How to model a @FetchOne query that should return a @Table object?

[thinkpractice]

Hi there,

I'm migrating my SwiftData code for my weight tracking app ScaleDiary to SharingGRDB. In the app, I'm retrieving the last weight entered by the user so the user can adjust the weight by clicking a plus or minus button. Often, weights only change in small amounts so this add some usability to the app. Of course, this weight should be optional as it may also be the first weight the user is entering. I was trying to retrieve the last weight entered by using the following code:

@ObservationIgnored
@FetchOnel(Weight.order { $0.timestamp.desc() }.limit(1))
var weightLastEntered: Weight? = nil

This however results in the following error Cannot convert value of type 'Select<(), Weight, ()>' to expected argument type '[Weight]' which leads me to believe optional values are not supported. Would this be something that should be possible in the future? Or are there any reasons this should or could not work?

For now, I've used a work-around but it would be nice if something similar as above would be present in future :)

kind regards,

Tim

[mbrandonw]

Hi @thinkpractice, we think this would be a good thing to have. Ideally @FetchOne could be used to service both situations, where a default is given and the type is non-optional, as well as the situation were no default is given and the type is optional. We just have to investigate things a bit more to see if that's possible, or how gnarly the overload space will be.

Failing that we could consider @FetchOne to always deal with optionals, and something like @FetchValue for dealing with non-optional/defaults.

[thinkpractice]

@mbrandonw a @FetchOne with a default parameter would be a great idea, but in some cases I guess you also would like an optional. In my case, for example, I'm checking whether the user already has entered a weight in the database. If so, the user can adjust the previous weight. If not, the user will have to enter a completely new value. In this case you would want an optional weight being nil right? Of course, it should be made possible by swift. If not possible I think your idea of adding the @FetchOne and @FetchValue distinction would be a logical alternative!

[stephencelis]

As an update to folks seeing this thread. It should now be possible to use @FetchOne with both optional and non-optional table rows if you are using version 0.5.0+ of the library.

[thinkpractice]

@stephencelis @mbrandonw thanks so much for this! I could now simplify my code to the following (as above):

@ObservationIgnored
@FetchOne(Weight.order { $0.timestamp.desc() }.limit(1))
var weightLastEntered: Weight?

Works like a charm!

[stephencelis]

Just a note, but @FetchOne should automatically apply limit(1), so you should be able to simplify.

[thinkpractice]

Of course! That’s what you get when copy+pasting some code in a hurry 😉 thanks! Op do 19 jun , Stephen Celis ***@***.***(mailto:Op do 19 jun , Stephen Celis <<a href=)> schreef:

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Just a note, but @FetchOne should automatically apply limit(1), so you should be able to simplify. — Reply to this email directly, [view it on GitHub](https://github.com/pointfreeco/sharing-grdb/discussions/61#discussioncomment-13522370), or [unsubscribe](https://github.com/notifications/unsubscribe-auth/AEOEDUQ7RTDJ6LBNDWT3G533ELTSPAVCNFSM6AAAAAB5WLXAXGVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGNJSGIZTOMA). You are receiving this because you were mentioned.Message ID: ***@***.***>