ASP.NET MVC2, LINQ-TO-SQL relationship entities, select list, model binding

Say you have the following scenario:

• Table: Country; Columns: CountryID, CountryName
• Table: State; Columns: StateID, StateName, CountryID (foreign key)
• Table: Locality; Columns: LocalityID, LocalityName, StateID (f开发者_开发知识库oreign key)

In MVC, it is nice that the auto-generated LINQ-TO-SQL classes map association relationships in the code so you can call the linked foreign entity, e.g. in my view I can have:

<% foreach (var locality in Model.Localities) { %>

    <tr>
        <td>
            <%: locality.LocalityName %>
        </td>
        <td>
            <%: locality.State.StateName %>
        </td>
        <td>
            <%: locality.State.Country.CountryName %>
        </td>
    </tr>

<% } %>

This succesfully renders when I browse to the index action.

However, I am having problems with the Edit action. Here's the code:

        <strong>Locality Name</strong>
        <div class="editor-field">
            <%: Html.TextBox("LocalityName", Model.Locality.LocalityName) %>
            <%: Html.ValidationMessage("LocalityName")%>
        </div>

        <strong>Country</strong>
        <div class="editor-field">
            <%= Html.DropDownList("CountryID", Model.CountriesDDL, "-- select --") %>
        </div>

        <strong>State</strong>
        <div class="editor-field">
            <%= Html.DropDownList("StateID", Model.StatesDDL, "-- select--") %>
            <%: Html.ValidationMessage("StateID")%>
        </div>

At first I was getting a validation error next to the selectlist of states (for the StateID) which said, e.g., "8 is not a valid value." So it isn't updating.

I understand, from reading a number of posts (such as this one), that there is a database-related problem updating the relationship by setting the ID, and that the solution appears to be to set the ENTITY instead. (Incidentally, contrary advice is also dispensed here). Following this advice, I have been looking at overloads of Html.DropDownList() to set the "value" of the list item to the object itself, whilst setting the "text" property to the Object.Name - I haven't solved this yet. But as this undertaking is becoming more time-consuming, I would very much appreciate some expert advice.

Therefore, my questions are: will this actually work if I get it going? And is it possible to get the SelectList to work this way (and any suggestions as to how)?

Thanks for your time,

Tim.

In general it is also not a good idea to pass your domain model to your View (except perhaps in list Views).

Better using a (proxy) ViewModel which is a flattened version of your domain model. It is a bit more work, but works like a charm.

Try playing with this code to populate your list, it works for me., here I am working with product.

           <%:Html.DropDownListFor(m => m.Id, new SelectList(Model.Categories, "Id", "Name", Model.Product.CategoryId, "-Select-")%>

Use DTOs for showing list like stuff. Entities can be used for Create,Update,Delete