Is there a way to make the ASP.NET Core model binder set properties with private setters?

Question

I use ASP.NET Core minimal APIs and I try to have my view-models (where incoming client data gets mapped to) use private setters for their properties.

But I see that the binding stops working once I make a property have a private setter. Is there any quick fix for this? I would expect this is to be a common requirement and have an easy fix, but I can't find anything online.

Plus, I don't think I am doing anything special :

        public void AddRoutes(IEndpointRouteBuilder app)
        {
            app
                .MapPost("api/document/getById", async ([FromBody] GetDocumentRequest request, [FromServices] ISender sender) =>
                {
                    return await sender.Send(request.Query);
                })
                .WithName("GetDocumentById")
                .Produces<DocumentViewModel>(StatusCodes.Status200OK);
        }

Here, GetDocumentRequest is my view-model.

Answer 1

Since binding here would just deserialize JSON you can mark corresponding properties with JsonIncludeAttribute:

public class GetDocumentRequest
{
    [JsonInclude]
    public int Type { get; private set; }
}

See Non-public members and property accessors section of the docs.

I was hoping for a more global solution, since I plan on having all my properties, for all endpoint view-models, have private setters. And they are too many of them...

Alternatively you can look into customizing JSON contract. Something to get you started:

builder.Services.ConfigureHttpJsonOptions(options => options.SerializerOptions.TypeInfoResolver =
    new DefaultJsonTypeInfoResolver
    {
        Modifiers = { SetAllSetters }
    });

void SetAllSetters(JsonTypeInfo typeInfo)
{
    // find types which need special management
    if (typeInfo.Type.Assembly == typeof(GetDocumentRequest).Assembly)
    {
        var propertyInfos = typeInfo.Type.GetProperties()
            .ToDictionary(pi => pi.Name, StringComparer.InvariantCultureIgnoreCase);
        // todo: check if overriding set method is needed
        foreach (var info in typeInfo.Properties)
        {
            var methodInfo = propertyInfos[info.Name].GetSetMethod(true);
            info.Set = (s, v) => methodInfo.Invoke(s, [v]);
        }
    }
}

Note that this implementation highly likely is less effective compared to the default one. Also I recommend to go through the Use immutable types and properties and consider options provided there (like using constructors or init-only members or records)