Question

I am experiencing a very frustrating issue when trying to insert a new record
using LINQ to SQL. If I step through this code sometimes it inserts the new record
but most of the time it doesn’t. When it fails I seeing the following error.

Cannot insert the value NULL into
column ‘Name’, table
‘EquipmentManufacturer’; column does
not allow nulls. INSERT fails. The
statement has been terminated.

This error is complaining about the ‘Name’ field being null but that should not be the case. When I debug and step through this collection[“Name”] has the value I entered on the form.

Here is the table create statement.

CREATE TABLE [EquipmentManufacturer] (
  [EquipmentManufacturerID] [int] IDENTITY(1,1) NOT NULL,
  [Name] [nvarchar](50) NOT NULL,

 CONSTRAINT [PK_EquipmentManufacturer] PRIMARY KEY CLUSTERED 
 (
    [EquipmentManufacturerID] ASC
 ) ON [PRIMARY]
) ON [PRIMARY]

Here is the ASP.NET MVC Controller and Create Action where I am trying to add a new record.

public partial class EquipmentManufacturerController : Controller
{
  private IRepository<EquipmentManufacturer> reposManu;

  // POST: /EquipmentManufacturer/Create
  [AcceptVerbs(HttpVerbs.Post)]
  public virtual ActionResult Create(FormCollection collection)
  {
    EquipmentManufacturer entity = reposManu.New();
    try
    {
      //HACK: Something screwy is going on here the entity oject doesn't always get updated correctly
      //UpdateModel(entity);

      entity.Name = collection["Name"];
      reposManu.Insert(entity);
      reposManu.SubmitChanges();

      return RedirectToAction("Details", new { id = entity.EquipmentManufacturerID });
    }
    catch (RulesException ex)
    {
      ex.AddModelStateErrors(ModelState, "EquipmentManufacturer");
      return ModelState.IsValid ? RedirectToAction("Create")
        : (ActionResult)View();
    }
  }
}

Here is the Create.aspx view.

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">

    <h2>Create</h2>

    <%= Html.ValidationSummary("Create was unsuccessful. Please correct the errors and try again.") %>

    <% using (Html.BeginForm()) {%>

        <fieldset>
            <legend>Fields</legend>
            <p>
                <label for="Name">Name:</label>
                <%= Html.TextBox("Name") %>
                <%= Html.ValidationMessage("Name") %>
            </p>
            <p>
                <input type="submit" value="Create" />
            </p>
        </fieldset>

    <% } %>
    <%= Html.ClientSideValidation<EquipmentManufacturer>() %>

    <div>
        <%=Html.ActionLink("Back to List", "Index") %>
    </div>

</asp:Content>

Here is the Repository implementation I am using.

public class Repository<T> : IRepository<T> where T : class
{
  public IDataContext DC { get; set; }

  public Repository(IDataContext dataContext)
  {
      DC = dataContext;
  }

  /// <summary>
  /// Return all instances of type T.
  /// </summary>
  /// <returns></returns>
  public IEnumerable<T> All()
  {
      return GetTable;
  }

  /// <summary>
  /// Return all instances of type T that match the expression exp.
  /// </summary>
  /// <param name="exp"></param>
  /// <returns></returns>
  public IQueryable<T> Find(Expression<Func<T, bool>> exp)
  {
      return GetTable.Where<T>(exp);
  }

  /// <summary>See IRepository</summary>
  /// <param name="exp"></param>
  /// <returns></returns>
  public T Single(Expression<Func<T, bool>> exp)
  {
      return GetTable.SingleOrDefault(exp);
  }

  /// <summary>See IRepository</summary>
  /// <param name="exp"></param>
  /// <returns></returns>
  public T First(Expression<Func<T, bool>> exp)
  {
      return GetTable.First(exp);
  }

  /// <summary>See IRepository</summary>
  /// <param name="entity"></param>
  public virtual void Delete(T entity)
  {
      DC.Context.GetTable<T>().DeleteOnSubmit(entity);
  }

  /// <summary>
  /// Create a new instance of type T.
  /// </summary>
  /// <returns></returns>
  public virtual T New()
  {
      T entity = Activator.CreateInstance<T>();
      GetTable.InsertOnSubmit(entity);
      return entity;
  }

  /// <summary>
  /// Adds an insance T.
  /// </summary>
  /// <returns></returns>
  public virtual void Insert(T entity)
  {
      GetTable.InsertOnSubmit(entity);
  }

  /// <summary>
  /// Update entity.
  /// </summary>
  /// <returns></returns>
  public virtual void Update(T entity)
  {
      DC.Context.Refresh(System.Data.Linq.RefreshMode.KeepCurrentValues, entity);
  }

  /// <summary>See IRepository</summary>
  public void SubmitChanges()
  {
      DC.SubmitChanges();
  }

  private string PrimaryKeyName
  {
      get { return TableMetadata.RowType.IdentityMembers[0].Name; }
  }

  private System.Data.Linq.Table<T> GetTable
  {
      get { return DC.Context.GetTable<T>(); }
  }

  private System.Data.Linq.Mapping.MetaTable TableMetadata
  {
      get { return DC.Context.Mapping.GetTable(typeof(T)); }
  }

  private System.Data.Linq.Mapping.MetaType ClassMetadata
  {
      get { return DC.Context.Mapping.GetMetaType(typeof(T)); }
  }
}

Answer 1

Is it because you are calling .InsertOnSubmit(entity) twice?

You call it once in New()

public virtual T New()
{
    T entity = Activator.CreateInstance<T>();
    GetTable.InsertOnSubmit(entity);
    return entity;
}

And then again in .Insert()

public virtual void Insert(T entity)
{
    GetTable.InsertOnSubmit(entity);
}

Personally I would remove the GetTable.InsertOnSubmit(entity) from the New() method.

Reason being that I think it would be better for the user of the repository to specifically insert the entity rather than it automatically get set for insertion every single time they create a new one.

HTHs,
Charles