Question

I want to SELECT all the data from a particular table by adding a countField to the results that counts the number of times that the corresponding Item.ResourceId exists in all the results.

SELECT Name, ResourceId, (SELECT COUNT(ResourceId) FROM Item GROUP BY ResourceId) AS foo
FROM Item

Any ideas on how to do this?

Answer 1

If this is your desired query

SELECT Name, ResourceId, COUNT(*) FROM Item GROUP BY Name, ResourceId;

it translates to LINQ as follows.

var result = items.GroupBy(item => new { item.Name, item.ResourceId })
                  .Select(group => new { group.Key.Name, group.Key.ResourceId, Count = group.Count() })
                  .ToList();

Or do you want this query?

SELECT Name,
       ResourceId,
       (SELECT COUNT(*) FROM Item y WHERE y.ResourceId = x.ResourceId)
FROM
       Item x;

This translates to the following LINQ expression.

var result = items.Select(item => new
             {
                 item.Name,
                 item.ResourceId,
                 Count = items.Count(x => x.ResourceId == item.ResourceId)
             }).ToList();

Given the following input

Name   ResourceId
-----------------
 A      1
 A      1
 B      1
 B      2
 B      2
 C      3

the first query yields

Name   ResourceId   Count
-------------------------
 A      1            2
 B      1            1
 B      2            2
 C      3            1

while the second query yields this.

Name   ResourceId   Count
-------------------------
 A      1            3
 A      1            3
 B      1            3
 B      2            2
 B      2            2
 C      3            1