Fixing ResolveAsync In EntityGraphQL Top-Level Services

by Alex Johnson 56 views

When working with EntityGraphQL, you might encounter issues with ResolveAsync when dealing with top-level services. This article dives into common problems, specifically focusing on scenarios where ResolveAsync doesn't seem to work as expected. We'll explore a practical example, discuss the symptoms, and provide insights into potential solutions. Understanding these nuances can significantly improve your experience with EntityGraphQL and ensure your queries function correctly.

The Case of the Misbehaving ResolveAsync

Let's start by examining a real-world scenario. A developer encountered issues while trying to use ResolveAsync for top-level services in their EntityGraphQL setup. The problem manifested in two primary ways:

  1. TestTopLevelAsyncService: Returned unexpected data where each field seemed to represent the entire object, rather than the individual properties.
  2. TestTopLevelAsyncServiceList: Threw an exception related to the SelectWithNullCheck method, indicating a mismatch in type arguments.

To better understand the context, let's dissect the code snippet provided. This will help us identify the root cause of the issues and explore potential fixes.

Dissecting the Code: A Deep Dive

The code includes two primary test cases: TestTopLevelAsyncService and TestTopLevelAsyncServiceList. Both tests aim to validate the functionality of ResolveAsync with top-level services, but they exhibit different problems.

TestTopLevelAsyncService: The Curious Case of the Object Fields

In the TestTopLevelAsyncService test, the goal is to retrieve a single Project object using ResolveAsync. The code defines a ContextTest class with an asynchronous method GetProject that returns a Task<Project>. This method simulates fetching a project from a data source. Let's look at the key parts of the code:

public class ContextTest
{
    public async Task<Project> GetProject()
    {
        return await System.Threading.Tasks.Task.FromResult(new Project() {  Id = 1, Name = "test", CreatedBy = 1 });
    }
}

[Fact]
public void TestTopLevelAsyncService()
{
    var schema = SchemaBuilder.FromObject<TestDataContext>();

    // Here the expression project is extracted and the expression is used for a field name, which is a duplicate of the project field
    schema.Query().AddField("getProject", "Something").ResolveAsync<ContextTest>((context, us) => us.GetProject());

    var gql = new QueryRequest
    {
        Query =
            @"{
              getProject { id name createdBy }
            }",
    };

    var context = new TestDataContext();
   
    var serviceCollection = new ServiceCollection();       
    serviceCollection.AddSingleton(new ContextTest());
    serviceCollection.AddSingleton(context);

    var res = schema.ExecuteRequest(gql, serviceCollection.BuildServiceProvider(), null);
    Assert.Null(res.Errors);
    Assert.NotNull(res.Data);
    dynamic project = res.Data["getProject"]!;
    Assert.Equal(1, project.id);
    Assert.Equal("Project 1", project.name);
    Assert.Equal(1, project.createdBy);
}

The critical part here is the schema.Query().AddField("getProject", "Something").ResolveAsync<ContextTest>((context, us) => us.GetProject()); line. This code configures EntityGraphQL to resolve the getProject field by calling the GetProject method on an instance of ContextTest. The service is registered as a singleton in the ServiceCollection. However, the test results show that the fields (id, name, createdBy) are not being populated correctly. Instead, they seem to contain the entire Project object. This suggests an issue with how EntityGraphQL is handling the resolution of the asynchronous task.

TestTopLevelAsyncServiceList: The Exception Conundrum

The TestTopLevelAsyncServiceList test aims to retrieve a list of Project objects. Similar to the previous test, it defines an asynchronous method GetProjects in the ContextTest class, which returns a Task<IEnumerable<Project>>. Let's break down the code:

public class ContextTest
{
    public async Task<IEnumerable<Project>> GetProjects()
    {
        return await System.Threading.Tasks.Task.FromResult(new[] { new Project() { Id = 1, Name = "test", CreatedBy = 1 } });
    }
}

[Fact]
public void TestTopLevelAsyncServiceList()
{
    var schema = SchemaBuilder.FromObject<TestDataContext>();

    // Here the expression project is extracted and the expression is used for a field name, which is a duplicate of the project field
    schema.Query().AddField("getProjects", "Something").ResolveAsync<ContextTest>((context, us) => us.GetProjects());

    var gql = new QueryRequest
    {
        Query =
            @"{
              getProjects { id name createdBy }
            }",
    };

    var context = new TestDataContext();

    var serviceCollection = new ServiceCollection();
    serviceCollection.AddSingleton(new ContextTest());
    serviceCollection.AddSingleton(context);

    var res = schema.ExecuteRequest(gql, serviceCollection.BuildServiceProvider(), null);
    Assert.Null(res.Errors);
    Assert.NotNull(res.Data);
    dynamic project = res.Data["getProjects"]!;
    Assert.Equal(1, project.id);
    Assert.Equal("Project 1", project.name);
    Assert.Equal(1, project.createdBy);
}

The key line here is schema.Query().AddField("getProjects", "Something").ResolveAsync<ContextTest>((context, us) => us.GetProjects());. This sets up the resolution for the getProjects field using the GetProjects method. However, this test throws an exception:

Field 'getProjects' - No generic method 'SelectWithNullCheck' on type 'EntityGraphQL.Extensions.EnumerableExtensions' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.

This exception indicates a problem within EntityGraphQL's internal handling of asynchronous enumerable results. The SelectWithNullCheck method, likely used to process the list of projects, is failing due to a type mismatch or an incorrect method signature.

Identifying the Root Causes

Based on the symptoms and the code, we can pinpoint a few potential root causes:

  1. Incorrect Asynchronous Handling: EntityGraphQL might not be correctly unwrapping the asynchronous results from ResolveAsync, leading to the entire object being passed as a field value in TestTopLevelAsyncService.
  2. Type Mismatch in Enumerable Processing: The exception in TestTopLevelAsyncServiceList suggests a type mismatch during the processing of the asynchronous enumerable result. The SelectWithNullCheck method might be expecting a different type or encountering a null value unexpectedly.
  3. Service Resolution Issues: Although less likely, there could be subtle issues in how the services are being resolved and injected into the resolvers.

Strategies for Resolution

To address these issues, consider the following strategies:

1. Verify Asynchronous Result Handling

Ensure that EntityGraphQL correctly handles asynchronous results. This might involve checking the version of EntityGraphQL you are using and reviewing the documentation for any known issues or updates related to asynchronous resolvers. You might also want to simplify the resolver logic to isolate the problem. For example, you could try returning a simple hardcoded result to see if the basic asynchronous resolution is working.

2. Inspect Type Mismatches

The exception in TestTopLevelAsyncServiceList points to a type mismatch. Investigate the SelectWithNullCheck method and the types it operates on. Ensure that the types being passed to this method are consistent with its expectations. This might involve debugging EntityGraphQL's internal code or adding logging to trace the types at runtime.

3. Review Service Registration

Double-check how the services are being registered and resolved. Ensure that the ContextTest and TestDataContext are correctly registered in the ServiceCollection and that they are being injected into the resolvers as expected. Incorrect service registration can lead to unexpected behavior and exceptions.

4. Provide Explicit Type Information

In some cases, providing explicit type information can help EntityGraphQL correctly handle the results. For example, you could try explicitly specifying the return type of the ResolveAsync method:

schema.Query().AddField("getProjects", "Something").ResolveAsync<ContextTest, IEnumerable<Project>>((context, us) => us.GetProjects());

5. Update EntityGraphQL

Ensure you are using the latest version of EntityGraphQL. Newer versions often include bug fixes and improvements that address issues like these. Check the EntityGraphQL release notes for any relevant fixes or updates.

6. Community Support and Issue Reporting

If you've exhausted the above strategies and are still facing issues, consider reaching out to the EntityGraphQL community for support. You can also report the issue on the EntityGraphQL GitHub repository, providing detailed information about the problem, your code, and the steps you've taken to troubleshoot it. This can help the maintainers identify and address the issue in future releases.

Practical Steps for Debugging

To effectively debug these issues, consider the following steps:

  1. Simplify the Query: Start with a very basic query that only requests a few fields. This helps isolate the problem and rule out issues with complex queries.
  2. Add Logging: Add logging statements within your resolvers and within EntityGraphQL's internal code (if possible) to trace the execution flow and inspect the values of variables.
  3. Use Debugging Tools: Utilize your IDE's debugging tools to step through the code and inspect the state of variables at runtime.
  4. Create Minimal Reproducible Examples: If you're reporting an issue, create a minimal, self-contained example that reproduces the problem. This makes it easier for others to understand and address the issue.

Conclusion

Troubleshooting ResolveAsync issues in EntityGraphQL top-level services requires a systematic approach. By understanding the potential root causes, applying the strategies outlined in this article, and utilizing effective debugging techniques, you can resolve these issues and ensure your EntityGraphQL queries function correctly. Remember to stay updated with the latest EntityGraphQL releases and engage with the community for support when needed.

For further reading and resources on EntityGraphQL, you can check out the official documentation and community forums. You might find helpful information and examples on the official EntityGraphQL documentation. This resource provides in-depth explanations and guides to help you master EntityGraphQL.