Question

Linq to Sql union with constant values

Asked by: GordonLiq

Hi ,
how to union the return value with constant ?

my code comes the error says the union type incompitable.

I have to union them on linq becase this is used for a lookup control.

var staffs=from rs in DBLinq.tblFacilityStaffs                                 
                                  select new { OptName = string.Format("{0} {1}", rs.FirstName, rs.LastName), rs.UNID };
var extrastaff=(from rs in DBLinq.tblFacilityStaffs
                            select new { OptName = "", UNID = 0 }).Take(1);
            bsstaff.DataSource = staffs.Union(extrastaff);

                                  
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Asked On
2009-10-27 at 16:20:22ID24849255
Topics

Language Integrated Query - LINQ

,

C# Programming Language

Participating Experts
1
Points
500
Comments
5

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Answers

 

by: TheLearnedOnePosted on 2009-10-28 at 06:19:31ID: 25682896

That sounds like you are trying to union between two different anonymous types, and it might explain the error.  Did you try a single LINQ query statement instead?

 

by: GordonLiqPosted on 2009-10-28 at 13:47:02ID: 25688158

how to do that?

 

by: TheLearnedOnePosted on 2009-10-28 at 15:01:03ID: 25688793

I researched this question in more detail, and I discovered what you really meant.

I created this example, and looked at the generated queries from AdventureWorks data:

            var q1 = from employee in dc.vEmployees
                    select new { First = employee.FirstName, Last = employee.LastName };

            var q2 = from employee in dc.vEmployees
                     select new { First = "(Blank)", Last = "(Blank)"};

q1
----
{SELECT [t0].[FirstName] AS [First], [t0].[LastName] AS [Last]
FROM [HumanResources].[vEmployee] AS [t0]
}

q2
----
SELECT NULL AS [EMPTY]
FROM [HumanResources].[vEmployee] AS [t0]
}

This appears to be a bug, since it doesn't generate the same queries, which make the Union incompatible.

I am looking into a work-around.

 

by: TheLearnedOnePosted on 2009-10-28 at 15:05:54ID: 25688827

I believe what you need to use is the AsEnumerable method, as in this example:

            AdventureWorksData dc = new AdventureWorksData();
 
            var q1 = from employee in dc.vEmployees
                    select new { First = employee.FirstName, Last = employee.LastName };
 
            var q2 = from employee in dc.vEmployees
                     select new { First = "(Blank)", Last = "(Blank)"};
 
            var result = q2.AsEnumerable().Union(q1);
 
            foreach (var r in result)
            {
                Console.WriteLine(r.First + " " + r.Last);
            }
                                              
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by: GordonLiqPosted on 2009-10-29 at 01:39:28ID: 31646735

Thanks , that is wonderful.

20120131-EE-VQP-002

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