Error handling

[ribeiroi]

Hello,
What is the expected way to raise my own errors?

Consider I have a GraphQL query that returns Person. My C# resolver is defined like this:
public static async Task<Person> GetPerson(int personId)

If I want to raise an error, let's say personId is not within a range, I could throw new Exception("personId not in expected range"), however the GraphQL response .Errors (of type GraphQLError[]) mix a simple custom error message with a lot of technical stuff (locations, path, extensions, etc.):
{"errors":[{"message":"Error trying to resolve field \u0027getPerson\u0027.","locations":[{"line":3,"column":9}],"path":["getPerson"],"extensions":{"code":"","codes":[""],"details":"GraphQL.Execution.UnhandledError: Error trying to resolve field \u0027getPerson\u0027.\r\n ---\u003E System.Exception: personId not in expected range...

I also tried to throw new GraphQLError but the constructor is empty (would still have same issue as above anyway).
I'm thinking that the GraphQLError is not really suitable for handled/custom errors. Am I right?

What I know that worked well is to wrap Person with a custom class like ResultCall (Task<ResultCall<Person>>) where I can have my own error property (along with the data, of course). Is this an acceptable solution to send my own error messages, or should I always use the .Errors (GraphQLError[]) property?

Having a wrapper means the client have first to check GraphQL's .Errors, then check my own ResultCall .Errors.

If I should use the GraphQL .Errors, then what is the recommended approach as throwing an Exception does not seem appropriate.

Thank you.

[rose-a]

Hi, the error format is specified in the GraphQL spec with a mandatory error message field. The other fields heavily depend on the server implementation. Since GraphQL was born in the Javascript world it is not always straight forward to transfer the concepts from the spec into the C# language.

GraphQLError does not inherit from Exception and thus cannot be thrown directly...

If you want to work with an Exception the easiest way would be to create a GraphQLErrorException which takes the GraphQLError[] array as a constructor parameter and throw that in your GetPerson method. You could build yourself an extension method following the example of HttpResponseMessage.EnsureSuccessStatusCode which reduces this to a simple method call on the result.
Handling HTTP status codes is a similar "paradigm shift" by the way...

If you need to act differently depending on the actual error, then you need to check how your server responds in different error conditions and build your error handling specifically for your use case and your server.

If you control the server it might be possible to extend the errors with custom content, so you can "recreate" an exception which has ocurred on the server from the contents of a GraphQLError (I'm doing that a lot using graphql-dotnet/server

[ribeiroi]

Thank you. Thanks to a colleague, we found out that throw new ExecutionError(...) actually works, it puts the message parameter in the message field output of the GraphQLError (instead of burying it inside the details field) as shown in the original post.