Custom model binding, model state, and data annotations

Question

I have a few questions regarding custom model binding, model state, and data annotations.

1) Is it redundant to do validation in the custom model binder if I have da

Answer 1

You will find things work much easier if you inherit from the DefaultModelBinder, override the BindModel method, call the base.BindModel method and then make the manual changes (setting the guid, account name and total time).

1) It is redundant to validate as you have done it. You could write code to reflect the validation metadata much like the default does, or just remove the data annotations validation since you are not using it in your model binder.

2) I don't know, it seems correct, you should step through the code and make sure your custom binder is populating all of the applicable rules.

3) It's a factory for sure, but not so much a constructor.

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EDIT: you couldn't be any closer to the solution, just set the properties you need in the model factory function

public class ProjectModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        if (bindingContext.ModelType == typeof(Project))
        {
            ModelBindingContext newBindingContext = new ModelBindingContext()
            {

                ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(
                    () => new Project()  // construct a Project object
                    {
                        ProjectGuid = System.Guid.NewGuid(),
                        AccountName = controllerContext.HttpContext.User.Identity.Name,
                        // don't set name, thats the default binder's job
                        TotalTime = 0,
                    }, 
                    typeof(Project)         // using the Project metadata
                ),
                ModelState = bindingContext.ModelState,
                ValueProvider = bindingContext.ValueProvider

            };

            // call the default model binder this new binding context
            return base.BindModel(controllerContext, newBindingContext);
        }
        else
        {
            return base.BindModel(controllerContext, bindingContext);
        }
    }

}

Or you could alternately override the CreateModel method:

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, System.Type modelType)
{
    if (modelType == typeof(Project))
    {
        Project model = new Project()
        {
            ProjectGuid = System.Guid.NewGuid(),
            AccountName = controllerContext.HttpContext.User.Identity.Name,
            // don't set name, thats the default binder's job
            TotalTime = 0,
        };

        return model;
    }

    throw new NotSupportedException("You can only use the ProjectModelBinder on parameters of type Project.");
}