Generic Query Parser

Convert a query string object to a generic db query.

Generates conditions, projection, and options (sort, skip, limit).

Works for generic usage or even better in combination with an ORM.
You can map REST APIs to mongodb driver, mongoose or sequelize queries.
Express and Koa middlewares are already provided.

Installation

``
npm install --save generic-query-parser
`

Usage

You can manually parse a query string or use one of the middlewares already provided to easily consume the parsed object in your server code.

$3

`javascript
// define your query
var query =
filter[age]=32
&operator[age]=gte
&type[age]=number
&filter[name]=^A.*
&type[name]=regexp
&limit=3
&skip=0
;

// require query string module (nested structures support)
var qs = require('qs');

// parse query to a nested object object
var requestQuery = qs.parse(query);

// require generic query parser
var Parser = require('generic-query-parser');

// parse request query to a db query
var dbQuery = Parser.parse(requestQuery)

// use parsed object
dbQuery.conditions;
dbQuery.projection;
dbQuery.options;
`

$3

#### Express

Simply use expressMiddleware provided with the module and req.custom in each subsequent middleware will be populated with conditions, projection and options.

`javascript
// create new express app
var express = require('express'),
app = express();

// require generic query parser
var Parser = require('generic-query-parser');

// use middleware
app.use(Parser.expressMiddleware);

// consume parsed results
app.use(function(req,res,next){
var dbQuery = req.custom;

dbQuery.conditions;
dbQuery.projection;
dbQuery.options;
})
`

#### Koa

Simply use koaMiddleware provided with the module and this.custom in each subsequent middleware will be populated with conditions, projection and options.

NOTE: Koa native query string module doesn't support nested structures. You need to use koa-qs module in order to use filter conditions.

`javascript
// create new koa app
var koa = require('koa'),
app = koa();

// use koa-qs module to parse query string to nested object
require('koa-qs')(app)

// require generic query parser
var Parser = require('generic-query-parser');

// use middleware
app.use(Parser.koaMiddleware);

// consume parsed results
app.use(function*(next){
var dbQuery = this.custom;

dbQuery.conditions;
dbQuery.projection;
dbQuery.options;
})
`

$3

#### Methods

parse(queryObject)

Parse a query string object to a db query

params

- Object queryObject: query string object

return

- Object: parsed query composed by: conditions, projection, options


expressMiddleware(req, res, next)

Use as a middleware for Express


koaMiddleware(next)

Use as a middleware for Koa


#### Syntax

##### Filters

Convert filter, operator and type from query to conditions object

Example:
`javascript
// age greather than or equal to 32 (converted to a number)
'filter[age]=32&operation[age]=gte&type[age]=number'
`

###### Filter values

Filter attributes by given value. Adds a condition for each attribute name received.

- Object filter: filter values
- String filter[attribute]: value to filter for given attribute

Example:
`javascript
// age 32
'filter[age]=32'

// color red
'filter[color]=red'

// name starts with 'A'
'filter[name]=^A.*'
`

###### Filter operators

Apply an operator to a filter value. Adds the given operator to the conditions.

- Object operator: filter operators
- String operator[attribute]: filter operator for the attribute, one of eq, gt, gte, lt, lte or ne

Example:
`javascript
// age greather or equal than
'operation[age]=gte'
`

###### Filter types

Apply an type to a filter value. Converts the value to the given type.

Some ORMs (or DBs) might do an implicit conversion and directly accept a string as parameter even if the db type is different. If this is not your case just use the type parameter.

- Object type: filter types
- String type[attribute]: filter type for attribute, one of string, number, date, bool, regexp or null

Example:
`javascript
// given age value is a number
'type[age]=number'

// given name value is a regex
'type[name]=regex'
`


##### Projection

- String fields: list of desired fields in the projection, comma or space separated


##### Sort

- String sort: list of sorting attributes, comma or space separated


##### Range

- Number limit: results amount, default 0
- Number skip: results offset, default 0

Example:
`javascript
// get the first 10
'skip=0&limit=10'

// get the next 10
'skip=10&limit=10'
``

LICENSE: MIT