Let's Write Some Migrations

##Objectives

1. Write your own migrations
2. Run a migration to create a table
3. Run a migration to add a column to a table
4. 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 ActiveRecord. We've created a class for you called CreateStudents. To get access to the ActiveRecord methods, don't forget to inherit from ActiveRecord::Migration.

Next, define a method called change and use the ActiveRecord 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. Inside #change, instead of create_table, we will use the add_column ActiveRecord 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.

Again, same setup as before. Be sure to use the change_column method. It takes three necessary arguments: change_column(table_name, column_name, type).

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