No exact matches in call to instance method 'setValue' for custom property

Question

I am trying to use a custom property inside a SwiftData model:

import SwiftData
struct Foo {
 var name: String
}
@Model
final class Bar {
 var id: String
 var name: String
 var foo: Foo
 
 init(id: String, name: String) {
 self.id = id
 self.name = name
 self.foo = Foo(name: name)
 }
}

This is just a simplified example, in my real project Foo has many more variables and functions.

I get the following three "No exact matches in call to instance method setValue or getValue" errors:

{
 @storageRestrictions(accesses: _$backingData, initializes: _foo)
 init(initialValue) {
 _$backingData.setValue(forKey: \.foo, to: initialValue)
 _foo = _SwiftDataNoType()
 }
 get {
 _$observationRegistrar.access(self, keyPath: \.foo)
 return self.getValue(forKey: \.foo)
 }
 set {
 _$observationRegistrar.withMutation(of: self, keyPath: \.foo) {
 self.setValue(forKey: \.foo, to: newValue)
 }
 }
}

How can I solve this?

EDIT

Here is my updated code using a computed property, and this compiles:

@Model
final class Bar {
 var id: String
 var name: String
 var foo: Foo {
 return Foo(name: name)
 }
 
 init(id: String, name: String) {
 self.id = id
 self.name = name
 }
}

However, if I try to change the name of foo:

func changeFoo(newName: String) {
 foo.name = newName
}

I get another error:

Cannot assign to property: 'foo' is a get-only property

• Sweeper: Why do you expect that SwiftData supports storing instances of some random Foo type? Please read the documentation. How about making Foo conform to Codable? It really depends on what properties Foo has and what their types are.
• koen: Ok, clear. Unfortunately, Foo is from an external package, and does not conform to Codable. And it has many other properties from the package. I tried making it a computed property, which compiles, but then I cannot make changes to it, even though it is a var.
• Sweeper: Well okay you need to declare a setter for the computed property too, e.g. set { self.name = newValue.name }. But why not just conform it to Codable? "From an external package" isn't really an excuse, unless you are anticipating that package will add its own Codable conformance and therefore conflict with yours?
• Sweeper: Actually, aren't you creating two sources of truth for "name" here if you used a stored property? What actually is the relationship between self.name and foo.name? If there is only one source of truth (self.name), then you can just use @Transient on the other property to have SwiftData ignore it.

Answer 1

EDIT:

Although the answer below works, in the end I was able to make Foo from the external package conform to Codable.

---

Thanks to @Sweeper for pointing me to @Transient.

The following code works for both my example, and real project:

import SwiftData
struct Foo {
 var name: String
}
@Model
final class Bar {
 var id: String
 var name: String
 
 @Transient
 var foo: Foo = .init(name: "")
 
 init(id: String, name: String) {
 self.id = id
 self.name = name
 }
 
 func changeFoo(newName: String) {
 foo.name = newName
 }
}

• Joakim Danielson: Or you could make foo a computed property with a get and set