Linq query with multiple subqueries

Question

I'm working on converting an Oracle Sql query to Linq, and not sure how to proceed. Here is the Sql query:

SELECT *
FROM   CustomerShip,
    (SELECT DISTINCT b.ShipSeq AS shipSeq
     FROM   Orders a,
            CustomerShip b
     WHERE  a.OrderId IN (SELECT OrderId
                          FROM   Orders
                          WHERE  CustomerId = @CustomerId
                          AND    OrderType <> 'A')
     AND    b.CustomerId = @CustomerId
     AND    b.ShipSeq = a.CustShip
     AND    OrderStatus <> 'C'
     GROUP BY b.ShipSeq) i
WHERE  CustomerId = @CustomerId
AND    (Address NOT LIKE '%RETAIL%STORE%')
AND    ShipSeq = i.ShipSeq(+)
ORDER BY ShipTo DESC, OrderDate DESC;

I have tried to break it down into three separate queries when converting to linq.

var query1 = from c in CustomerShip
            where c.CustomerId == customerId
            && !c.Address.Contains("RETAIL")
            && !c.Address.Contains("STORE")
            orderby c.ShipTo descending, c.OrderDate descending
            select c;

var query2 = from o in Orders
         where o.CustomerId == customerId
         && !o.OrderType.Equals("A")
         select o.OrderId;

var query3 = (from o in Orders
         from c in CustomerShip
         where c.CustomerId == customerId
         && c.ShipSeq == o.CustShip
         && !o.OrderStatus.Equals("A")
         select c.ShipSeq).Distinct();

Now I'm trying to assemble them all into one query, but unsure how to do it. Here is the direction I am going:

var query = from c in CustomerShip

let subquery = from o in Orders
               where o.CustomerId == customerId
               && !o.OrderType.Equals("A")
               select o.OrderId

    from or in model.Orders
    where subquery.Contains(or.OrderId) 
    && c.CustomerId == customerId
    && c.ShipSeq == or.CustShip
    && !or.OrderStatus.Equals("A")
    group c by c.ShipSeq
    into i
    select c.ShipSeq

where c.CustomerId == customerId
&& !c.Address.Contains("RETAIL")
&& !c.Address.Contains("STORE")
orderby c.ShipTo descending, c.OrderDate descending 
select c, i;

UPDATE

I have a query that kinds works, but the it takes almost two minutes to execute (compared to .02s for the Oracle query) and the order of the results is incorrect. Anyone see what I'm missing?

var innerQuery = from x in model.Orders
                    where x.CustomerId == customerId
                    && !x.OrderType.Equals("A")
                    select x.OrderId;

var result = from c in model.CustomerShip
            join subQuery in 
            (
                (from o in model.Orders
                from c in model.CustomerShip 
                where c.CustomerId == customerId
                && innerQuery.Contains(o.OrderId)
                && !o.FLAG_ORD_STATUS.Equals("C")
                && c.ShipSeq == o.CustShip
                select c.ShipSeq).Distinct()

            ) on c.ShipSeq equals subQuery into temp
            from x in temp.DefaultIfEmpty()
            where c.CustomerId == customerId
            && !c.Address.Contains("RETAIL")
            && !c.Address.Contains("STORE")
            orderby c.ShipTo descending, c.OrderDate descending
            select c;

Answer 1

Remember that you are just build a query here. Nothing is executed until you do a ToList() or .FirstOrDefault() or whatever. SO, you can use the queries in other queries, and it will create one big SQL statement when executed.

var query2 = from o in Orders
             where o.CustomerId == customerId
             && !o.OrderType.Equals("A")
             select o.OrderId;

var query3 = (from o in Orders
              join c in CustomerShip on o.CustShip equals c.ShipSeq 
              where c.CustomerId == customerId
              && !o.OrderStatus.Equals("A")
              && query2.Contains(o.OrderId)
              select c.ShipSeq).Distinct();

var query1 = from c in CustomerShip
             from i in query3
             where c.CustomerId == customerId
             && !c.Address.Contains("RETAIL")
             && !c.Address.Contains("STORE")
             && c.ShipSeq == i.ShipSeq
             orderby c.ShipTo descending, c.OrderDate descending
             select c;

However, I'm pretty sure you can reduce query2 and query3 down to just:

var query3 = (from o in Orders
              join c in CustomerShip on o.CustShip equals c.ShipSeq 
              where c.CustomerId == customerId
              && !o.OrderStatus.Equals("A")
              && !o.OrderType.Equals("A")
              select c.ShipSeq).Distinct();

Answer 2

Try something like this. I model some classes just for getting the error out. If you group by ShipSeq you don't need distinct. Just take first item from group will give same results.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication60
{
    class Program
    {
        static void Main(string[] args)
        {
            int customerID = 1234;
            List<Order> CustomTypeA = Order.orders
                .Where(x => (x.CustomerId == customerID) && (x.OrderType == "A") && (x.OrderStatus == "C")).ToList();

            var results = (from CustA in CustomTypeA 
                          join CustShip in Ship.CustomerShip on CustA.CustomerId equals CustShip.CustomerId 
                          select new { CustA = CustA, CustShip = CustShip})
                          .Where(x => (!RetailStore(x.CustShip.Address)) && (x.CustA.CustShip == x.CustShip.ShipSeq))
                          .OrderByDescending(x => x.CustShip.OrderDate)
                          .GroupBy(x => x.CustShip.ShipSeq)
                          .Select(x => x.FirstOrDefault())
                          .Select(x => new {
                              CustomerID = x.CustShip.CustomerId,
                              Address = x.CustShip.Address,
                              OrderDate = x.CustShip.OrderDate
                          }).ToList();

        }
        static Boolean RetailStore(string address)
        {
            string pattern = "RETAIL.*STORE";
            return Regex.IsMatch(address, pattern);
        }
    }
    public class Order
    {
        public static List<Order> orders = new List<Order>();

        public int CustomerId { get; set; }
        public string OrderType { get; set; }
        public string CustShip { get; set; }
        public string OrderStatus { get; set; } 
    }
    public class Ship
    {
        public static List<Ship> CustomerShip = new List<Ship>();

        public int CustomerId { get; set; }
        public string ShipSeq { get; set; }
        public string Address { get; set; }
        public DateTime OrderDate { get; set; }
     }
}

Answer 3

query2 and query3 Merged here into inner query

var Innerquery = (from o in Orders
              join c in CustomerShip on o.CustShip equals c.ShipSeq 
              where c.CustomerId == customerId
              && !o.OrderStatus.Equals("A")
              && !o.OrderType.Equals("A")
              select c.ShipSeq).Distinct();

var query1 = from c in CustomerShip
             from i in query3
             where c.CustomerId == customerId
             && innerquery.Contains(c.CustomerId)
             && !c.Address.Contains("RETAIL")
             && !c.Address.Contains("STORE")
             && c.ShipSeq == i.ShipSeq
             orderby c.ShipTo descending, c.OrderDate descending
             select c;

OR you can try Linqer http://www.sqltolinq.com

Answer 4

There could be many reasons why your query is slow in EF - I would suggest using a profiler.

The probable reasons are either EF creates an inefficient query (usually the database should create its own optimizations, but I have had bad experiences with EF and Oracle), or, depending on how many results it loads, mapping it to actual objects is very expensive.

In general, although seemingly not a popular opinion in the .NET world, I would suggest either creating a View, or using dbcontext.Database.SqlQuery<CustomerShip>(sql) whenever you have a complex query, especially when using Oracle, at least from my experiences with it in the past (has been some time, so I might be wrong.)