# Writing Our Own Migrations

## Objectives

* Write your own migrations
* Run a migration to create a table
* Run a migration to add a column to a table
* Run a migration to change something in the table

## Creating a Table

The first thing we will do is create a table. In `db/migrate/01_create_students.rb`, write the code to create a table with Active Record. We've created a class for you called `CreateStudents`.

Define a method called `change` and use the Active Record `create_table` method within that method to create the table. The table should have a `:name` column with a type `string`.

After you finish defining the `change` method, run the migrations by running `rake db:migrate` in your terminal.

## Adding a Column

The next thing we will do is add a couple of columns to the `students` table we just created. To do this, we will create a second migration file. *We cannot add these columns to the existing file.* Let's call our new file `02_add_grade_and_birthdate_to_students.rb`. It should live in `db/migrate` just like the first migration.

This new migration will look similar to the previous one. We will need a class that inherits from `ActiveRecord::Migration`, and we will need to define a change method. Sticking to conventions, name the class `AddGradeAndBirthdateToStudents`, since that is what we're doing (and that is the camel case version of the *filename*, minus the numbers in front). Inside `#change`, instead of `create_table`, we will use the `add_column` Active Record method.

Let's add a `:grade` column and a `:birthdate` column. The `:grade` column type should be `integer` and the `:birthdate` column type should be `string`.

## Changing a Column

Imagine you're creating an incredible web app to send out a birthday greeting on each student's birthday. While building this, you realize you accidentally stored your birthdate data as a `string`. It would be much easier to work with if the column type was `datetime` instead. Let's fix that.

Finally, we will change a column type, `string` to `datetime`. Same as before, you'll have to *create another migration file*. This time call it `03_change_datatype_for_birthdate.rb`. Once again, name the class the same name as the file but with capital letters instead of underscores: `ChangeDatatypeForBirthdate`.

This migration will have the same setup as the last. Be sure to use the `change_column` method. It takes three necessary arguments: `change_column(table_name, column_name, type)`.

## Active Record 5.x Migration Syntax

***NOTE***: As of Active Record 5.x, we can no longer inherit directly from `ActiveRecord::Migration` and must instead specify which version of Active Record / Rails the migration was written for. If we were writing a migration for Active Record 5.1, we would inherit from `ActiveRecord::Migration[5.1]`. Don't worry too much about this until you get to the Rails section. Until then, if you encounter an error like this...

```
StandardError: Directly inheriting from ActiveRecord::Migration is not supported. Please specify the Rails release the migration was written for:

  class CreateDogs < ActiveRecord::Migration[5.2]
```

...simply add `[5.2]` to the end of `ActiveRecord::Migration`, exactly as the error message instructs.

View [Writing Our Own Migrations](https://github.com/learn-co-curriculum/writing-migrations) on Learn.co and start learning to code for free.