ListNestedAttribute can't be set to Computed in Resource

[tom-ludwig]

Module version

github.com/hashicorp/terraform-plugin-framework v1.14.1

Relevant provider source code

type parentObject struct {
     someFields....
     ListNested []nestedObjectModel `tfsdk:"nestedList"`

			"nestedList": schema.ListNestedAttribute{
				Computed: true, <----- PROBLEM
				NestedObject: schema.NestedAttributeObject{
					Attributes: getNestedObjectSchema(),
				},
			},

Expected Behavior

The nestedList field should behave exactly like in the datasource.

Actual Behavior

An error is thrown:

____.go:222: Step 1/2 error: Error running apply: exit status 1

        Error: Value Conversion Error

          with ___.___,
          on terraform_plugin_test.tf line 12, in resource "____" "_____":
          12: resource "______" "________" {

        An unexpected error was encountered trying to build a value. This is always
        an error in the provider. Please report the following to the provider
        developer:

        Received unknown value, however the target type cannot handle unknown values.
        Use the corresponding `types` package type or a custom type that handles
        unknown values.

        Path: nestedList
        Target Type: []provider.nestedObjectModel
        Suggested Type: basetypes.ListValue

Steps to Reproduce

Try to mark a listNestedAttribute, as computed...

References

[ansgarm]

Hi @tom-ludwig 👋

Thank you for reporting this! Could you share the definition of provider.nestedObjectModel so I have a more complete example to try to reproduce this?

Thanks in advance!

[tom-ludwig]

Hey @ansgarm ,
Apologies for the wait. I've put together a better example for you—hope it makes things clearer!
Let me know if you have any questions.

// Typically in another file
type carResourceModel struct {
	ID    types.String `tfsdk:"id"`
	Model types.String `tfsdk:"model"`
}

func getCarResourceSchema() map[string]schema.Attribute {
	return map[string]schema.Attribute{
		"id": schema.StringAttribute{
			Computed: true,
		},
		"model": schema.StringAttribute{
			Computed: true,
		},
	}
}

var (
	_ resource.Resource              = &instanceResource{}
	_ resource.ResourceWithConfigure = &instanceResource{}
)

type personResource struct{}

type personResourceModel struct {
	ID   types.String `tfsdk:"id"`
	Name types.String `tfsdk:"name"`
	Cars types.List   `tfsdk:"cars"` // <-- I'd much rather use carResourceModel here.
}

func (r *personResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
	resp.Schema = schema.Schema{
		Attributes: map[string]schema.Attribute{
			"id": schema.StringAttribute{
				Computed: true,
			},
			"name": schema.StringAttribute{
				Required: true,
			},
			"cars": schema.ListNestedAttribute{
				Computed: true,
				NestedObject: schema.NestedAttributeObject{
					Attributes: getCarResourceSchema(),
				},
			},
		},
	}
}

// Function to map a person model to resource state.
func mapPersonToResourceState(ctx context.Context, person *model.Person, state *personResourceModel) error {
         // <--- Needed Implementation --->
	resourceDataCarTypes := map[string]attr.Type{
		"id":    types.StringType,
		"model": types.StringType,
	}

	newCars := make([]carResourceModel, len(person.Cars))
	for i, item := range person.Cars {
		mapCarToResourceState(&item, &newCars[i])
	}

	var diags diag.Diagnostics
	state.Cars, diags = types.ListValueFrom(ctx, types.ObjectType{AttrTypes: resourceDataCarTypes}, newCars)

	if diags.HasError() {
		return fmt.Errorf("error mapping cars to state: %s", diags.Errors())
	}
         // <--- Wanted Implementation --->
        state.Cars = mapCarsToResourceState(person.Cars) // Returns []resourceCarModel
        // <--- END --->
	state.ID = types.StringValue(person.ID)

	return nil
}

// mapCarToResourceState definition is present