MVC 4. and Entity Framework Table Join

Question

This item is driving me mad ;-) I am trying to do a simple query joining two tables

I have the following:

Repository Class method

 public IQueryable<ADPerson> FindAll(string UserId)
    {
        return (from p in db.ADPerson
                select p); 


    }

In my Controller:

  var ADPersonList = from o in ADPersonDB.FindAll(GetUserId())
                    join c in MSDNTypeDB.FindAll(GetUserId()) on o.MsdnTypeId equals c.MsdnTypeId
                    select new ADPerson()
                    {

                        AdPersonId = o.AdPersonId,
                        SamAccountName = o.SamAccountName,
                        Description = o.Description,
                        DisplayName = o.DisplayName,
                        UserPrincipalName = o.UserPrincipalName,
                        Enabled = o.Enabled,
                        LastUpdated = o.LastUpdated,
                        OnlineAssetTag = o.OnlineAssetTag,
                        MsdnTypeId = o.MsdnTypeId,
                        MsdnSubscription = c.MsdnTypeDescription,


                    };

I keep getting an error:

{"The specified LINQ expression contains references to queries that are associated with different contexts."}

I also tried adding to the repository class:

Repository Class method

 public IQueryable<ADPerson> FindAll(string UserId)
    {
        //return (from p in db.ADPerson
        //        select p); 

        var query = from o in db.ADPerson
                    join c in db.MsdnTypes on o.MsdnTypeId equals c.MsdnTypeId
                    select new ADPerson()
                    {

                        AdPersonId = o.AdPersonId,
                        SamAccountName = o.SamAccountName,
                        Description = o.Description,
                        DisplayName = o.DisplayName,
                        UserPrincipalName = o.UserPrincipalName,
                        Enabled = o.Enabled,
                        LastUpdated = o.LastUpdated,
                        OnlineAssetTag = o.OnlineAssetTag,
                        MsdnTypeId = o.MsdnTypeId,

                        MsdnSubscription = c.MsdnTypeDescription,


                    };

        return query;

    }

is it really so hard to do a simple join between two tables and populate the variable in Entity framework

Thanks

Solution 1

Project to an anonymous object

var query = from o in db.ADPerson
   join c in db.MsdnTypes on o.MsdnTypeId equals c.MsdnTypeId
   select new 
   {
     AdPersonId        = o.AdPersonId,
     SamAccountName    = o.SamAccountName,
     Description       = o.Description,
     DisplayName       = o.DisplayName,
     UserPrincipalName = o.UserPrincipalName,
     Enabled           = o.Enabled,
     LastUpdated       = o.LastUpdated,
     OnlineAssetTag    = o.OnlineAssetTag,
     MsdnTypeId        = o.MsdnTypeId,
     MsdnSubscription  = c.MsdnTypeDescription,
  };

Then map back to your entity

foreach (var item in query)
{
  var adPerson = new ADPerson
  {
    AdPersonId         = item.AdPersonId,
    SamAccountName     = item.SamAccountName,
    Description        = item.Description,
    DisplayName        = item.DisplayName,
    UserPrincipalName  = item.UserPrincipalName,
    Enabled            = item.Enabled,
    LastUpdated        = item.LastUpdated,
    OnlineAssetTag     = item.OnlineAssetTag,
    MsdnTypeId         = item.MsdnTypeId,
    MsdnSubscription   = item.MsdnTypeDescription,
  {
}

Solution 2

   public IQueryable<ADPerson> FindAll(string UserId)
    {
       // return (from p in db.ADPerson
       //        select p);
        List<ADPerson> lst = new List<ADPerson>();
        var query = from o in db.ADPerson
                    join c in db.MsdnTypes on o.MsdnTypeId equals c.MsdnTypeId
                    select new
                         {

                             AdPersonId = o.AdPersonId,
                             SamAccountName = o.SamAccountName,
                             Description = o.Description,
                             DisplayName = o.DisplayName,
                             UserPrincipalName = o.UserPrincipalName,
                             Enabled = o.Enabled,
                             LastUpdated = o.LastUpdated,
                             OnlineAssetTag = o.OnlineAssetTag,
                             MsdnTypeId = o.MsdnTypeId,
                             MsdnSubscription = c.MsdnTypeDescription

                         };
        foreach (var item in query)
        {
            var adPerson = new ADPerson()
              {
                  AdPersonId = item.AdPersonId,
                  SamAccountName = item.SamAccountName,
                  Description = item.Description,
                  DisplayName = item.DisplayName,
                  UserPrincipalName = item.UserPrincipalName,
                  Enabled = item.Enabled,
                  LastUpdated = item.LastUpdated,
                  OnlineAssetTag = item.OnlineAssetTag,
                  MsdnTypeId = item.MsdnTypeId,
                  MsdnSubscription = item.MsdnSubscription
              };
            lst.Add(adPerson);

        }

        return lst.AsQueryable();



    }

Comments

[mattytommo]

Is it the same error using the second method?

[David Costelloe]

Excellent point: No the error returned on the second is: The entity or complex type 'project.Models.ADPerson' cannot be constructed in a LINQ to Entities query.

[Forty-Two]

RE: the second error. That's because you cannot project onto a mapped entity. You may project the query to an anonymous object, and then map it to the ADPerson entity afterwards

[Forty-Two]

Alternatively, you may choose to create an un-mapped DTO, project to that, then map back to the ADPerson entity.

[David Costelloe]

Oh so return as List rather than IQuerable? Sorry little confused as both tables are mapped in repository classes..ok not sure how to create an un-mapped DTO and map back again

[David Costelloe]

The first var query is failing is there suppose to be select new?

[Forty-Two]

@DavidCostelloe yes, sorry. Edited answer

[eburgos]

it might be you have a trailing comma at "MsdnSubscription = c.MsdnTypeDescription," and also on the second one

[David Costelloe]

Thanks found it was the brace { and }; almost there :-)

[David Costelloe]

getting error "Invalid column name 'MsdnSubscription" on display of field

[David Costelloe]

I should be returning query but it says I can't due to being anonymous.

[David Costelloe]

Looks like I need to convert the anonymous to Iquerable<ADPerson> any ideas on how i can do that. Does seem like an aweful lot of trouble to join a table in the Entity framework there must be an easier way?

[Forty-Two]

@david that's what the for each loop does. It converts each anonymous object returned by the query to an ADPerson entity. Just declare a new list of ADPerson and add each entity to the list as it is converted.

[David Costelloe]

thanks once you mentioned that it became obvious on what was needed. Finally works the way it should. Updated as answered and complete. I spend way to much trying to come up with a complex way when I should have been looking to the simple way :-(