Example 4: Statement matching — AllegroGraph Python client 105.1.0 documentation

# Example 4: Statement matching

The `getStatements()` method of the connection object provides a simple way to perform unsophisticated queries. This method lets you enter a mix of required values and wildcards, and retrieve all matching triples. (If you need to perform sophisticated tests and comparisons you should use a SPARQL query instead.)

Below, we illustrate two kinds of `getStatements()` calls. The first mimics traditional RDF4J syntax, and returns a `Statement` object at each iteration. We will reuse data from in previous examples to create a connection object and populate the repository with four triples describing Bob and Alice. We’re going to search for triples that mention Alice, so we have to create an “Alice” URI to use in the search pattern:

    from franz.openrdf.connect import ag_connect

    conn = ag_connect("python-tutorial", create=True, clear=True)

    conn.addData("""
        @base <http://example.org/> .

        <people/alice> a <ontology/Person> ;
                       <ontology/name> "Alice" .
        <people/bob> a <ontology/Person> ;
                     <ontology/name> "Bob" .
    """)
    alice = conn.createURI("http://example.org/people/alice")

Now we search for triples with Alice’s URI in the subject position. The `None` values are wildcards for the predicate and object positions of the triple.

    statements = conn.getStatements(alice, None, None)

The `getStatements()` method returns a `RepositoryResult` object (bound to the variable `statements` in this case). This object can be iterated over, exposing one result statement at a time. It is sometimes desirable to screen the results for duplicates, using the `enableDuplicateFilter()` method. Note, however, that duplicate filtering can be expensive. Our example does not contain any duplicates, but it is possible for them to occur.

    with statements:
        statements.enableDuplicateFilter()
        for statement in statements:
            print(statement)

This prints out the two matching triples for “Alice.”

    (<http://example.org/people/alice>, <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>, <http://example.org/ontology/Person>)
    (<http://example.org/people/alice>, <http://example.org/ontology/name>, "Alice")

Notice how we used the `with` keyword to ensure that the `RepositoryResult` object is closed after the results are fetched. This is necessary to release resources used during result retrieval. The same goal could be accomplished by calling the `RepositoryResult.close()` method (preferably in a `finally` block to ensure exception safety).