how to assign value to entity got from database - asp.net

Question

I have a linq query like below:
public IQueryable<vmEmp> GetEmp(int crewid)
{
var dt = new EmpEntities();
var e = from t in dt.tblEmp
where (t.CrewId == crewid)
select new vmEmp
{
Id = -1,
Crew = t.crewid,
Name = t.Name,
Address = t.Address
};
return e;
}
I hope can make the Id auto decrease by 1 till end of the employee.
like first's Id is -1, second's is -2, third is -3 ...
How to do that here? Thanks a lot

Answer 1

If this was LINQ-to-objects, you could use this overload of Select:
var dt = new EmpEntities();
var e = dt.tblEmp
.Where(t => t.CrewId == crewid)
.Select((t,index) => new vmEmp
{
Id = -index - 1,
Crew = t.crewid,
Name = t.Name,
Address = t.Address
});
But EF doesn't suport this, because the indexer can't be translated into SQL. So you need a work-around:
var dt = new EmpEntities();
var e = dt.tblEmp
.Where(t => t.CrewId == crewid)
.Select(t => new
{
Id = 0,
Crew = t.crewid,
Name = t.Name,
Address = t.Address
}
.AsEnumerable() // Continue in memory
.Select((t,index) => new vmEmp
{
Id = -index - 1,
Crew = t.Crew,
Name = t.Name,
Address = t.Address
});
Side note: it's recommended to put dt in a using construct.

Answer 2

Use a counter variable and decrease it for every record while you project it to your custom POCO.
public IQueryable<vmEmp> GetEmp(int crewid)
{
int counter=0;
var dt = new EmpEntities();
//load the items to a list of anonymous type
var eList = from t in dt.tblEmp
where (t.CrewId == crewid)
.Select(s=>
new { Id = 0,
Crew = s.crewid,
Name = s.Name,
Address = s.Address
}).ToList();
var e=eList.Select(x=> new vmEmp
{
Id = --counter,
Crew = x.Crew,
Name = x.Name,
Address = x.Address
});
return e.AsQueryable();
}