CODEWITHSUNDEEP
swiftcore-datarelationshipnspredicate
Shane O'Seasnain
Shane O'Seasnain

Reputation: 3674

Nesting fetch requests

In my project, I have two entities: personEntity & municipalEntity. These have a many-to-many inverse relationship with each other. I execute a NSFetchRequest on personEntity to get a person's details:

    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let context = appDelegate.managedObjectContext
    let personRequest = NSFetchRequest(entityName: "personEntity")
    let personPred = NSPredicate(format: "surname = %@", "Smith")
    personRequest.predicate = personPred
    do {
        let personsList = try context.executeFetchRequest(personRequest)
        // this all clear enough up to this point

At this point, I try to nest a second, predicated FetchRequest within the first. This request should search municipalEntity in its peopleInMunicipality relationship property, for the objects from personsList. 

        for selectedPeople in personsList {
            let municipalRequest = NSFetchRequest(entityName: "municipalEntity")
            let municipalPred = NSPredicate(format: "peopleInMunicipality = %@", selectedPeople)
            municipalRequest.predicate = municipalPred
            do {
                let municipalitiesWithResidentsCalledSmithList = try context.executeFetchRequest(municipalRequest)

And bang... the compiler complains and suggests I need to change two things in the line defining the second predicate. It suggests instead...

            let municipalPred = NSPredicate(format: "peopleInMunicipality = %@", argumentArray: selectedPerson as? [AnyOject])

The compiler is now happy but when I run the code, it crashes with an EXC_BAD_ACCESS error on the suggested argumentArray: code section. Any idea how I can fix this?

Upvotes: 0

Views: 106

Answers (2)

Khundragpan
Khundragpan

Reputation: 1960

Since I cannot post comment. You can try SubQuery on MunicipalEntity like this:

     NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(peopleInMunicipality, $person, $person.surname == %@).@count > 0", @"Smith"];

Use this Predicate on Municipal Entity

Upvotes: 0

Willeke
Willeke

Reputation: 15598

vadian is right. You don't need the second fetch request. If the reverse relationship of peopleInMunicipality is called municipalities, the municipalities of selectedPeople is selectedPeople.municipalities.

If you really want to execute a second fetch request, the predicate format would be peopleInMunicipality CONTAINS %@.

Upvotes: 1

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