_violation (23505) error.

Types

This package is using TypeScript types.

Refer to ./src/types.js.

The public interface exports the following types:

* DatabaseConnectionType
* DatabasePoolConnectionType
* DatabaseSingleConnectionType

Use these types to annotate connection instance in your code base, e.g.

`js
import type {
DatabaseConnectionType
} from 'slonik';

export default async (
connection: DatabaseConnectionType,
code: string
): Promise => {
const countryId = await connection.oneFirst(sql
SELECT id
FROM country
WHERE code = ${code}
);

return countryId;
};

`

Debugging

$3

Slonik uses roarr to log queries.

To enable logging, define ROARR_LOG=true` environment variable.

By default, Slonik logs only connection events, e.g. when connection is created, connection is acquired and notices.

Query-level logging can be