Rails migration shortcuts you might not know of!

These are definitely listed in the Rails guide, but I rarely see anyone use these so I wasn’t aware they existed!

Specifying modifiers

Type Modifiers are listed here. Things like, setting default values, null constraints, and character limits. Apparently, you can specify some of them in the generator command.

Of course, they don’t just TELL you which ones you can use 😩 that would be too easy. After searching for a long while I found the source code and I think these are the only currently supported modifiers:

• limit: Sets the maximum number of characters for a string column and the maximum number of bytes for string/text/binary/integer columns.
• precision: Specifies the precision for decimal/numeric/datetime/time columns.
• scale: Specifies the scale for the decimal and numeric columns, representing the number of digits after the decimal point.
• polymorphic: When generating with references, this option will create two columns which can be used for polymorphic associations: <column_name>_type and <column_name>_id.

To specify these modifiers, you need to pass values enclosed in curly braces after the field type like this:

Limit:

rails g migration AddNameToUsers name:string{40}

Precision and Scale:

rails g migrationAddAmountToProducts amount:decimal{10.2}

You must set both precision and scale at once.

Polymorphic

rails g migration add_supplier_to_products supplier:references{polymorphic}

Specifying indexes

A third value can be specified using another : after the column name and type, to configure the index of the column. This could also be the second option if the column type is a String.

:index: will just add an index

  add_column :products, :amount, :string
  add_index :products, :amount

:uniq: will add unique: true in the migration.

Creating join tables

Migration names containing JoinTable will generate join tables for use with has_and_belongs_to_many associations.

rails g migration CreateJoinTableCustomerProduct customer product

will create the migration:

def change
  create_join_table :customers, :products do |t|
    # t.index [:customer_id, :product_id]
    # t.index [:product_id, :customer_id]
  end
end

Nice.