2020-02-04

Data Nucleus Contains Function

I have been recently working with Data Nucleus and have found the contains() function to have an interesting use. Consider this code that executes a Data Nucleus query;

Query<Consignment> query = pm.newQuery(Consignment.class);
query.setFilter("this.parts.contains(p) && p.code == inPartCode");
query.declareParameters("String inPartCode");
query.declareVariables("Part p");
query.setNamedParameters(Map.of("inPartCode", partCode);
query.executeResultList(Consignment.class);

In this case only a Consignment that has a Part with the supplied code will be returned. This is how the SQL query might look for this;

SELECT DISTINCT "A0"."CODE", "A0"."ID"
FROM "CONSIGNMENT" "A0"
         INNER JOIN "PART" "B0" ON "A0"."ID" = "B0"."CONSIGNMENT_ID_OID"
WHERE "B0"."CODE" = 'P391233'