清理ASP.Net Core 2.2中的参数

Question

I have a seemingly rather specific problem. My top-level controller and models for complex parameters are auto-generated (Nswag). Some of the model consists of enums. I have parameters (in query or body) which have to contain backslashes. The values of these in the auto-generated enums automatically have backslashes replaced with underscores. To make model validation work, I have to somehow catch parameters binding with these enums and change them before binding occurs therefore.

For example, given a query

?param=A\\B

(or a body with param="a\\b" ) and the Enum:

public enum SomeEnum
{
  [System.Runtime.Serialization.EnumMember(Value = @"A\B")]
  A_B = 0
}

Model validation fails because A\\B isn't found in the enum, naturally.

I have tried filters, custom model binders etc. and custom model binding seems to be the best place as it can be made to apply at precisely the point of binding that specific model. Now, the problem is that I need to modify the incoming parameter and bind to a modified version with underscores. I can't for the life of me find out how to do this. I implemented a custom IModelBinder class, which is called properly but ModelBindingResult.Success(model) doesn't alter what is bound to .

Just to be clear, this has nothing to do with URL encoding or binding to collections etc. This is all working fine.

I essentially need to modify parameters being bound with a specific Enum so that they match the auto-generated enum properties. Any ideas much appreciated.

Answer 1

It seems that a custom binder is the correct way to do it, when you code it properly ... Below is the binder class that works nicely. SSASPropertyNameBinder is the enum whose values can contain backslashes. This class is mostly boiler plate from the MS ASP.Net Core docs on custom model binders - the interesting bit is at the end.

public class SSASPropertyNameBinder : IModelBinder
{

    public Task BindModelAsync(ModelBindingContext bindingContext)
    {
        if (bindingContext == null)
        {
            throw new ArgumentNullException(nameof(bindingContext));
        }

        var modelName = bindingContext.ModelName;

        // Try to fetch the value of the argument by name
        var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);

        if (valueProviderResult == ValueProviderResult.None)
        {
            return Task.CompletedTask;
        }

        var value = valueProviderResult.FirstValue;

        // Check if the argument value is null or empty
        if (string.IsNullOrEmpty(value))
        {
            return Task.CompletedTask;
        }

        ValueProviderResult newValueProviderResult = new ValueProviderResult(valueProviderResult.FirstValue.Replace(@"\", "_"));
        bindingContext.ModelState.SetModelValue(modelName, newValueProviderResult);
        SSASServerPropertyName spn;

        // Check if a valid SSAS property
        if (Enum.TryParse<SSASServerPropertyName>(newValueProviderResult.FirstValue, out spn))
        {
            bindingContext.Result = ModelBindingResult.Success(spn);
        }
        else
        {
            bindingContext.ModelState.TryAddModelError(modelName, $"Invalid SSAS Property: {valueProviderResult.FirstValue}");
        }

        return Task.CompletedTask;
    }
}