Custom modules

Your application will likely have a custom module. It contains the relations your application adds. Each relation is linked to a database table, executes a command, or performs any other custom behaviour.

Here’s an example that shows you the basics. The module can take a data source as a dependency if it needs to retrieve and store records. The constructor defines its relations. The rest of the class contains the implementations of each of the relations.

class SIRModule(SomeModule):

    ds: SomeDataSource


    def __init__(self, data_source: SomeDataSource) -> None:
        super().__init__()
        self.ds = data_source
        self.add_relation(Relation("have", query_function=self.have))
        self.add_relation(Relation("part_of_n", query_function=self.part_of_n, write_function=self.common_write, arguments=['part', 'whole', 'number'])),


    def part_of_n(self, values: list, context: ExecutionContext) -> list[list]:
        part_variable = context.arguments[0]
        whole_variable = context.arguments[1]

        results = self.ds.select(context.relation.predicate, context.relation.arguments, values)

        return results


    # have(whole, part)
    # the verb have is always very abstract, but in this case it also handles with information on the class-level
    def have(self, values: list, context: ExecutionContext) -> list[list]:

        # solving based on class information

        whole_variable = context.arguments[0]
        part_variable = context.arguments[1]

        whole_type = None
        if isinstance(whole_variable, Variable):
            whole_type = self.get_name(context, whole_variable.name, values[0])

        part_type = None
        if isinstance(part_variable, Variable):
            part_type = self.get_name(context, part_variable.name, values[1])

        results = context.solver.solve([('part_of_number', part_type, whole_type, Variable('N'))])

        if len(results) == 0:
            raise ProcessingException(f"Don't know whether {part_type} is part of {whole_type}")

        number = results[0]['N']
        response = ResultIterator([None, None], number)

        return response

ResultIterator

The example class above demonstrates the ResultIterator. This object is useful in the edge case where you need to return a set of instances, but these instances don’t have an individual identity. It is used in combination with count, where a possibly very large set of instances is expected, but we’re only interested in the number of them. The ResultIterator object ensures that the length of the object is returned directly, without iterating over all items. The the SIR demo for an example.