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class ActiveRecord::ConnectionAdapters::TableDefinition

Active Record Connection Adapters Table Definition

Represents the schema of an SQL table in an abstract way. This class provides methods for manipulating the schema representation.

Inside migration files, the t object in create_table is actually of this type:

class SomeMigration < ActiveRecord::Migration[8.1]
  def up
    create_table :foo do |t|
      puts t.class  # => "ActiveRecord::ConnectionAdapters::TableDefinition"
    end
  end

  def down
    ...
  end
end

Inherits From

Attributes

[R] as
[R] check_constraints
[R] comment
[R] foreign_keys
[R] if_not_exists
[R] indexes
[R] name
[R] options
[R] temporary

Public class methods

Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 367
def initialize(
  conn,
  name,
  temporary: false,
  if_not_exists: false,
  options: nil,
  as: nil,
  comment: nil,
  **
)
  @conn = conn
  @columns_hash = {}
  @indexes = []
  @foreign_keys = []
  @primary_keys = nil
  @check_constraints = []
  @temporary = temporary
  @if_not_exists = if_not_exists
  @options = options
  @as = as
  @name = name
  @comment = comment
end

Public instance methods

Returns a ColumnDefinition for the column with name name.

Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 417
def [](name)
  @columns_hash[name.to_s]
end

Alias for: references.

Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 521
def check_constraint(expression, **options)
  check_constraints << new_check_constraint_definition(expression, options)
end

Instantiates a new column for the table. See connection.add_column for available options.

Additional options are:

  • :index - Create an index for the column. Can be either true or an options hash.

This method returns self.

Examples

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

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 do |t|
  t.column :shop_id,     :integer
  t.column :creator_id,  :integer
  t.column :item_number, :string
  t.column :name,        :string, default: "Untitled"
  t.column :value,       :string, default: "Untitled"
  t.column :created_at,  :datetime
  t.column :updated_at,  :datetime
end
add_index :products, :item_number

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

create_table :products do |t|
  t.integer :shop_id, :creator_id
  t.string  :item_number, index: true
  t.string  :name, :value, default: "Untitled"
  t.timestamps null: false
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. The :index option will also create an index, similar to calling add_index. 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
add_index :taggings, :tag_id, name: 'index_taggings_on_tag_id'
add_index :taggings, [:tagger_id, :tagger_type]

Can also be written as follows using references:

create_table :taggings do |t|
  t.references :tag, index: { name: 'index_taggings_on_tag_id' }
  t.references :tagger, polymorphic: true
  t.references :taggable, polymorphic: { default: 'Photo' }, index: false
end
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 488
def column(name, type, index: nil, **options)
  name = name.to_s
  type = type.to_sym if type

  raise_on_duplicate_column(name)
  @columns_hash[name] = new_column_definition(name, type, **options)

  if index
    index_options = index.is_a?(Hash) ? index : {}
    index(name, **index_options)
  end

  self
end

Returns an array of ColumnDefinition objects for the columns of the table.

Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 414
def columns; @columns_hash.values; end
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 517
def foreign_key(to_table, **options)
  foreign_keys << new_foreign_key_definition(to_table, options)
end

Adds index options to the indexes hash, keyed by column name This is primarily used to track indexes that need to be created after the table

index(:account_id, name: 'index_projects_on_account_id')
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 513
def index(column_name, **options)
  indexes << [column_name, options]
end

Also aliased as: belongs_to.

Adds a reference.

t.references(:user)
t.belongs_to(:supplier, foreign_key: true)
t.belongs_to(:supplier, foreign_key: true, type: :integer)

See connection.add_reference for details of the options you can use.

Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 547
def references(*args, **options)
  args.each do |ref_name|
    ReferenceDefinition.new(ref_name, **options).add_to(self)
  end
end

remove the column name from the table.

remove_column(:account_id)
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 505
def remove_column(name)
  @columns_hash.delete name.to_s
end
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 391
def set_primary_key(table_name, id, primary_key, **options)
  if id && !as
    pk = primary_key || Base.get_primary_key(table_name.to_s.singularize)

    if id.is_a?(Hash)
      options.merge!(id.except(:type))
      id = id.fetch(:type, :primary_key)
    end

    if pk.is_a?(Array)
      primary_keys(pk)
    else
      primary_key(pk, id, **options)
    end
  end
end

Appends :datetime columns :created_at and :updated_at to the table. See connection.add_timestamps

t.timestamps null: false
Source code GitHub
# File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 529
def timestamps(**options)
  options[:null] = false if options[:null].nil?

  if !options.key?(:precision) && @conn.supports_datetime_with_precision?
    options[:precision] = 6
  end

  column(:created_at, :datetime, **options)
  column(:updated_at, :datetime, **options)
end

Definition files