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.

### Methods

[] belongs_to column new primary_key references timestamps to_sql

### Attributes

columns | [RW] | An array of ColumnDefinition objects, representing the column changes that have been defined.

### Public Class methods

new(base)

### Public Instance methods

[](name)

Returns a ColumnDefinition for the column with name `name`.

belongs_to(*args)

Alias for references

column(name, type, options = {})

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.

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:

- 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)

     # Defines a column with a database-specific type.
     td.column(:foo, 'polygon')
     # => foo polygon

## 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

primary_key(name)

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

references(*args)
timestamps(*args)

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

to_sql()

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.

[Validate]