Migration Methods

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Create A Table:

	create_table :products do |t|
	  t.string :name, :null => false
	  t.integer :name
	end

The object yielded to the block in the create table method allows you to create columns. In this case, you can see we've generated to columns.

The above example is the "sexy" method of column creation, which uses the column type as the method on the column creator object. Below is the older school method that still gets the job done:

	create_table :products do |t|
	  t.column :name, :string, :null => false
	end

The only real difference here is swapping in the column method and adding column type as an argument. Both work. One uses less code. You can tell which one I prefer.

Change A Table

Much like the createtable method, only the object yielded to the block knows more tricks. For example, we can remove the description and name columns, create a partnumber column and add an index to it, and rename the column upccode to upc_code.

	change_table :products do |t|
	  t.remove :description, :name
	  t.string :part_number
	  t.index :part_number
	  t.rename :upccode, :upc_code
	end

Add/Remove Columns:

	def up
		add_column :table, :column, :type, :options
	end
	
	def down
		remove_column :table, :column
	end

Type options: :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, and :boolean.

Options include :null :default and :limit.

E.g.:

	add column :users, :username, :string, options: { null: false, limit: 30 } # A default value could be added, but it wouldn't make sense to have a default username.

Rename Column

	def up
		rename_column :table, :old_column_name, :new_column_name
	end
	
	def down
		rename_column :table, :new_column_name, :old_column_name
	end

Add/Remove Index:

Despite the id index that exists by default for each record, you may want to add indices to columns that are frequently searched in large tables to improve search speed.

	def up
		add_index :table_name, :column_name, :options
	end
	
	def down
		remove_index :table_name, :column => column_name # Removes index by specifying the column name
		
		:name => index_name # Removes index by specifying the index name
	end

Options include: :unique, and :order

	:options { unique: true, order: { :name => :desc } }

Rename Table:

	def up
		rename_table :old_name, :new_name
	end
	
	def down
		rename_table :new_name, :old_name
	end

Change Column Type & Options:

	def up
		change_column :table, :column, :new_type, :new_options
	end
	
	def down
		change_column :table, :column, :old_type, :old_options
	end