Dynamically filtering our SwiftData query

Paul Hudson @twostraws February 1st 2024

Our basic SwiftData query looks like this:

@Query(sort: \Prospect.name) var prospects: [Prospect]

By default that will load all Prospect model objects, sorting them by name, and while that's fine for the Everyone tab, it's not enough for the other two.

In our app, we have three instances of ProspectsView that vary only according to the FilterType property that gets passed in from our tab view. We’re already using that to set the title of each view, but we can also use it to filter our query.

Yes, we already have a default query in place, but if we add an initializer we can override that when a filter is set.

Add this initializer to ProspectsView now:

init(filter: FilterType) {
    self.filter = filter

    if filter != .none {
        let showContactedOnly = filter == .contacted

        _prospects = Query(filter: #Predicate {
            $0.isContacted == showContactedOnly
        }, sort: [SortDescriptor(\Prospect.name)])
    }
}

We've looked at creating queries manually previously, but there is one line that really stands out:

let showContactedOnly = filter == .contacted

If that made you do a double take, break it down into two parts. First, this check:

filter == .contacted

That will return true if filter is equal to .contacted, or false otherwise. And now this part:

let showContactedOnly =

That will assign the result of filter == .contacted to a new constant called showContactedOnly. So, if we read the whole line, it means "set showContactedOnly to true if our filter is set to .contacted." This makes our SwiftData predicate easy, because we can compare that constant directly against isContacted.

With that initializer in place, we can now create a List to loop over the resulting array. This will show both the title and email address for each prospect using a VStack – replace the existing text view in ProspectsView with this:

List(prospects) { prospect in
    VStack(alignment: .leading) {
        Text(prospect.name)
            .font(.headline)
        Text(prospect.emailAddress)
            .foregroundStyle(.secondary)
    }
}

If you run the app again you’ll see things are starting to look much better.