Filtering core data using the reverse way

I have a core data entity with a property called eventTimes.

This eventTimes is a string property that may be empty or contain values like the four examples below.

```
9:00, 10:00, 14:00, 16:00
```
```
13:00
```

11:00, 12:00, 15:00, 18:00, 21:00, 23:00, 0:00

```
14:00, 16:00, 19:00
```

Now I need to filter that using NSPredicate based on a time value. It needs to be NSPredicate because it will be used with CoreData's NSFetchController and SwiftUI.

Example: give me the entries that contain 14:00.

I need to use something like

NSPredicate(format: "eventTimes IN %@", array )

But in my case is the opposite, that is eventTimes is the array and the object is the other element.

Something like

NSPredicate(format: "%@ IN eventTimes", oneTime )

But if I do that, it crashes.

Any way to do this?

Solution

eventTimes isn’t an array even if you want it to be. It’s a string and your predicate is crashing because of that fact.

You could use a compound predicate to compose a query against the string like:

NSPredicate(format: "eventTimes CONTAINS %@", timeString )

and form an array to be passed to

NSCompoundPredicate(orPredicateWithSubpredicates:)

But that gets rapidly messy so you’re better to do it right and form an EventTime entity with a many-to-one relationship to Event (Or whatever you’re calling the relevant entity).

This approach allows you to form complex time based searches e.g “Find me all events that start before 12:00” without using magic string formatting too.