Entity Framework error when submitting empty fields

Question

VS 2010 Beta 2, .NET 4.

In my ASP.NET MVC 2 application, when I submit a form to an action method that accepts an object created by the entity framework, I get the following error:

Exception Details: System.Data.ConstraintException: This property cannot be set to a  
null value.

Source Error: 


Line 4500:                OnTextChanging(value);
Line 4501:                ReportPropertyChanging("Text");
Line 4502:                _Text = StructuralObject.SetValidValue(value, false);
Line 4503:                ReportPropertyChanged("Text");
Line 4504:                OnTextChanged();

The property is called "Text" and is of type "text NOT NULL" in MS SQL 2008.

My action will check if the value is nullorempty, if it is, a model error will be added, but I get the error as soon as I submit the form.

Answer 1

Are you binding directly to the entity? Sure looks like it. So you have two choices:

1. Write a custom model binder which translates null -> empty string.
2. Bind to an edit model which allows nulls instead, and then change this to empty string when you copy the values to the entity in the action.

I'd choose #2, personally. I think you should always use view/edit models, and this is a great example of why.

Answer 2

Is this an issue with the MVC2 and Entity Framework 4 or is this by design? It appears that validation of EF properties works fine for datetime non-nullable (required) fields and data type validation of numeric versus string fields is working without having to use ViewModels.

I recreated the issue using with a simple FOOBAR table using a single, non-nullable varchar(50) column called barName in slq 2008. I generated the EF model from that database and quickly added a controller and a CREATE view for the FOOBAR entity. If I try to POST to the CREATE action without entering in a value for the property barName, VS steps into an exception within the designer.cs file of the model (just like the one above). When, I try to step past the exception, the validation message shows up on the form and the field is highlighted in pink.

It seems like something is not firing in the correct sequence. Because the exception occurs before VS steps into the HTTPPOST CREATE method.

I found the code from the ASP.Net MvcMusicStore sample helpful. http://mvcmusicstore.codeplex.com/releases/view/44445#DownloadId=119336

It appears that binding to the ViewModel fixes the issue.

namespace MvcMusicStore.ViewModels { public class StoreManagerViewModel { public Album Album { get; set; } public List Artists { get; set; } public List Genres { get; set; } } } ........

namespace MvcMusicStore.Models
{
    [MetadataType(typeof(AlbumMetaData))]
    public partial class Album
    {
        // Validation rules for the Album class

        [Bind(Exclude = "AlbumId")]
        public class AlbumMetaData
        {
            [ScaffoldColumn(false)]
            public object AlbumId { get; set; }

            [DisplayName("Genre")]
            public object GenreId { get; set; }

            [DisplayName("Artist")]
            public object ArtistId { get; set; }

            [Required(ErrorMessage = "An Album Title is required")]
            [StringLength(160)]
            public object Title { get; set; }

            [DisplayName("Album Art URL")]
            [StringLength(1024)]
            public object AlbumArtUrl { get; set; }

            [Required(ErrorMessage = "Price is required")]
            [Range(0.01, 100.00, ErrorMessage="Price must be between 0.01 and 100.00")]
            public object Price { get; set; }
        }
    }
}

Answer 3

I was having the same problem. I looked around and found a work around here. It describes the problem as being caused by the EF validation taking place before the Required field validation. It also shows how we can work around this problem by using a [DisplayFormat] Tag. Hope this will help you.

Here's the link to the question and the workaround:

http://stackoverflow.com/questions/3129080/server-side-validation-of-a-required-string-property-in-mvc2-entity-framework-4-d