[Solved] An expression of type XXXX is not allowed in a subsequent from clause in a query expression with source type 'System.Linq.IQueryable<XXXX>'. Type inference failed in the call to 'SelectMany'

[Duncan]

I am getting the following error:

An expression of type XXXX is not allowed in a subsequent from clause in a query expression with source type 'System.Linq.IQueryable<XXXX>'.  Type inference failed in the call to 'SelectMany'

I am extremely new to LINQ. I have been using SQL queries with the Open Access SQL API which has been working great. But I want to learn to use LINQ so I a researching and forcing myself to do this.

I found the following articles which describes how LINQ handles relationships between tables. This is where I was struggling the most and this article does a great job of explaining it. http://msdn.microsoft.com/en-us/library/bb386932.aspx
So I am trying to duplicate this, but using OpenAccess ORM.

So this is my query:

var idQuery = from u in dbContext.Users
              from c in u.UserGroups
              where u.CredentialsID == 0
              select new
              {
                  u.UserID,
                  u.FirstName,
                  u.MiddleName,
                  u.LastName,
                  u.Gender,
                  u.Birthday,
                  u.CreatedOn
              };

u.UserGroups is throwing the error. Intelisense shows me the UserGroups object but doesn’t like something I am doing… Would someone be able to help me identifying what is causing this error please…

Thanks in advance.

Duncan

[Ady]

Hello Duncan,

It seems that like u.UserGroups is a single object and the from clause expects a sequence of objects. Is u.UserGroups a queryable type that implements IEnuerable or IEnumerable<T>? You can find additional informatio here.
Alternatively you could modify your query to the following at it would work but I am not sure that is the result you expect

var idQuery = from u in dbContext.Users
              let c = u.UserGroups
              where u.CredentialsID == 0
              select new
              {
                  u.UserID,
                  u.FirstName,
                  u.MiddleName,
                  u.LastName,
                  u.Gender,
                  u.Birthday,
                  u.CreatedOn
              };

Do get back in case you need further assistance


Regards,
Ady
the Telerik team