CODEWITHSUNDEEP
asp.net-coreasp.net-web-api
iasksillyquestions
iasksillyquestions

Reputation: 5690

Model binding a property attribute not working

I have an ASP.NET Core Web API.

I an endpoint which accepts a model called Search. It has property called Query of type Expression. This Expression object has sub classes.

public class Search {

public Expression Query{get;set;}
}

Public class Expression {
}

public class AndExpression {
  public IList<Expression> Expressions {get;set;}
}

public class MatchesExpression {
  public string FieldId {get;set;}
  public string Value {get;set;}
  public string Operator {get;set;}
}

I post the following JSON to my endpoint (content-type of application/json)

{ "query": { "fieldId": "body", "value": "cake", "operator": "matches" } }

Firstly, the query parameter is just the base Expression - A polymorphic issue!

So... I thought bespoke Model Binder.

I can set up a model binder against the Search object, but you'll note that the AndExpression can contain other Expression objects, so instead I'd like to write a binder that can be bound to "Query" on the Search Model and to Expressions on the AndExpression Model etc etc

I attempted this:

public class Search
{

    [ModelBinder(BinderType = typeof(ExpressionBinder))]
    public Expression Query { get; set; }
}

  public class ExpressionBinder : IModelBinder
    {
        public Task BindModelAsync(ModelBindingContext bindingContext)
        {
            throw new NotImplementedException();
        }
    }




   public class ExpressionBinderProvider : IModelBinderProvider {
    public IModelBinder GetBinder(ModelBinderProviderContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }
    
            if (context.Metadata.ModelType == typeof(Expression))
            {
                return new BinderTypeModelBinder(typeof(ExpressionBinder));
            }
    
            return null;
        }
    }

Ive wired this binder up in the configureServices method of my Startup Class.

I have a break point in the ExpressionBinder and it doesn't hit!

What am I doing wrong?

Also, can I use the [ModelBinder(BinderType = typeof(ExpressionBinder))] attribute against a list of Expressions?

Upvotes: 0

Views: 1756

Answers (1)

iasksillyquestions
iasksillyquestions

Reputation: 5690

So this is very explicit https://github.com/aspnet/Mvc/issues/4553

If a FromBody attribute is applied the ModelBinder attribute wont work!

Upvotes: 4

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