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[amplify-libraries][Flutter] Document copyWithModelFieldValues for null fields #8619

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[amplify-libraries][Flutter] Document copyWithModelFieldValues for null fields #8619

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72cdeb7
Document copyWithModelFieldValues for nullable fields
AzazelSensei Aug 27, 2026
38c84cb
Document copyWithModelFieldValues on gen 2 mutate pages
AzazelSensei Aug 30, 2026
3d91e6c
Document copyWithModelFieldValues when clearing belongs-to links
AzazelSensei Sep 1, 2026
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12 changes: 12 additions & 0 deletions src/fragments/lib/datastore/flutter/data-access/update-snippet.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -19,3 +19,15 @@ Future<void> updatePost() async {
}
}
```

<Callout>

`copyWith` cannot assign `null` to a nullable field: a null argument keeps the current value. Use `copyWithModelFieldValues` instead:

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</Callout>

```dart
final newPost = oldPost.copyWithModelFieldValues(
content: ModelFieldValue.value(null),
);
```
18 changes: 18 additions & 0 deletions src/fragments/lib/graphqlapi/flutter/mutate-data.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,24 @@ Future<void> updateTodo(Todo originalTodo) async {
}
```

<Callout>

`copyWith` cannot assign `null` to a nullable field: a null argument keeps the current value. Use `copyWithModelFieldValues` instead:

</Callout>

```dart
Future<void> clearTodoDescription(Todo originalTodo) async {
final cleared = originalTodo.copyWithModelFieldValues(
description: ModelFieldValue.value(null),
);

final request = ModelMutations.update(cleared);
final response = await Amplify.API.mutate(request: request).response;
safePrint('Response: $response');
}
```

To delete the `Todo`:

```dart
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8 changes: 6 additions & 2 deletions src/pages/[platform]/build-a-backend/data/data-modeling/relationships/index.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -263,7 +263,9 @@ do {
<InlineFilter filters={["flutter"]}>

```dart
final memberWithRemovedTeam = existingMember.copyWith(team: null);
final memberWithRemovedTeam = existingMember.copyWithModelFieldValues(
teamId: ModelFieldValue.value(null),
);
final memberRemoveRequest = ModelMutations.update(memberWithRemovedTeam);
final memberRemoveResponse = await Amplify.API.mutate(request: memberRemoveRequest).response;
```
Expand Down Expand Up @@ -687,7 +689,9 @@ do {
<InlineFilter filters={["flutter"]}>

```dart
final cartWithRemovedCustomer = existingCart.copyWith(customer: null);
final cartWithRemovedCustomer = existingCart.copyWithModelFieldValues(
customerId: ModelFieldValue.value(null),
);
final cartRemoveRequest = ModelMutations.update(cartWithRemovedCustomer);
final cartRemoveResponse = await Amplify.API.mutate(request: cartRemoveRequest).response;
```
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18 changes: 18 additions & 0 deletions src/pages/[platform]/build-a-backend/data/mutate-data/index.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -293,6 +293,24 @@ Future<void> updateTodo(Todo originalTodo) async {
}
```

<Callout>

`copyWith` cannot assign `null` to a nullable field: a null argument keeps the current value. Use `copyWithModelFieldValues` instead:

</Callout>

```dart
Future<void> clearTodoDescription(Todo originalTodo) async {
final cleared = originalTodo.copyWithModelFieldValues(
description: ModelFieldValue.value(null),
);

final request = ModelMutations.update(cleared);
final response = await Amplify.API.mutate(request: request).response;
safePrint('Response: $response');
}
```

</InlineFilter>

## Delete an item
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18 changes: 18 additions & 0 deletions src/pages/[platform]/frontend/data/mutate-data/index.mdx
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -293,6 +293,24 @@ Future<void> updateTodo(Todo originalTodo) async {
}
```

<Callout>

`copyWith` cannot assign `null` to a nullable field: a null argument keeps the current value. Use `copyWithModelFieldValues` instead:

</Callout>

```dart
Future<void> clearTodoDescription(Todo originalTodo) async {
final cleared = originalTodo.copyWithModelFieldValues(
description: ModelFieldValue.value(null),
);

final request = ModelMutations.update(cleared);
final response = await Amplify.API.mutate(request: request).response;
safePrint('Response: $response');
}
```

</InlineFilter>

## Delete an item
Expand Down