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POEF: Update entity stored in session
 

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  1. POEF: Update entity stored in session
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    <p>I'm using EF 5 with Web Forms (ASP.NET 4.5), with the "one DbContext instance per request" approach. </p> <p>But this situation is a bit complicated: I have a multi-step create/edit screen, and I store the current entity in Session, then I manipulate it and in the final step, I commit it to the Database.</p> <p>Creating a new instance was fine, but I can't for the life of me edit an existing entity... Because it's another request, my original DbContext instance was lost and when I attach it to a new one, I get the <strong>An entity object cannot be referenced by multiple instances of IEntityChangeTracker</strong> error.</p> <p>My code is far too complex to post here, but I'll try and summarize it accurately:</p> <p>My DbContext:</p> <pre class="lang-cs prettyprint-override"><code>public class AppContext : DbContext { // DbSet declarations... public static AppContext Current { get { var context = HttpContext.Current.Items["Contexts.AppContext"] as AppContext; if (context == null) { context = new AppContext(); HttpContext.Current.Items["Contexts.AppContext"] = context; } return context; } } } </code></pre> <p>An example of what the page code looks like:</p> <pre class="lang-cs prettyprint-override"><code>protected void Page_Load(object sender, EventArgs e) { int? id = null; // After this, I try to get it from the QueryString, parse it, etc.. Omitted for sake of brevity // If I have an ID, it means I'm editing... Session["Product"] = id.HasValue ? new Product() : AppContext.Current.Products.Find(id)); MethodToPopulateFields(); // Internally, it uses the Session variable } protected void Step1(){ // through n // Manipulates the Session["Product"] based on page input... } protected void Save(){ var product = Session["Product"] as Product; if(product.ID == 0) product = AppContext.Current.Products.Add(product); // throws an exception: // AppContext.Current.Entry(product).State = EntityState.Modified; // this too: // AppContext.Products.Attach(product); AppContext.Current.SaveChanges(); } </code></pre> <p>I know I can get the old entity from the database, update it manually and save, all in the last step, but I really don't want to do that...</p> <p>Thank you.</p>
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    1. USRafael Soares
    1. USRafael Soares
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    1. COFYI, using session for this is a terrible approach. A better solution is to serialize your individual steps to each successive step using something like @Html.Serialize from the MvcFutures project. This way you don't have to worry about concurrency issues (like if a user has two versions of the form open in two different tabs of the browser). It also means that if the user gets up for a bathroom break, they don't have to worry about the session being gone when they get back.
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      1. POEF: Update entity stored in session
      1. USErik Funkenbusch
    2. COI see your point, but it is a Web Forms app, not MVC. Also, it's a legacy app (which I just upgraded to ASP.NET 4.5)... Kinda hard to change it at this point.
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      1. POEF: Update entity stored in session
      1. USRafael Soares
    3. COIn that case, you have an even better option, which is the Asp.net PreviousPage property, which gives you access to the previous pages data. This is what it's designed for.
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      1. POEF: Update entity stored in session
      1. USErik Funkenbusch
 

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