instance method exclusion_constraints

# File activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb, line 663
        def exclusion_constraints(table_name)
          scope = quoted_scope(table_name)

          exclusion_info = internal_exec_query(<<-SQL, "SCHEMA")
            SELECT conname, pg_get_constraintdef(c.oid) AS constraintdef, c.condeferrable, c.condeferred
            FROM pg_constraint c
            JOIN pg_class t ON c.conrelid = t.oid
            JOIN pg_namespace n ON n.oid = c.connamespace
            WHERE c.contype = 'x'
              AND t.relname = #{scope[:name]}
              AND n.nspname = #{scope[:schema]}
          SQL

          exclusion_info.map do |row|
            method_and_elements, predicate = row["constraintdef"].split(" WHERE ")
            method_and_elements_parts = method_and_elements.match(/EXCLUDE(?: USING (?<using>\S+))? \((?<expression>.+)\)/)
            predicate.remove!(/ DEFERRABLE(?: INITIALLY (?:IMMEDIATE|DEFERRED))?/) if predicate
            predicate = predicate.from(2).to(-3) if predicate # strip 2 opening and closing parentheses

            deferrable = extract_constraint_deferrable(row["condeferrable"], row["condeferred"])

            options = {
              name: row["conname"],
              using: method_and_elements_parts["using"].to_sym,
              where: predicate,
              deferrable: deferrable
            }

            ExclusionConstraintDefinition.new(table_name, method_and_elements_parts["expression"], options)
          end
        end