Returning created records from synchronous transactions #51

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adam · 2025-12-29T15:23:06+01:00

adam commented

2025-12-29 15:23:06 +01:00

Originally created by @jamesbebbington on GitHub (Apr 22, 2016).

Hey John,

I may be being a bit stupid here but, from having read the README it's not clear to me how I should be returning NSManagedObjects from synchronous transactions. I see CoreStore provides fetchExisting but I'm not sure how to use it in this example:

func createFoo() -> Foo? {
    guard let result = CoreStore.beginSynchronous({ transaction in
        let foo = transaction.create(Into(Foo))
        foo.createdAt = NSDate()
        transaction.commitAndWait()
    }) else { return nil }

    switch result {
    case .Success:
        return ? // How do I return the newly created Foo instance
    case .Failure:
        return nil
    }
}

Thanks.

Originally created by @jamesbebbington on GitHub (Apr 22, 2016). Hey John, I may be being a bit stupid here but, from having read the README it's not clear to me how I should be returning `NSManagedObject`s from synchronous transactions. I see CoreStore provides `fetchExisting` but I'm not sure how to use it in this example: ``` swift func createFoo() -> Foo? { guard let result = CoreStore.beginSynchronous({ transaction in let foo = transaction.create(Into(Foo)) foo.createdAt = NSDate() transaction.commitAndWait() }) else { return nil } switch result { case .Success: return ? // How do I return the newly created Foo instance case .Failure: return nil } } ``` Thanks.

adam added the question label 2025-12-29 15:23:06 +01:00

adam closed this issue

2025-12-29 15:23:07 +01:00

adam commented

2025-12-29 15:23:07 +01:00

@JohnEstropia commented on GitHub (Apr 23, 2016):

You'll need to assign it to an outer variable.

var foo: Foo? // Foo!
guard let result = CoreStore.beginSynchronous({ transaction in
    foo = transaction.create(Into(Foo))
    foo?.createdAt = NSDate()
    transaction.commitAndWait()
}) else { return nil }

switch result {
    case .Success:
        return foo.flatMap(CoreStore.fetchExisting) // CoreStore.fetchExisting(foo!)
    case .Failure:
        return nil
}

The risk of deadlock with synchronous transactions are kind of worrying though. I recommend you use asynchronous transactions instead, or to call beginSynchronous() from a background thread.

Otherwise, if you are just creating a new object and you don't need to fetch from within the transaction, it might actually be safe and performant to not rely on the transaction queueing mechanism.

let transaction = CoreStore.beginUnsafe()
let foo = transaction.create(Into(Foo))
foo.createdAt = NSDate()
transaction.commitAndWait()

return CoreStore.fetchExisting(foo)

@JohnEstropia commented on GitHub (Apr 23, 2016): You'll need to assign it to an outer variable. ``` swift var foo: Foo? // Foo! guard let result = CoreStore.beginSynchronous({ transaction in foo = transaction.create(Into(Foo)) foo?.createdAt = NSDate() transaction.commitAndWait() }) else { return nil } switch result { case .Success: return foo.flatMap(CoreStore.fetchExisting) // CoreStore.fetchExisting(foo!) case .Failure: return nil } ``` The risk of deadlock with synchronous transactions are kind of worrying though. I recommend you use asynchronous transactions instead, or to call `beginSynchronous()` from a background thread. Otherwise, if you are just creating a new object and you don't need to fetch from within the transaction, it might actually be safe and performant to not rely on the transaction queueing mechanism. ``` swift let transaction = CoreStore.beginUnsafe() let foo = transaction.create(Into(Foo)) foo.createdAt = NSDate() transaction.commitAndWait() return CoreStore.fetchExisting(foo) ```

adam commented

2025-12-29 15:23:08 +01:00

@jamesbebbington commented on GitHub (Apr 25, 2016):

Thanks John, that's what I was looking for. And thanks for the warning about deadlocks, I'll try and migrate over to asynchronous transactions.

@jamesbebbington commented on GitHub (Apr 25, 2016): Thanks John, that's what I was looking for. And thanks for the warning about deadlocks, I'll try and migrate over to asynchronous transactions.

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Reference: starred/CoreStore#51