Class | ActiveRecord::ConnectionAdapters::TableDefinition |
In: |
lib/active_record/connection_adapters/abstract/schema_definitions.rb
|
Parent: | Object |
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 and change_table is actually of this type:
class SomeMigration < ActiveRecord::Migration def self.up create_table :foo do |t| puts t.class # => "ActiveRecord::ConnectionAdapters::TableDefinition" end end def self.down ... end end
The table definitions The Columns are stored as a ColumnDefinition in the columns attribute.
columns | [RW] | An array of ColumnDefinition objects, representing the column changes that have been defined. |
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):
For clarity‘s sake: the precision is the number of significant digits, while the scale is the number of digits that can be stored following the decimal point. For example, the number 123.45 has a precision of 5 and a scale of 2. A decimal with a precision of 5 and a scale of 2 can range from -999.99 to 999.99.
Please be aware of different RDBMS implementations behavior with :decimal columns:
This method returns self.
# 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) # Defines a column with a database-specific type. td.column(:foo, 'polygon') # => foo polygon
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