ASP.NET Core - ModelBinder - 集合 - 陷入无限/无限循环

Question

I am facing an issue with custom ModelBinder ( IModelBinder implementation).

This is a model I am trying to bind from query string. The example parameter looks like this:

?Where.Name[eq]=Jakub

The class I am trying bind to is this:

[MetadataFilterBinder]
public class MetadataFilter
{
    public string Term { get; set; }

    public string Field { get; set; }

    public FilterClause Clause { get; set; }

    // Where.Name[eq]=Jakub
    public static bool TryParse(string s, out MetadataFilter metadataFilter)
    {
        // commented out for brevity
    }
}

My attribute annotating this model binder is:

public class MetadataFilterBinderAttribute : ModelBinderAttribute
    {
        public MetadataFilterBinderAttribute() : base(typeof(MetadataFilterBinder))
        {
            BindingSource = BindingSource.Query;
        }
    }

The ModelBinder implementation:

public class MetadataFilterBinder : IModelBinder
    {
        public Task BindModelAsync(ModelBindingContext bindingContext)
        {
            if (bindingContext == null)
                throw new ArgumentNullException(nameof(bindingContext));

            var modelName = bindingContext.ModelName;

            var queryStringKeyName = new string(modelName.Where(char.IsLetter).ToArray());

            var whereKeyValue = bindingContext.HttpContext.Request.Query
                .FirstOrDefault(q => q.Key.StartsWith($"{queryStringKeyName}.", StringComparison.InvariantCultureIgnoreCase));

            if (whereKeyValue.Key == string.Empty)
                return Task.CompletedTask;

            var valueProviderResult = bindingContext.ValueProvider.GetValue(whereKeyValue.Key);
            if (valueProviderResult == ValueProviderResult.None)
                return Task.CompletedTask;

            bindingContext.ModelState.SetModelValue(modelName, valueProviderResult);

            if (string.IsNullOrEmpty(valueProviderResult.FirstValue))
                return Task.CompletedTask;
            var result = MetadataFilter.TryParse($"{whereKeyValue.Key}={whereKeyValue.Value}", out var metadataFilter);
            if (result)
            {
                bindingContext.Result = ModelBindingResult.Success(metadataFilter);
            }
            else
            {
                bindingContext.ModelState.TryAddModelError(modelName, "Invalid metadata filter value.");
            }
            
            return Task.CompletedTask;
    }
}

The MetadataFilter class resides in following model that should be bound from QueryString.

public class Metadata : IMetadataPaginable, IMetadataSortable, IMetadataFilterable
    {
        public MetadataPaging Paging { get; set; }

        public MetadataSort Sort { get; set; }

        public IReadOnlyCollection<MetadataFilter> Where { get; set; }
    }

Now my code and ModelBinder get's executed correctly and all is getting set correctly. I set ModelBindingResult & returning Task.Completed . However it get stuck in an endless loop that I have no idea how to indicate that it should stop.

The BindModelAsync method gets called infinite amount of times until it hits the limit. The ModelName keeps incrementing as "Where[0]" , "Where[1]" , "Where[2]" , "Where[n]".

How can I let the Binder know that I am good and that I've bound all the items I needed?

Note this is not a duplicate of Inifinite loop during model binding when using [ModelBinder] attribute

Answer 1

I solved this by putting the ModelBinder attribute on the model property . So my Binder instead of trying to bind each item individually which triggers the endless loop, it binds the whole collection at once and that's when this issue disappears.

Final result: