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• SQL Subquery in LINQ for Entity Framework 4.0

  - by Jorin

  I'm new to LINQ and EF, but I've been able to stumble through for the majority of the queries I have, but this one has me completely confused. No matter what I try, it comes up in SQL Profiler as a big mess :-). I have two tables: Users and UsersProjects. The goal of this query is to list all the users who are working on projects with the specified user. Here is the query as I have it written in SQL. It's a subquery, but I don't know of a way to simplify it further, but I'm open to suggestions there as well. SELECT DISTINCT Users.FirstName, Users.LastName FROM Users INNER JOIN UsersProjects ON Users.ID=UsersProjects.UserID WHERE UsersProjects.ProjectID IN (SELECT ProjectID FROM UsersProjects WHERE UserID=@UserID) Anybody able to help?? It seems like a fairly simple subquery in SQL, but in LINQ, I'm baffled. Thanks, Jorin

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• ASP.NET MVC Concurrency with RowVersion in Edit Action

  - by Jorin

  I'm wanting to do a simple edit form for our Issue Tracking app. For simplicity, the HttpGet Edit action looks something like this: // Issues/Edit/12 public ActionResult Edit(int id) { var thisIssue = edmx.Issues.First(i => i.IssueID == id); return View(thisIssue); } and then the HttpPost action looks something like this: [HttpPost] public ActionResult Edit(int id, FormCollection form) { // this is the dumb part where I grab the object before I update it. // concurrency is sidestepped here. var thisIssue = edmx.Issues.Single(c => c.IssueID == id); TryUpdateModel(thisIssue); if (ModelState.IsValid) { edmx.SaveChanges(); TempData["message"] = string.Format("Issue #{0} successfully modified.", id); return RedirectToAction("Index"); } return View(thisIssue); } Which works wonderfully. However, the concurrency check doesn't work because in the Post, I'm re-retreiving the current entity right before I attempt to update it. However, with EF, I don't know how to use the fanciness of SaveChanges() but attach my thisIssue to the context. I tried to call edmx.Issues.Attach(thisIssue) but I get The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state. How do I handle concurrency in MVC with EF and/or how do I properly Attach my edited object to the context? Thanks in advance

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• Entity Framework Update Entity along with child entities (add/update as necessary)

  - by Jorin

  I have a many-to-many relationship between Issues and Scopes in my EF Context. In ASP.NET MVC, I bring up an Edit form that allows the user to edit a particular Issue. At the bottom of the form, is a list of checkboxes that allow them to select which scopes apply to this issue. When editing an issue, it likely will always have some Scopes associated with it already--these boxes will be checked already. However, the user has the opportunity to check more scopes or remove some of the currently checked scopes. My code looked something like this to save just the Issue: using (var edmx = new MayflyEntities()) { Issue issue = new Issue { IssueID = id, TSColumn = formIssue.TSColumn }; edmx.Issues.Attach(issue); UpdateModel(issue); if (ModelState.IsValid) { //if (edmx.SaveChanges() != 1) throw new Exception("Unknown error. Please try again."); edmx.SaveChanges(); TempData["message"] = string.Format("Issue #{0} successfully modified.", id); } } So, when I try to add in the logic to save the associated scopes, I tried several things, but ultimately, this is what made the most sense to me: using (var edmx = new MayflyEntities()) { Issue issue = new Issue { IssueID = id, TSColumn = formIssue.TSColumn }; edmx.Issues.Attach(issue); UpdateModel(issue); foreach (int scopeID in formIssue.ScopeIDs) { var thisScope = new Scope { ID = scopeID }; edmx.Scopes.Attach(thisScope); thisScope.ProjectID = formIssue.ProjectID; if (issue.Scopes.Contains(thisScope)) { issue.Scopes.Attach(thisScope); //the scope already exists } else { issue.Scopes.Add(thisScope); // the scope needs to be added } } if (ModelState.IsValid) { //if (edmx.SaveChanges() != 1) throw new Exception("Unknown error. Please try again."); edmx.SaveChanges(); TempData["message"] = string.Format("Issue #{0} successfully modified.", id); } } But, unfortunately, that just throws the following exception: An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key. What am I doing wrong?

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• Entity Framework - Many to Many Subquery

  - by Jorin

  I asked a question about this previously but my database structure has changed, and while it made other things simpler, now this part is more complicated. Here is the previous question. At the time, my EF Context had a UsersProjects object because there were other properties. Now that I've simplified that table, it is just the keys, so all my EF context knows about is Users and Projects and the M2M relationship between them. There is no more UsersProjects as far as EF knows. So my goal is to say "show me all the users who are working on projects with me." in SQL, this would go something like: SELECT * FROM Users INNER JOIN UsersProjects ON Users.ID=UsersProjects.UserID WHERE ProjectID IN (SELECT ProjectID FROM UsersProjects WHERE UserID=@UserID) and I started in EF with something like this: var myProjects = (from p in edmx.Projects where p.Users.Contains(edmx.Users.FirstOrDefault(u => u.Email == UserEmail)) orderby p.Name select p).ToList(); var associatedUsers = (from u in edmx.Users where myProjects.Contains(?????????) //where myProjects.Any(????????) select u); The trick is finding what to put in the ????????. Anyone help here?

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