Migration and seeding instructions using Knex.js!

Knex-Migrations-Seeding.md

Migrations & Seeding

What are migrations??

Migrations are a way to make database changes or updates, like creating or dropping tables, as well as updating a table with new columns with constraints via generated scripts. We can build these scripts via the command line using knex command line tool.

To learn more about migrations, check out this article on the different types of database migrations!

Creating/Dropping Tables

Let's create a Users and Tasks table using the knex command line tool. In the root of our project run the following commands:

$ knex migrate:make create_users_table
$ knex migrate:make create_tasks_table

The above commands will generate migration scripts in ./db/migrations with the given name plus a timestamp. (i.e. 20171024191043_create_user.js). This is on purpose so that knex can run the older migration files first, and then the newer ones that build on top of them.

The content of these files will stub out empty up and down functions to create or drop tables or columns.

We now want to build out the users and tasks table using some of the built in knex methods.

Example 20171024191043_create_user.js

exports.up = function(knex, Promise) {
  return knex.schema.createTable('users', function(table) {
    table.increments();
    table.string('email').notNullable();
    table.string('password').notNullable();
    table.timestamp('created_at').defaultTo(knex.fn.now())
    table.timestamp('updated_at').defaultTo(knex.fn.now())
  })
}

exports.down = function(knex, Promise) {
  return knex.schema.dropTable('users');
}

Example 20171024191043_create_task.js

exports.up = function(knex, Promise) {
  return knex.schema.createTable('tasks', function(table) {
    table.increments();
    table.string('title').notNullable();
    table.string('description').notNullable();
    table.boolean('is_complete').notNullable().defaultTo(false);
    table.integer('user_id').references('id').inTable('users');
    table.timestamp('created_at').defaultTo(knex.fn.now());
    table.timestamp('updated_at').defaultTo(knex.fn.now());
  })
}

exports.down = function(knex, Promise) {
  return knex.schema.dropTable('tasks');
}

Now we can run the below command performing a migration and updating our local database:

$ knex migrate:latest

Adding/Dropping Columns

Now, let's say that we want to add a column to either our Users or Tasks tables. Similar to creating a table, we can do this by creating another migration file that will be specifically for adding or removing a column from the desired table.

First lets create that migration script through knex.js

$ knex migrate:make add_fullname_to_users

Inside of our newly created migration script, we can now edit the exports.up and exports.down functions to look like this.

exports.up = function(knex, Promise) {
  knex.schema.table('users', function(table) {
    table.integer('fullname').notNull()
  })
}

exports.down = function(knex, Promise) {
  knex.schema.table('users', function(table) {
    table.dropColumn('fullname')
  })
}

Now we can run the knex:migrate command to update our existing table.

$ knex migrate:latest

And voila! We should now have a new column named fullname in our Users table.

Seeding Your Database

Similar to migrations, the knex module allows us to create scripts to insert initial data into our tables called seed files! If we have relations on our tables, the seeding must be in a specific order to so that we can rely on data that might already be in the database. For example, we must seed the users table first because our tasks table must validate a user id foreign key that already exists.

Lets create some seed files in this order:

$ knex seed:make 01_users
$ knex seed:make 02_tasks

Now lets insert some data into our seed scripts:

Example 01_users.js

exports.seed = function(knex, Promise) {
  // Deletes ALL existing entries
  return knex('users').del()
  .then(function () {
    // Inserts seed entries
    return knex('users').insert([
      {
        id: 1,
        email: '[email protected]',
        password: 'dorwssap'
      },
      {
        id: 2,
        email: '[email protected]',
        password: 'password1'
      },
      {
        id: 3
        email: '[email protected]',
        password: 'password123'
      }
    ]);
  });
};

Example 02_tasks.js

exports.seed = function(knex, Promise) {
  // Deletes ALL existing entries
  return knex('tasks').del()
  .then(function () {
    // Inserts seed entries
    return knex('tasks').insert([
      {
        title: 'Vaccuum the floors',
        description: 'Vaccum the living room and all bedroom',
        is_complete: false,
        user_id: 2
      },
      {
        title: 'Clean the car',
        description: 'Wash, wax and vacuum the car',
        is_complete: false,
        user_id: 1,
      },
      {
        title: 'Buy groceries',
        description: 'Milk, bread, cheese, eggs, flour',
        is_complete: true,
        user_id: 3,
      }
    ]);
  });
};

Now we can run the below command in the root of our project to seed our database!

$ knex seed:run