Linq results different than the sql result - sql-server

Question

I am having an MVC4 web application where I am using LINQ.
I have the below query which results 53 rows in SQL.
select * from table1 t join
[table2] tpf on t.TestID=tpf.TestID
join
table3 pf on tpf.Test2ID =pf.Test2ID
join table4 pfp on
pf.Test3ID = pfp.Test3ID
join table5 p on pfp.Test5ID = p.Test5ID where t.testtypeid=1
order by pfp.Test3ID,pf.Test2ID
If I convert the same query as below it returns more records.
trvm.MyTestVMs = (
from tt in db.table1s
join ttpf in db.table2s on tt.TestID equals ttpf.TestID
join pf in db.table3s on ttpf.Test2ID equals pf.Test2ID
join pfp in db.table4s on pf.Test3ID equals pfp.Test3ID
join p in table5s on pfp.Test5ID equals p.Test5ID
where tt.testtypeid == 1
orderby pfp.Test3ID
orderby pf.Test2ID
select new MyTestVM
{
FamilyID = pf.Test2ID,
ProductID = p.Test3ID,
Desc = p.Description
}
).ToList();
The result which is getting from SQL and the above LINQ varies. Actually, there are some duplicate result I am getting from the LINQ query. What is causing this difference?

Answer 1

It turns out that the LINQ query is not equivalent to the SQL query posted due to the usage of a products query variable (not shown in the post) which causes one of the many-to-many link table to be included twice, thus producing more records.
One way to fix the problem is to replace products with db.Products and apply the same filters as in the query variables you were trying to reuse.
But if you want to reuse query variables, then here is the correct way to do that:
// Eliminate the need of DbFunctions.TruncateTime(dt) inside the queries
dt = dt.Date;
// Queries
var productFamilys = (
from tt in db.TestTypes
join ttpf in db.TestTypeProductFamilys on tt.TestTypeID equals ttpf.TestTypeID
join pf in db.ProductFamilys on ttpf.ProductFamilyID equals pf.ProductFamilyID
where tt.TestTypeID == TestTypeID
where DbFunctions.TruncateTime(pf.StartDate) <= dt
where DbFunctions.TruncateTime(pf.EndDate) > dt
select pf
);
var productFamilyProducts = (
from pf in productFamilys
join pfp in db.ProductFamilyProducts on pf.ProductFamilyID equals pfp.ProductFamilyID
join p in db.Products on pfp.ProductID equals p.ProductID
where DbFunctions.TruncateTime(p.StartDate) <= dt
where DbFunctions.TruncateTime(p.EndDate) > dt
select new { Family = pf, Product = p }
);
var products = (
from pfp in productFamilyProducts
select pfp.Product
);
var productFamilyProductVMs = (
from pfp in productFamilyProducts
orderby pfp.Product.ProductID, pfp.Family.ProductFamilyID
select new ProductFamilyProductVM
{
ProductFamilyID = pfp.Family.ProductFamilyID,
ProductID = pfp.Product.ProductID,
ProdDesc = pfp.Product.Description
}
);
// Results
trvm.ProductFamilys = productFamilys.ToList();
trvm.Products = products.ToList();
trvm.ProductFamilyProductVMs = productFamilyProductVMs.ToList();
Now the SQL for the last query (the one in question) looks like this
SELECT
[Project1].[ProductFamilyID] AS [ProductFamilyID],
[Project1].[ProductID] AS [ProductID],
[Project1].[Description] AS [Description]
FROM ( SELECT
[Extent2].[ProductFamilyID] AS [ProductFamilyID],
[Extent4].[ProductID] AS [ProductID],
[Extent4].[Description] AS [Description]
FROM [dbo].[TestTypeProductFamilies] AS [Extent1]
INNER JOIN [dbo].[ProductFamilies] AS [Extent2] ON [Extent1].[ProductFamilyID] = [Extent2].[ProductFamilyID]
INNER JOIN [dbo].[ProductFamilyProducts] AS [Extent3] ON [Extent2].[ProductFamilyID] = [Extent3].[ProductFamilyID]
INNER JOIN [dbo].[Products] AS [Extent4] ON [Extent3].[ProductID] = [Extent4].[ProductID]
WHERE ([Extent1].[TestTypeID] = #p__linq__0) AND ((convert (datetime2, convert(varchar(255), [Extent2].[StartDate], 102) , 102)) <= #p__linq__1) AND ((convert (datetime2, convert(varchar(255), [Extent2].[EndDate], 102) , 102)) > #p__linq__2) AND ((convert (datetime2, convert(varchar(255), [Extent4].[StartDate], 102) , 102)) <= #p__linq__3) AND ((convert (datetime2, convert(varchar(255), [Extent4].[EndDate], 102) , 102)) > #p__linq__4)
) AS [Project1]
ORDER BY [Project1].[ProductID] ASC, [Project1].[ProductFamilyID] ASC
i.e. pretty similar to the sample SQL query and should produce the same results.

Answer 2

Result is different because in your second query , you have two "OrderBy" and because of that, the second OrderBy it's works over the collection which is result of first "OrderBy" and is reordering the items.
Change
orderby pfp.ProductID
orderby pf.ProductFamilyID
from your second query in
orderby pfp.ProductID, pf.ProductFamilyID
to get same results