Getter for 'subscript(dynamicMember:)' is unavailable

[StewartLynch]

I want to update a row with a swipe action as is done in the Reminders example and that works fine when toggling a bool, but I also want to update another property based on that updated boolean.
Is there a way to evaluate the QueryExpressopm value of the current boolean state and then update another property based on that value?
Can you point me in the right direction?

Button(item.isArchived ? "Unarchive" : "Archive"
    withErrorReporting {
        try database.write { db in
            try Item
                .find(item.id)
                .update {
                    // this give me an error Getter for 'subscript(dynamicMember:)' is unavailable
                    if $0.isArchived { 
                        $0.archiveDate = Date.now
                    } else {
                        $0.archiveDate = nil
                    }
                    // This works fine for toggling the boolean
                   $0.isArchived.toggle()
                }
                .execute(db)
        }
    }
}
.tint(item.isArchived ? .yellow : .green)

[StewartLynch]

I solved this by doing this, but I am wondering if there is a better way to do it.

Button(item.isArchived ? "Unarchive" : "Archive") {
    let updatedDate = item.isArchived ? nil : Date.now
    withErrorReporting {
        try database.write { db in
            try Item
                .find(item.id)
                .update {
                    $0.isArchived.toggle()
                    $0.archiveDate = updatedDate // Set archiveDate to nil when unarchiving or Date.now if archiving
                }
                .execute(db)
        }
    }
}
.tint(item.isArchived ? .yellow : .green)

[mbrandonw]

Hi @StewartLynch, the trailing closure of update does not have a builder context like other trailing closures do (e.g. where). So if statements are not supported, and even if they were you would not be able to do if $0.isArchived since $0.isArchived is a query expression of a boolean, not a boolean itself.

Ultimately you have to remember that all of this Swift syntax needs to be translated to SQL, and so it can be best to have an idea of how the final SQL should look like. In this case, you want to perform some ternary logic inside SQL, and the way that is done is using CASE/WHEN/THEN expressions, and our builder supports that syntax like so:

$0.archiveDate = Case().when($0.isArchived, then: Date())

[StewartLynch]

This is good for a single case, but I am having problems determining how to do the else clause with case(). CASE/WHEN/THEN/ELSE
I tried the following, but of course, this does not work

$0.archiveDate = Case().when($0.isArchived, then: Date(), else: nil)

Perhaps I should stop asking questions until I have completed the SQLite series

[mbrandonw]

Hi @StewartLynch, this isn't something we cover explicitly in our SQLiteData series, and is more related to SQL in general.

You do not need an else for your Case().when because you specifically want nil when the condition is not true, and that is the default behavior as detailed in the SQLite docs I linked to above:

If there is no ELSE expression and none of the WHEN expressions are true, then the overall result is NULL.

And so this compiles just fine for me:

@Table struct Foo {
  var isOn = false
  var date: Date?
}
func foo() {
  Foo.update {
    $0.date = Case().when($0.isOn, then: Date())
  }
}

Is it not compiling for you?

And if in the future you do need an else clause, it is not done in the when(_:then:) method because there can be multiple of those and there should only be a single else. So the else is defined as method you can put at the end of a chain:

Case().when($0.isOn, then: …).else(…)