APPENDIX ?– ACTIVE RECORD METHODS IN DETAIL 241
Lastly, if you wish the create a UNIQUE index, use the :unique option:
add_index(:accounts, [:first_name, :last_name], :unique => true)
The SQL generated for this example would be CREATE UNIQUE INDEX accounts_first_
name_last_name_index ON accounts(first_name, last_name).
add_order_by_for_association_limiting!(sql, options)
With this method, you can modify the given SQL statement by adding the clause specified in
options[:order] to it. The PostgreSQL connection adapter overrides this method because of
its stricter standards compliance.
sql = "SELECT last_name FROM accounts"
add_order_by_for_association_limiting!(sql, :order => "last_name")
sql #=> "SELECT last_name FROM accounts ORDER BY last_name"
change_column(table_name, column_name, type, options = {})
The change_column method changes the specified column definition to match those specified
in options. See TableDefinition#column for details on what options you can use.
This method raises a NotEmplementedError by default and must be implemented by the
specific database connection adapters.
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