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swiftcore-datansfetchrequest

Perform join in core data

In my app I have two entities, User and Meetings. What I want is a list of User who have meetings today.

Also, I haven't added relationship between both the entities. Is there any way through which I can query both the entities in a single fetch request. Or is there any other way.

Please help me to solve this in best possible way

Thanks in advance

Solution

  • Core Data tries to map objects from the OOP-world into tables and rows from the rDBMS-world and back. This is called a object-relational mapper (ORM). Even this looks very easy, because concepts seems to be similar, it is a difficult task. One called it the "Vietnam of information technology".

    However, at some point things do not go together. This is called the object-relational impedance mismatch (ORIM). At this point one has to decide, whether he takes the OOP-way or the rDBMS-way. Resolving relationships is one of this points.

    Core Data decided to do this the OOP-way: Relationships are treated as relationships between "usual" objects. This has two consequences:

    1. You do not join anything. In OOP objects are not joined. So in Core data objects are not joined. (However, they have some features in a fetch request with dictionaries, but this is not the usual way to access data in Core Data.)

    2. To do the job, Core Data needs to know the relationships between objects. You have to set the relationships.