Create or Find a Relationship

    A relationship is treated as an object that can be used by more than one entity (see the discussion on IJC hierarchy). It is created in a similar way to entities, relying on identifying the correct class and then finding it in a list of appropriate new DFCapability types. Two options currently exist:DBRelationshipCapability and DBRelationshipMtoN.

    Most scripts that are creating a relationship will also be creating at least one of the entities within the same script. The example below assumes this. If you need to create a relationship between the root entity and another schema entity, you can generate a list of available entities via dataTree.schema.getEntities().getItems().

    def schema = dataTree.schema
    schema.lockable.withLock('Adding relationship'){ env ->
        // Create a structures entity and a standard entity
        def structuresEntity = DFEntities.createJChemEntity(schema, 'STRUCTURES', env)
        def dataEntity = DFEntities.createStandardEntity(schema, 'DATA', env)
        //Find the many:man relationship class and then create the relationship
        req = [ DBRelationshipMtoN.class]
        nt = DIFUtilities.findFirstAppropriateNewType(schema.getRelationships().getNewTypes(), false, req, new Class[0]);
        nt.options.newDFItemNameSafe = 'STRUCTURES to DATA'
        nt.options.srcField = structuresEntity.idField
        nt.options.dstField = dataEntity.idField
        nt.options.relType = DFRelationship.Type.MANY_TO_MANY
        assert nt.options.valid : 'Error: ' + nt.options.errorMessage

    The relationship can be called later in the script by replacing nt.create(env) with a defined variable, such as def rel = nt.create(env).iterator().next().

    Finding an existing relationship is an equally simple task. Simply query the entity for relationships, and then select from a list. When there is only one relationship, you can call the first one automatically:

     rel = DIFUtilities.findUsagesInRelationships(ety)
        firstRel = rel.get(0)

    This is demonstrated as part of a fully functional scriptlet in the Add Edge scriptlet. This approach isn't used as much, as it requires searching the schema for available tables, when most often they will be created as part of a script if a relationship is also created.