mysql-migrations

Table of contents

- Prerequisites
- Install
- Setup
- Adding Migrations
- Executing Migrations

Prerequisites

A node project with mysql used for database.

Install

It can be installed using npm.

``
npm install mysql-migrations
`

Setup


1. Create a directory where you wish to maintain all your migrations. We call it migrations.
2. Instantiate mysql-migrations by passing a mysql pool and the migrations directory path.

`


migration.js

var mysql = require('mysql');
var migration = require('mysql-migrations');

var connection = mysql.createPool({
connectionLimit : 10,
host : 'localhost',
user : 'root',
password : 'password',
database : 'your_database'
});

migration.init(connection, __dirname + '/migrations');
`

$3

If you want to execute something at the end of any migration, you can add third parameter as callback function. Example:

`


migration.js

var mysql = require('mysql');
var migration = require('mysql-migrations');

var connection = mysql.createPool({
connectionLimit : 10,
host : 'localhost',
user : 'root',
password : 'password',
database : 'your_database'
});

migration.init(connection, __dirname + '/migrations', function() {
console.log("finished running migrations");
});
`

Adding Migrations

$3

Run

`
node migration.js add migration create_table_users
`

Now open the migrations folder. Locate the newest file with greatest timestamp as it predecessor. The file will have the name which was specified in the command such as 12213545345_create_table_users.js

$3


Write the query in up key of the json created for the forward migration. As a part of good practice, also write the script to rollback the migration in down key. Ex.

`
module.exports = {
"up": "CREATE TABLE users (user_id INT NOT NULL, UNIQUE KEY user_id (user_id), name TEXT )",
"down": "DROP TABLE users"
}
`

$3


Run
`
node migration.js add seed create_table_users
`
to add a seed.

`
module.exports = {
"up": "UPDATE users SET name = 'John Snow' WHERE name = ''",
"down": "UPDATE users SET name = '' WHERE name = 'John Snow'"
}
`

$3

Run
`
node migration.js add migration create_table_users "CREATE TABLE mysql_migrations_347ertt3e (user_id INT NOT NULL, UNIQUE KEY user_id (user_id) )"
`
Locate the newest file with greatest timestamp as it predecessor and open it. Query will be automatically added as up key. However down key needs to be filled manually.

$3

You may initiate the migration file and add a function.

`
module.exports = {
'up' : function (conn, cb) {
conn.query ("UPDATE users set name = 'alen'", function (err, res) {
cb();
});
},
'down' : ""
}
`

Executing Migrations

There are few ways to run migrations.

1. Run node migration.js up. Runs all the pending up migrations.
2. Run node migration.js up 2. Runs 2 pending up migrations from the last position.
3. Run node migration.js down. Runs only 1 down migrations.
4. Run node migration.js refresh. Runs all down migrations followed by all up.

Example Output:

`
UP: "CREATE TABLE users2 (user_id INT NOT NULL, UNIQUE KEY user_id (user_id), name TEXT )"
UP: "CREATE TABLE users (user_id INT NOT NULL, UNIQUE KEY user_id (user_id), name TEXT )"
UP: "CREATE TABLE users1 (user_id INT NOT NULL, UNIQUE KEY user_id (user_id), name TEXT )"
No more "UP" migrations to run
`

$3

At times, few migrations need to run again or anonymously. There could be variety of reasons old migrations need to be executed or rollbacked. It can be done this way.

Up migration
`
node migration.js run 1500891087394_create_table_users.js up
`

Down migration
`
node migration.js run 1500891087394_create_table_users.js down
`

>> Since these are anonymous executions, no records are maintained for any executions.

Executing backdated migrations


Suppose there are few migrations which were merged late into the main branch. Technically, they should not run because they are old migrations and should already have been run, but it happens that someone has been working on a branch for long and once merged into master, the older migrations do not work because the latest migration timestamp is greater. There is a flag which can help in running those migrations. There are two ways:
1. Single Run
`
node migration.js up --migrate-all
`
2. For all runs, you can configure in the init part itself.
`

migration.js

var mysql = require('mysql');
var migration = require('mysql-migrations');

var connection = mysql.createPool({
connectionLimit : 10,
host : 'localhost',
user : 'root',
password : 'password',
database : 'your_database'
});

migration.init(connection, __dirname + '/migrations', function() {}, ["--migrate-all"]);
`
and then run migrations normally

`
node migration.js up
`

Saving Schema and Loading from Schema


Having schema.sql is good because it will help you review the schema changes in PR itself. The schema is stored in migrations folder under the file name schema.sql. There are two ways to generate schema.
1. Single Run
`
node migration.js up --update-schema
`
2. For all runs, you can configure in the init part itself.
`

migration.js

var mysql = require('mysql');
var migration = require('mysql-migrations');

var connection = mysql.createPool({
connectionLimit : 10,
host : 'localhost',
user : 'root',
password : 'password',
database : 'your_database'
});

migration.init(connection, __dirname + '/migrations', function() {}, ["--update-schema"]);
`
and then run migrations normally

`
node migration.js up
node migration.js down 2
..
`

Updated Schema will be stored in migrations folder after each run.

$3

Suppose you setup your project and you want to avoid running the entire migrations and simply want to load it from schema generated in the above process. You can do it via:

`
node migration.js load-from-schema
``

The above command will create all the tables and make entry in the logs table. It is helpful when setting up projects for newbies or environments without running entire migration process.

Pending

>>Test cases: Will pick up when I get time.

Help and Support

Will be more than happy to improve upon this version. This is an over night build and needs to be improved certainly. Will welcome everyone who wants to contribute.

Credits and other stuff

It is my first contribution to npm and I am sort of happy over it. I made this when I was really looking for a suitable tool with barebone settings allowing me to maintain database structure. I could not find a basic one and hence wrote my own and finally decided to publish. It took me around 2 hours to write the first version which barely works. But it still does my job.

>>Credits to my parents.