Rails migration for change column

I'm not aware if you can create a migration from the command line to do all this, but you can create a new migration, then edit the migration to perform this taks.

If tablename is the name of your table, fieldname is the name of your field and you want to change from a datetime to date, you can write a migration to do this.

You can create a new migration with:

rails g migration change_data_type_for_fieldname

Then edit the migration to use change_table:

class ChangeDataTypeForFieldname < ActiveRecord::Migration
  def self.up
    change_table :tablename do |t|
      t.change :fieldname, :date
    end
  end
  def self.down
    change_table :tablename do |t|
      t.change :fieldname, :datetime
    end
  end
end

Then run the migration:

rake db:migrate

Use #change_column.

change_column(:table_name, :column_name, :date)

# a few more examples:
change_column(:suppliers, :name, :string, limit: 80)
change_column(:accounts, :description, :text)

---

NOTE: the same result can be achieved even outside of db migrations, this might be handy for testing/debugging but this method needs to be used very cautiously:

ActiveRecord::Base.connection.change_column(:table_name, :column_name, :date)

As I found by the previous answers, three steps are needed to change the type of a column:

Step 1:

Generate a new migration file using this code:

rails g migration sample_name_change_column_type

Step 2:

Go to /db/migrate folder and edit the migration file you made. There are two different solutions.

1. def change
       change_column(:table_name, :column_name, :new_type)
   end
   

2.

    def up
        change_column :table_name, :column_name, :new_type
    end

    def down
        change_column :table_name, :column_name, :old_type
    end

Step 3:

Don't forget to do this command:

rake db:migrate

I have tested this solution for Rails 4 and it works well.

You can also use a block if you have multiple columns to change within a table.

Example:

change_table :table_name do |t|
  t.change :column_name, :column_type, {options}
end

See the API documentation on the Table class for more details.