I have loaded the custom query modules that I've created. How can I call it within the Memgraph?
Once the MAGE query modules or any custom modules you developed have been loaded into Memgraph, you can call them within queries using the following Cypher syntax:
CALL module.procedure(arg1, "string_argument", ...) YIELD res1, res2, ...;
Each procedure returns zero or more records, where each record contains named fields. The YIELD clause is used to select fields you are interested in or all of them (*). If you are not interested in any fields, omit the YIELD clause. The procedure will still run, but the record fields will not be stored in variables. If you are trying to YIELD fields that are not a part of the produced record, the query will result in an error.
Procedures can be standalone as in the example above, or a part of a larger query when we want the procedure to work on data the query is producing.
For example:
MATCH (node) CALL module.procedure(node) YIELD result RETURN *;
When the CALL clause is a part of a larger query, results from the query are returned using the RETURN clause. If the CALL clause is followed by a clause that only updates the data and doesn't read it, RETURN is unnecessary. It is the Cypher convention that read-only queries need to end with a RETURN, while queries that update something don't need to RETURN anything.
Also, if the procedure itself writes into the database, all the rest of the clauses in the query can only be read from the database, and the CALL clause can only be followed by the YIELD clause and/or RETURN clause.
If a procedure returns a record with the same field name as some variable we already have in the query, that field name can be aliased with some other name using the AS sub-clause:
MATCH (result) CALL module.procedure(42) YIELD result AS procedure_result RETURN *;