Method: ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter#foreign_keys

Defined in:

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

#foreign_keys(table_name) ⇒ Object

Raises:

• (ArgumentError)

# File 'activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb', line 457

def foreign_keys(table_name)
  raise ArgumentError unless table_name.present?

  scope = quoted_scope(table_name)

  # MySQL returns 1 row for each column of composite foreign keys.
  fk_info = internal_exec_query(<<~SQL, "SCHEMA")
    SELECT fk.referenced_table_name AS 'to_table',
           fk.referenced_column_name AS 'primary_key',
           fk.column_name AS 'column',
           fk.constraint_name AS 'name',
           fk.ordinal_position AS 'position',
           rc.update_rule AS 'on_update',
           rc.delete_rule AS 'on_delete'
    FROM information_schema.referential_constraints rc
    JOIN information_schema.key_column_usage fk
    USING (constraint_schema, constraint_name)
    WHERE fk.referenced_column_name IS NOT NULL
      AND fk.table_schema = #{scope[:schema]}
      AND fk.table_name = #{scope[:name]}
      AND rc.constraint_schema = #{scope[:schema]}
      AND rc.table_name = #{scope[:name]}
  SQL

  grouped_fk = fk_info.group_by { |row| row["name"] }.values.each { |group| group.sort_by! { |row| row["position"] } }
  grouped_fk.map do |group|
    row = group.first
    options = {
      name: row["name"],
      on_update: extract_foreign_key_action(row["on_update"]),
      on_delete: extract_foreign_key_action(row["on_delete"])
    }

    if group.one?
      options[:column] = unquote_identifier(row["column"])
      options[:primary_key] = row["primary_key"]
    else
      options[:column] = group.map { |row| unquote_identifier(row["column"]) }
      options[:primary_key] = group.map { |row| row["primary_key"] }
    end

    ForeignKeyDefinition.new(table_name, unquote_identifier(row["to_table"]), options)
  end
end