Complete example of adding custom Operation

[gojanpaolo]

Hello! I am trying to follow how to add a custom operation as described on Extending Filtering. Unfortunately, there seems to be some missing/outdated pieces to completely add the CustomOperations.Like in the example.

I'll probably revisit this next week and will likely look into HC source code to figure out how the built-in operations are added. But I'm hoping someone can share a complete working sample of adding a custom operation before I get to revisit it again. Thanks!

[gojanpaolo]

I think I got it.. What's missing was Type<StringType>().Extend().OnBeforeCreate(_ => _.Handler = ...) to fully configure the custom operation.

public static class CustomOperations
{
    public const int Like = 1025;
}

public class CustomFilteringConvention : FilterConvention
{
    protected override void Configure(IFilterConventionDescriptor descriptor)
    {
        descriptor.AddDefaults();
        descriptor
            .Operation(CustomOperations.Like)
            .Name("like");
        descriptor
            .Configure<StringOperationFilterInputType>(_ => _
                .Operation(CustomOperations.Like)
                .Type<StringType>()
                .Extend()
                .OnBeforeCreate(_ => _.Handler = new QueryableStringInvariantEqualsHandler()));
    }
}

// from https://chillicream.com/docs/hotchocolate/api-reference/extending-filtering/#extending-iqueryable
// but only applied to `like` custom operation as shown above
public class QueryableStringInvariantEqualsHandler : QueryableStringOperationHandler
{
    private static readonly MethodInfo _toLower = typeof(string)
        .GetMethods()
        .Single(
            _ => _.Name == nameof(string.ToLower) &&
            _.GetParameters().Length == 0);

    protected override int Operation => CustomOperations.Like;

    public override Expression HandleOperation(
        QueryableFilterContext context,
        IFilterOperationField field,
        IValueNode value,
        object parsedValue)
    {
        var property = context.GetInstance();
        var str = (string)parsedValue;
        return Expression.Equal(
            Expression.Call(property, _toLower),
            Expression.Constant(str.ToLower()));
    }
}

// in Startup.ConfigureServices
services
.AddGraphQLServer()
.AddConvention<IFilterConvention, CustomFilterConvention>()
.AddFiltering()

[PascalSenn]

Hi @gojanpaolo

You are very close! I do see the need for a custom example. I thought there was one actually, but it just overrides a build in handler.

Instead of setting the Handler directly you can also use a provider extension:

public class CustomFilteringConvention : FilterConvention
{
    protected override void Configure(IFilterConventionDescriptor descriptor)
    {
        descriptor.AddDefaults();
        descriptor
            .Operation(CustomOperations.Like)
            .Name("like");
            
        descriptor
            .Configure<StringOperationFilterInputType>(_ => _
                .Operation(CustomOperations.Like)
                .Type<StringType>());
                
        descriptor.AddProviderExtension(
                new QueryableFilterProviderExtension(
                    y => y.AddFieldHandler<QueryableStringInvariantEqualsHandler>());
    }
}

[gojanpaolo]

Nice! That looks more consistent with the other configuration and not as hacky as the Extend().OnBeforeCreate.

At first, I got confused on how QueryableStringInvariantEqualsHandler was linked CustomOperations.Like but it looks like it's because of the protected override int Operation => CustomOperations.Like in QueryableStringInvariantEqualsHandler.