Expected non-null value, resolve delegate return null

[mike-niemand]

Hi All,

This is no doubt related to: #807

When executing a query e.g. {menu: {menuId, nenuName}} the document executor throws:

Expected non-null value, resolve delegate return null for $GraphQL.Types.ComplexGraphType`1[DelFornoAPI.Models.Customer]

This type is unrelated to the query but does exist as a field in another type i.e.:

 public class CustomerOrderType : ObjectGraphType<VMCustomerOrder>
    {
        public CustomerOrderType()
        {
            Name = "CustomerOrderType";
            Field(x => x.CustomerOrderId);
            Field(x => x.FranchiseId);
            Field(x => x.Instruction, true, typeof(StringGraphType));
            Field(x => x.Customer, true, typeof(ComplexGraphType<Customer>));
        }
    }

It is however set to allow nullable.

Why is it attempting to validate this type as not null when it is unrelated to the query?

[joemcbride]

Field(x => x.Customer, true, typeof(ComplexGraphType<Customer>));

This won't work. ComplexGraphType is an abstract base type. Arguably that perhaps should be an internal type. You need to create a class that inherits from ObjectGraphType.

[mike-niemand]

Thanks for the response Joe, it's much appreciated. I'm still having trouble even after defining Customer as typeof ObjectGraphType.

_{System.InvalidOperationException: Expected non-null value, resolve delegate return null for "$GraphQL.Types.ObjectGraphType`1[DelFornoAPI.Models.Customer]"
   at GraphQL.GraphQLExtensions.BuildNamedType(Type type, Func`2 resolve)
   at GraphQL.Types.GraphTypesLookup.HandleField(Type parentType, FieldType field, TypeCollectionContext context)
   at GraphQL.Types.GraphTypesLookup.AddType(IGraphType type, TypeCollectionContext context)
   at GraphQL.Types.GraphTypesLookup.Create(IEnumerable`1 types, IEnumerable`1 directives, Func`2 resolveType, IFieldNameConverter fieldNameConverter)
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at GraphQL.Types.Schema.get_AllTypes()
   at GraphQL.Instrumentation.FieldMiddlewareBuilder.ApplyTo(ISchema schema)
   at GraphQL.DocumentExecuter.ExecuteAsync(ExecutionOptions options)}_

I'm not querying this type at all though?

[joemcbride]

That stacktrace is helpful. This is happening during the initialization of the Schema, which builds up the entire Graph.

Does your customer class look like this? You didn’t just do typeof(ObjectGraphType<Customer>)?

public class CustomerGraphType : ObjectGraphType<Customer>
{
  public CustomerGraphType()
  {
    Name = “Customer”;
    // add fields
  }
}

[mike-niemand]

I have the following registered in the schema:

public class CustomerType : ObjectGraphType<Customer>
    {
        public CustomerType()
        {
            Name = "Customer";
            Field(x => x.CustomerId);
            Field(x => x.Firstname);
            Field(x => x.Surname);
        }
    }

and

public class CustomerOrderType : ObjectGraphType<CustomerOrder>
    {
        public CustomerOrderType()
        {
            Name = "CustomerOrderType";
            Field(x => x.CustomerOrderId);
            Field(x => x.FranchiseId);
            Field(x => x.Customer, true, typeof(ObjectGraphType<CustomerType>));
        }
    }

Which throws:

_{GraphQL.ExecutionError: Expected non-null value, resolve delegate return null for "$GraphQL.Types.ObjectGraphType`1[DelFornoAPI.GraphQL.CustomerType]" ---> System.InvalidOperationException: Expected non-null value, resolve delegate return null for "$GraphQL.Types.ObjectGraphType`1[DelFornoAPI.GraphQL.CustomerType]"
   at GraphQL.GraphQLExtensions.BuildNamedType(Type type, Func`2 resolve)
   at GraphQL.Types.GraphTypesLookup.HandleField(Type parentType, FieldType field, TypeCollectionContext context)
   at GraphQL.Types.GraphTypesLookup.AddType(IGraphType type, TypeCollectionContext context)
   at GraphQL.Types.GraphTypesLookup.Create(IEnumerable`1 types, IEnumerable`1 directives, Func`2 resolveType, IFieldNameConverter fieldNameConverter)
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at GraphQL.Types.Schema.get_AllTypes()
   at GraphQL.Instrumentation.FieldMiddlewareBuilder.ApplyTo(ISchema schema)
   at GraphQL.DocumentExecuter.ExecuteAsync(ExecutionOptions options)_

I'm clearly confused as I don't understand why it's expected to be non-null?

[joemcbride]

Change this:

Field(x => x.Customer, true, typeof(ObjectGraphType<CustomerType>));

To this:

Field(x => x.Customer, true, typeof(CustomerType));

[mike-niemand]

Yes. That solved it and also taught me a little more about what you've done. Thank-you so much. What a great project.

[joemcbride]

One thing that could perhaps be done is to throw an error if you pass an object that inherits from IGraphType to the ObjectGraphType/ComplexGraphType generic argument.

[mike-niemand]

I'm sure that would help. Was this a change implemented in 2.x? I had it working fine before I moved to 2.4 although this is a much better.

[joemcbride]

I'm not sure. That should have never worked. That it somehow was is a mystery to me.

[sungam3r]

@mike-niemand Is this issue still actual?

[mike-niemand]

@mike-niemand Is this issue still actual?

I don't have this issue anymore.