module ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaStatements

def foreign_keys(table_name)
  scope = quoted_scope(table_name)
  fk_info = exec_query(<<~SQL, "SCHEMA")
    SELECT t2.oid::regclass::text AS to_table, a1.attname AS column, a2.attname AS primary_key, c.conname AS name, c.confupdtype AS on_update, c.confdeltype AS on_delete, c.convalidated AS valid, c.condeferrable AS deferrable, c.condeferred AS deferred
    FROM pg_constraint c
    JOIN pg_class t1 ON c.conrelid = t1.oid
    JOIN pg_class t2 ON c.confrelid = t2.oid
    JOIN pg_attribute a1 ON a1.attnum = c.conkey[1] AND a1.attrelid = t1.oid
    JOIN pg_attribute a2 ON a2.attnum = c.confkey[1] AND a2.attrelid = t2.oid
    JOIN pg_namespace t3 ON c.connamespace = t3.oid
    WHERE c.contype = 'f'
      AND t1.relname = #{scope[:name]}
      AND t3.nspname = #{scope[:schema]}
    ORDER BY c.conname
  SQL
  fk_info.map do |row|
    options = {
      column: Utils.unquote_identifier(row["column"]),
      name: row["name"],
      primary_key: row["primary_key"]
    }
    options[:on_delete] = extract_foreign_key_action(row["on_delete"])
    options[:on_update] = extract_foreign_key_action(row["on_update"])
    options[:deferrable] = extract_foreign_key_deferrable(row["deferrable"], row["deferred"])
    options[:validate] = row["valid"]
    to_table = Utils.unquote_identifier(row["to_table"])
    ForeignKeyDefinition.new(table_name, to_table, options)
  end
end