SafeFetching

This library offers a DSL (Domain Specific Language) to safely build predicates and requests to fetch a CoreData store.

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Convenient and Safe Fetching

The library requires to manually define the entity class. Then the macro FetchableManagedObject can be used.

@FetchableManagedObject
final class User: NSManagedObject {

    @NSManaged var score = 0.0
    @NSManaged var name: String? = ""
}

This makes User conform to Fetchable and ready to be used with the SafeFetching API.

Then it's possible to use the DSL to build a request. The last step can either get the built request as NSFetchRequest<User> or execute the request in the provided context.

User.request()
    .all(after: 10)
    .where { $0.score >= 15 || $0.name != "Joe" }
    .sorted(by: .ascending(\.score), .descending(\.name))
    .setting(\.returnsDistinctResults, to: true)
    .nsValue // returns NSFetchRequest<User>

User.request()
    .all(after: 10)
    .where { $0.score >= 15 || $0.name != "Joe" }
    .sorted(by: .ascending(\.score), .descending(\.name))
    .setting(\.returnsDistinctResults, to: true)
    .fetch(in: context) // returns [User]

Advanced NSPredicate operators are also available like BEGINSWITH (hasPrefix).

User.request()
    .all()
    .where { $0.name.hasPrefix("Do", options: .caseInsensitive) }
    .nsValue

More about predicates in the documentation.

Convenience for NS types

The library also offers convenience functions to set a predicate of a NSFetchRequest.

request.predicate = .safe(on: User.self) { $0.score.isIn(10...20 }
// or
request.predicate = .safe(on: User.self) { (10...20).contains($0.score) }

NSPredicate, Predicate

Why not using the Predicate macro? Two reasons.

• It works only with SwiftData as of today (so iOS 17+, macOS 14+ ...). It doesn't work with CoreData.
• It doesn't support everything that NSPredicate does when fetching a CoreData store.

Meanwhile, NSPredicate requires to write everything in a String, which is very error-prone.

Whereas this library tries to cover three objectives:

1. Use compiler-checking to evaluate predicates and avoid runtime errors.
2. Writing a request and especially a predicate should feel as natural as possible in Swift.
3. No feature of NSPredicate to fetch a CoreData store should be left behind.