[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 280
280:       def initialize(base)
281:         @columns = []
282:         @base = base
283:       end

Returns a ColumnDefinition for the column with name name.

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 292
292:       def [](name)
293:         @columns.find {|column| column.name.to_s == name.to_s}
294:       end

Alias for references

Instantiates a new column for the table. The type parameter is normally one of the migrations native types, which is one of the following: :primary_key, :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, :boolean.

You may use a type not in this list as long as it is supported by your database (for example, "polygon" in MySQL), but this will not be database agnostic and should usually be avoided.

Available options are (none of these exists by default):

• :limit - Requests a maximum column length. This is number of characters for :string and :text columns and number of bytes for :binary and :integer columns.
• :default - The column‘s default value. Use nil for NULL.
• :null - Allows or disallows NULL values in the column. This option could have been named :null_allowed.
• :precision - Specifies the precision for a :decimal column.
• :scale - Specifies the scale for a :decimal column.

Please be aware of different RDBMS implementations behavior with :decimal columns:

• The SQL standard says the default scale should be 0, :scale <= :precision, and makes no comments about the requirements of :precision.
• MySQL: :precision [1..63], :scale [0..30]. Default is (10,0).
• PostgreSQL: :precision [1..infinity], :scale [0..infinity]. No default.
• SQLite2: Any :precision and :scale may be used. Internal storage as strings. No default.
• SQLite3: No restrictions on :precision and :scale, but the maximum supported :precision is 16. No default.
• Oracle: :precision [1..38], :scale [-84..127]. Default is (38,0).
• DB2: :precision [1..63], :scale [0..62]. Default unknown.
• Firebird: :precision [1..18], :scale [0..18]. Default (9,0). Internal types NUMERIC and DECIMAL have different storage rules, decimal being better.
• FrontBase?: :precision [1..38], :scale [0..38]. Default (38,0). WARNING Max :precision/:scale for NUMERIC is 19, and DECIMAL is 38.
• SqlServer?: :precision [1..38], :scale [0..38]. Default (38,0).
• Sybase: :precision [1..38], :scale [0..38]. Default (38,0).
• OpenBase?: Documentation unclear. Claims storage in double.

This method returns self.

Examples

 # Assuming td is an instance of TableDefinition
 td.column(:granted, :boolean)
 # granted BOOLEAN

 td.column(:picture, :binary, :limit => 2.megabytes)
 # => picture BLOB(2097152)

 td.column(:sales_stage, :string, :limit => 20, :default => 'new', :null => false)
 # => sales_stage VARCHAR(20) DEFAULT 'new' NOT NULL

 td.column(:bill_gates_money, :decimal, :precision => 15, :scale => 2)
 # => bill_gates_money DECIMAL(15,2)

 td.column(:sensor_reading, :decimal, :precision => 30, :scale => 20)
 # => sensor_reading DECIMAL(30,20)

 # While <tt>:scale</tt> defaults to zero on most databases, it
 # probably wouldn't hurt to include it.
 td.column(:huge_integer, :decimal, :precision => 30)
 # => huge_integer DECIMAL(30)

Short-hand examples

Instead of calling column directly, you can also work with the short-hand definitions for the default types. They use the type as the method name instead of as a parameter and allow for multiple columns to be defined in a single statement.

What can be written like this with the regular calls to column:

  create_table "products", :force => true do |t|
    t.column "shop_id",    :integer
    t.column "creator_id", :integer
    t.column "name",       :string,   :default => "Untitled"
    t.column "value",      :string,   :default => "Untitled"
    t.column "created_at", :datetime
    t.column "updated_at", :datetime
  end

Can also be written as follows using the short-hand:

  create_table :products do |t|
    t.integer :shop_id, :creator_id
    t.string  :name, :value, :default => "Untitled"
    t.timestamps
  end

There‘s a short-hand method for each of the type values declared at the top. And then there‘s TableDefinition#timestamps that‘ll add created_at and updated_at as datetimes.

TableDefinition#references will add an appropriately-named _id column, plus a corresponding _type column if the :polymorphic option is supplied. If :polymorphic is a hash of options, these will be used when creating the _type column. So what can be written like this:

  create_table :taggings do |t|
    t.integer :tag_id, :tagger_id, :taggable_id
    t.string  :tagger_type
    t.string  :taggable_type, :default => 'Photo'
  end

Can also be written as follows using references:

  create_table :taggings do |t|
    t.references :tag
    t.references :tagger, :polymorphic => true
    t.references :taggable, :polymorphic => { :default => 'Photo' }
  end

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 419
419:       def column(name, type, options = {})
420:         column = self[name] || ColumnDefinition.new(@base, name, type)
421:         if options[:limit]
422:           column.limit = options[:limit]
423:         elsif native[type.to_sym].is_a?(Hash)
424:           column.limit = native[type.to_sym][:limit]
425:         end
426:         column.precision = options[:precision]
427:         column.scale = options[:scale]
428:         column.default = options[:default]
429:         column.null = options[:null]
430:         @columns << column unless @columns.include? column
431:         self
432:       end

Appends a primary key definition to the table definition. Can be called multiple times, but this is probably not a good idea.

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 287
287:       def primary_key(name)
288:         column(name, :primary_key)
289:       end

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 454
454:       def references(*args)
455:         options = args.extract_options!
456:         polymorphic = options.delete(:polymorphic)
457:         args.each do |col|
458:           column("#{col}_id", :integer, options)
459:           column("#{col}_type", :string, polymorphic.is_a?(Hash) ? polymorphic : options) unless polymorphic.nil?
460:         end
461:       end

Appends :datetime columns :created_at and :updated_at to the table.

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 448
448:       def timestamps(*args)
449:         options = args.extract_options!
450:         column(:created_at, :datetime, options)
451:         column(:updated_at, :datetime, options)
452:       end

Returns a String whose contents are the column definitions concatenated together. This string can then be prepended and appended to to generate the final SQL to create the table.

[Source]

     # File vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 467
467:       def to_sql
468:         @columns * ', '
469:       end