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POMVC dbContext find parent record when current record has no elements
 

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  1. POMVC dbContext find parent record when current record has no elements
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    <p>I'm a MVC/C# beginner so go easy.</p> <p>I have an existing database where a Customer has zero or many Projects. I've built an ASP.Net project from ADODB Entity data model and dbContext code generators.</p> <p>I have a customer: Joe Bloggs (ID=7). I click on the 'Projects' link for Joe Bloggs in my form to see his projects. He doesn't have any. I want to create a project for him so I call the Create action on the project controller.</p> <p>I need to pass Joe Bloggs ID to the Create action for three reasons (which may not be necessary - please enlighten me if need be)</p> <ol> <li><p>Because this is a project for Joe Bloggs I need to pass ID=7 into the controller so I can set the default Customer ID for him when generating the model data for the create view</p></li> <li><p>When I hit the Cancel button on the Create view, I want to go back to the originally filtered view of projects based on Joe Blogs</p></li> <li><p>When I hit save I want to got back to the originally filtered view of projects based on Joe Bloggs.</p></li> </ol> <p>Anyway if I <em>do</em> have one or more projects for Joe Bloggs then I can use this monster below to access his id from the model data within the view:</p> <pre><code>&lt;input type="button" title = "New Project" value="New Project" onclick="location.href='@Url.Action("Create", new { id = Model.First().Customer_ID })'" /&gt; </code></pre> <p>Here is the issue: if he doesn't have any projects, Model.First() doesn't return anything so I can't find the 'parent' Customer_ID record.</p> <p>I used dbContext to generate the model classes (this is a data-first development). Something tells me I could extend these classes or create a new class to allow for the case above.</p> <p>My current workaround is to use ViewBag to pass the various id's and strings from viewer > controller like a hot potato but this means if get three deep (Customer > Proejct > Task), and I want to display the customer name on the task, I've passed it twice. It smells.</p> <p>I notice that the drop down in the Project Index view <strong>has the Customer in it</strong>. Here is my code for that:</p> <pre><code>@Html.DropDownList("Customer_ID", null, "Select a Customer to Filter", new { @onchange = "this.form.submit();" }) </code></pre> <p>I might be able to hack it out of there but really I want to be able to traverse up from a class which might be two or three deep and far removed from this drop down</p> <p>Here is an abridged Customer and CustomerProject class generated from dbContext</p> <pre><code>public partial class Customer { public Customer() { this.Tasks = new HashSet&lt;Task&gt;(); this.CustomerProjects = new HashSet&lt;CustomerProject&gt;(); } public int Customer_ID { get; set; } public string Customer_Name { get; set; } public virtual ICollection&lt;CustomerProject&gt; CustomerProjects { get; set; } } public partial class CustomerProject { public CustomerProject() { this.Tasks = new HashSet&lt;Task&gt;(); this.CustomerProjectTasks = new HashSet&lt;CustomerProjectTask&gt;(); } public int CustomerProject_ID { get; set; } public int Customer_ID { get; set; } public string Project_Name { get; set; } public virtual ICollection&lt;Task&gt; Tasks { get; set; } public virtual Customer Customer { get; set; } public virtual ICollection&lt;CustomerProjectTask&gt; CustomerProjectTasks { get; set; } } </code></pre> <p>I'm sure there is an obvious solution but my strength is in databases and VB6, not C#</p> <p>At Mystere Man's suggestion I have built a ViewModel class, but I'm having a little trouble:</p> <p>Here is what's in my model class file (as I understand it this is just a wrapper around the the existing project entity):</p> <pre><code>namespace zzz.Models { using System; using System.Collections.Generic; public class ProjectsViewModel { public int Customer_ID { get; set; } public ICollection&lt;CustomerProject&gt; CustomerProjects; } } </code></pre> <p>Here's whats in the Index action of my controller (I havejust added my existing Project collection to the new ViewModel class):</p> <pre><code> public ViewResult Index(int pCustomer_ID = 0, string pProjectName_Filter = "") { // Set up drop down ViewBag.Customer_ID = new SelectList(db.Customers.OrderBy(x =&gt; x.Customer_Name), "Customer_ID", "Customer_Name"); //ViewBag.Selected_Customer_ID = Customer_ID; // If no parameters entered, show nothing // Otherwise optionally filter each parameter var projects = from p in db.CustomerProjects orderby p.Active, p.Project_Order where (p.Project_Name.Contains(pProjectName_Filter) || pProjectName_Filter.Equals("")) &amp;&amp; (p.Customer_ID == pCustomer_ID || pCustomer_ID.Equals(0)) &amp;&amp; !(pCustomer_ID.Equals(0) &amp;&amp; pProjectName_Filter.Equals("")) select p; var customerprojects = new ProjectsViewModel { Customer_ID = pCustomer_ID, CustomerProjects = projects.ToList() }; return View(customerprojects); } </code></pre> <p>Here's an extract from my view (I have tried to iterate through the Project collection within the ViewModel class):</p> <pre><code>@model IEnumerable&lt;BistechPortal.Models.ProjectsViewModel&gt; &lt;table&gt; @foreach (var item in Model.CustomerProjects) { &lt;tr&gt; &lt;td&gt; @Html.DisplayFor(modelItem =&gt; item.Project_Name) &lt;/td&gt; &lt;/tr&gt; } &lt;/table&gt; </code></pre> <p>When I run the Index action, on the foreach line I get:</p> <pre><code>'System.Collections.Generic.IEnumerable&lt;zzzzPortal.Models.ProjectsViewModel&gt;' does not contain a definition for 'CustomerProjects' " </code></pre> <p>Please translate - why can't it find my 'CustomerProjects' collection inside my ViewModel?</p>
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    1. COAs I understand, your Model is of type `Customer`, so you want to have `<input type="button" title = "New Project" value="New Project" onclick="location.href='@Url.Action("Create", new { id = Model.Customer_ID })'" />`
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