CODEWITHSUNDEEP
asp.netlinqjoin
HereToLearn
HereToLearn

Reputation: 282

Complex LINQ Queries (Multiple Joins)

I'm fairly new to LINQ and I am having a bit of trouble with my query. I am trying to fetch surveys that are associated to particular groups (SurveyGroups table is the assignment table). However, once I return my model to my View I get a null error.

This is what I have so far:

public ActionResult Index()
    {
        var userID = User.Identity.GetUserId();
        var clientID = _db.Users.Where(u => u.Id == userID).Select(u => u.ClientID).FirstOrDefault();
        var userGroups = _db.UserGroups.Where(x => x.UserID == userID).ToList();

        var groupedSurveys = (from t1 in userGroups
                              join t2 in _db.SurveyGroups
                    on t1.GroupID equals t2.GroupID
                    select new { t2.SurveyID }).ToList();

        var surveys = (from t11 in groupedSurveys
                       join t22 in _db.Surveys.Where(s => s.ClientID == clientID)
                       on t11.SurveyID equals t22.SurveyID
                       select new { t22.ClientID, t22.Name}).ToList();

        return View("~/Views/User/Dashboard.cshtml", surveys);
    }
  1. Firstly, I get the userID.
  2. I get the ClientID associated with that userID.
  3. Then I join userGroups object with the SurveyGroup table.
  4. Lastly, I join groupedSurveys with the Surveys table.

Any guidance would be greatly appreciated!

UPDATED:

The error I am receving is the following:

The model item passed into the dictionary is of type 'System.Collections.Generic.List1[<>f__AnonymousType65[System.Int32,System.Nullable1[System.Int32],System.Nullable1[System.Int32],System.Nullable1[System.Int32],System.String]]', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable1[SM_XPRESS.Models.Survey]'.

Upvotes: 1

Views: 90

Answers (1)

John Wu
John Wu

Reputation: 52290

In this line:

select new { t22.ClientID, t22.Name}

...you are creating a new instance of an anonymous type, based on the data in t22 (which is a survey record).

However, the list you need to provide to your view needs to be a list of Survey instances, not a list of anonymous type instances.

So change it to

select t22

and you're good to go.

Upvotes: 2

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