Inline Select with LINQ

Question

I need to replicate a T-SQL statement that has an inner select, using LINQ:

SELECT *, 
CustomerTypes.Description as CustomerType, 
(Select Min(Distinct DocumentStatistics.StatDateTime) As LastStatCheck
From DocumentStatistics
Where DocumentStatistics.CustomerId = Customers.CustomerId) As LastStatCheck 
FROM Customers 
INNER JOIN CustomerTypes ON Customers.CustomerTypeID = CustomerTypes.CustomerTypeID 
ORDER BY CustomerName

The following is the closest I was able to come, but it ends up returning all of the DocumentStatistics, 40,000 plus.

            Dim docQuery = (From doc In data.DocumentStatistics _
                       Select doc)

        Dim query = From customer In data.Customers _
                    Join docStat In docQuery _
                    On customer.CustomerID Equals docStat.CustomerID _
                    Select Customer = customer, LastStatCheck = _
                        (From doc In docQuery Where customer.CustomerID = doc.CustomerID _
                        Select doc.StatDateTime).Distinct().Min()

What am I missing? How do I replicate the initial SQL statement?

I can take VB or C# examples, and I am working with SQL Server database.

Answer 1

John,

Check out a product named Linqer (I have no association with this product). It takes a SQL statement and converts it to LINQ. It's able to convert almost any query you throw at it. It's been very useful to me. It's also taught me a lot about how LINQ works.

Randy

Answer 2

What you really want is a group join.

C# Example:

var query = from c in data.Customers
            join ds in data.DocumentStatistics
            on c.CustomerID equals ds.CustomerID into stats
            select new
            {
                Customer = c,
                LastStatCheck = stats.Min(s => s.StatDateTime)
            };

Answer 3

You need to use the Group Join function to achieve this, something like the following in C#:

var result = from customer in data.Customers
             join docStat in data.DocumentStatistics
                    on customer.CustomerID equals docStat.CustomerID into stats
             where stats.Count() > 0
             select new
             {
                 Customer = customer,
                 LastStatCheck = stats.Min(res => res.StatDateTime)
             };

and in VB.Net

Dim result = From customer In data.Customers _
             Group Join docStat In data.DocumentStatistics _
                  On customer.CustomerID Equals docStat.CustomerID Into stats = Group _
             Where stats.Count() > 0 _
             Select New With _
             { _
                 .Customer = customer _
                 .LastStatCheck = stats.Min(Function(res) res.StatDateTime) _
             }

Answer 4

Linqer gave me the following results from my original SQL statement:

From customer In data.Customers _
                    Select _
                    Customer = customer, _
                    LastStatCheck = (CType((Aggregate lastDateChecked In _
                    (From docStat In data.DocumentStatistics _
                    Where docStat.CustomerID = customer.CustomerID _
                    Select docStat) Into Min(lastDateChecked.StatDateTime)), DateTime?))

The helpful thing about Linqer was that I can put the t-SQL statement in and run the query next to the LINQ statement.