Core data max amount of entity

Question

I am working on an app where I use core data. I already have tried to do it with one entity but that didn't work. But I now have like twenty entities and my question is: is there a limit to the number of entities or a number recommended?
Is there a better way to store that amount of data?

UPDATE:

What I am storing are grads from school but not the A,b,c,d,e,f but a number from 1 to 10. And each grad has is own weighing(amount of times a number count) like some grad count 2 time because the are more imported.
So i first thought to have an array with a string for the name of the subject and then to array one store's the grad the other the corresponding weighing.
Like this:

var subjects: [String,[Int],[Int]] 

but this isn't possible and I don't even know how I should put this in core data and get it back properly.

Because I couldn't figure it out, I thought of just making a entity for each subject but there are a lot of them so there for this question.

Answer 1

You could setup a Subject entity that has one-to-many relationships to ordered sets of Grade and Weight, like so:

However, each grade apparently has a corresponding weight, so it would be more accurate to store each grade's weight in the Grade entity:

This still may not represent your real-world model.

• If your subject is something general, like math or english, you could have more than one subject per grade, (e.g., algebra, geometry, trigonometry), or more than one level per subject (e.g., algebra 1, algebra 2) which may or may not have a different grade.

• If your subject is very specific, your data may end up spread across unique one-to-one relationships, instead of one-to-many relationships.

You would also need to consider whether you can use ordered or unordered relationships, or whether an attribute exists that you can use to sort an entity.

You should consider these different facets of what you're trying to model (as well as the specific fetches you'd want to perform), before you try to design or implement the model, to allow you to efficiently represent this particular object graph.

Answer 2

There's no limit to the number of entities, but it's possible to go overboard and create more than you actually need. The recommended number is "as many as you need and no more", which obviously will vary a great deal depending on the nature of the data and how the app uses it. Whether there's a better way than your current approach is totally dependent on the fine details of exactly what you're doing, and so is impossible to answer without a far more detailed question.