LINQ Distinct()

Question

I am working on getting the results of this sql query in LINQ

SELECT DISTINCT(Type)
FROM  Product
WHERE categoryID = @catID

this is my repository query:

public IQueryable<ProdInfo> GetProdInfo()
        {

            var data = from u in db.Prod
                       select new ProdInfo
                       {
                           PID = u.PID,
                           CatID = u.CatID,                           
                           LastChanged = u.LastChanged,
                           ChangedBy = u.ChangedBy,                               
                           Type = u.Type,
                       };

            return data;
        }

filter:

public static IQueryable<ProdInfo> GetDistinctProdType(this IQueryable<ProdInfo> qry,int CatID)
            {
                return from p in qry
                       where p.CatID.Equals(CatID)
                       select p;
            }

I need the filter to return the distinct prod type? How can i do this?

Answer 1

return (from p in qry
       where p.CatId.Equals(CatID)
       select p.Type).Distinct();

This matches what your provided SQL Query should be doing.

Answer 2

Simply like this:

public static IQueryable<ProdType> GetDistinctProdType(
    this IQueryable<ProdInfo> query,
    int categoryId)
{
    return (from p in query
            where p.CatID == categoryId
            select p.Type).Distinct();
}

Note that I've changed the return type - it should match whatever the type of ProdInfo.Type is.

You may find it more readable to use the extension methods for the whole query if the query expression itself is reasonably simple:

public static IQueryable<ProdType> GetDistinctProdType(
    this IQueryable<ProdInfo> query,
    int categoryId)
{
    return query.Where(p => p.CatID == categoryId)
                .Select(p => p.Type)
                .Distinct();
}