Question

I have an entityframework entity called “ABC” (attributes ID and Title).

On update record view, I have added the ID as hidden field and title is the text box.

Controller looks like something:

public ActionResult UpdateAction( ABC obj )

I get everything fine and fair in obj – i.e., the title, and the ID.

Now to update the record in database, I read the original entity:

var original = (from x in base.context.ABC where x.id == obj.id ).Single();

Now to reflect the changes in original, I think should do the update model:

this.TryUpdateModel( original );

I get an error 😐 … stating that column ID cannot be changed.

The property 'id' is part of the object's key information and cannot be modified. 

I do not want to manually assign the properties back to original object.

The other alternative can be:

TryUpdateModel(original, new string[] { "Title" }, form.ToValueProvider());

But I hate strings – also, my object has like 20 attributes 😐

Can someone please suggest a better pattern of doing so?

Rgds

Answer 1

public class ControllerExt : Controller
{
    protected void UpdateModel<TModel>(TModel model, params Expression<Func<TModel, object>>[] property) where TModel : class
    {
        var props = new List<string>(property.Length);
        foreach (var p in property)
        {
            var memberExpression = RemoveUnary(p.Body) as MemberExpression;
            if (memberExpression == null)
            {
                throw new NullReferenceException("Can not retrieve info about member of {0}".FormatThis(typeof(TModel).Name));
            }
            props.Add(memberExpression.Member.Name);
        }
        this.UpdateModel(model, props.ToArray());
    }

    private static Expression RemoveUnary(Expression body)
    {
        var unary = body as UnaryExpression;
        if (unary != null)
        {
            return unary.Operand;
        }
        return body;
    }
}

Example:

UpdateModel<MyModel>(model, x => x.PropertyFromMyModel_1, x => x.PropertyFromMyModel_2);