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Basic data. How to check if an object link exists without an error

There is object A and object B. Object B has one attribute, which is a transformable type (image), and one relation, which refers to object A. Object A may relate to one and only one, object B, or it may not be .

As I enumerate an array through my object, I want to check whether each object A has an object B. But I do not want to throw an error for object B (which will refer to the reverse imageToData NSValueTransformer). I just want to know if he is there or not. How can I do this without injecting object B into memory?

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2 answers

I think you can just check

if (objectA.relationshipToB != nil) ...

This will not cause an error for the associated object B , because you are not getting access to its properties.

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In Swift, I got

Could not find overload for '! = ', which accepts the provided arguments

error. My relationship was correctly marked as optional, but in the generated NSManagedObject my @NSManaged property was not ? after him. So this check with nil failed. Did I add ? and then I was able to check for a relationship.

Before (not working)

 @NSManaged var myRelationShip: MyClass

After (works)

 @NSManaged var myRelationShip: MyClass? // <--- Added `?`
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Source: https://habr.com/ru/post/958198/

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