vb.net - Linq to Sql: Multiple left outer joins


I'm having some trouble figuring out how to use more than one left outer join using LINQ to SQL. I understand how to use one left outer join. I'm using VB.NET. Below is my SQL syntax.


    Orders o
    v.Id = o.VendorId
    s.Id = o.StatusId
    o.OrderNumber >= 100000 AND
    o.OrderNumber <= 200000

All Answers
  • Translate

    This may be cleaner (you dont need all the into statements):

    var query = 
        from order in dc.Orders
        from vendor 
        in dc.Vendors
            .Where(v => v.Id == order.VendorId)
        from status 
        in dc.Status
            .Where(s => s.Id == order.StatusId)
        select new { Order = order, Vendor = vendor, Status = status } 
        //Vendor and Status properties will be null if the left join is null

    Here is another left join example

    var results = 
        from expense in expenseDataContext.ExpenseDtos
        where expense.Id == expenseId //some expense id that was passed in
        from category 
        // left join on categories table if exists
        in expenseDataContext.CategoryDtos
                             .Where(c => c.Id == expense.CategoryId)
        // left join on expense type table if exists
        from expenseType 
        in expenseDataContext.ExpenseTypeDtos
                             .Where(e => e.Id == expense.ExpenseTypeId)
        // left join on currency table if exists
        from currency 
        in expenseDataContext.CurrencyDtos
                             .Where(c => c.CurrencyID == expense.FKCurrencyID)
        select new 
            Expense = expense,
            // category will be null if join doesn't exist
            Category = category,
            // expensetype will be null if join doesn't exist
            ExpenseType = expenseType,
            // currency will be null if join doesn't exist
            Currency = currency  

  • Translate

    Don't have access to VisualStudio (I'm on my Mac), but using the information from http://bhaidar.net/cs/archive/2007/08/01/left-outer-join-in-linq-to-sql.aspx it looks like you may be able to do something like this:

    var query = from o in dc.Orders
                join v in dc.Vendors on o.VendorId equals v.Id into ov
                from x in ov.DefaultIfEmpty()
                join s in dc.Status on o.StatusId equals s.Id into os
                from y in os.DefaultIfEmpty()
                select new { o.OrderNumber, x.VendorName, y.StatusName }

  • Translate

    I figured out how to use multiple left outer joins in VB.NET using LINQ to SQL:

    Dim db As New ContractDataContext()
    Dim query = From o In db.Orders _
                Group Join v In db.Vendors _
                On v.VendorNumber Equals o.VendorNumber _
                Into ov = Group _
                From x In ov.DefaultIfEmpty() _
                Group Join s In db.Status _
                On s.Id Equals o.StatusId Into os = Group _
                From y In os.DefaultIfEmpty() _
                Where o.OrderNumber >= 100000 And o.OrderNumber <= 200000 _
                Select Vendor_Name = x.Name, _
                       Order_Number = o.OrderNumber, _
                       Status_Name = y.StatusName

  • Translate

    In VB.NET using Function,

    Dim query = From order In dc.Orders
                From vendor In 
                dc.Vendors.Where(Function(v) v.Id = order.VendorId).DefaultIfEmpty()
                From status In 
                dc.Status.Where(Function(s) s.Id = order.StatusId).DefaultIfEmpty()
                Select Order = order, Vendor = vendor, Status = status 

  • Translate

    I think you should be able to follow the method used in this post. It looks really ugly, but I would think you could do it twice and get the result you want.

    I wonder if this is actually a case where you'd be better off using DataContext.ExecuteCommand(...) instead of converting to linq.

  • Translate

    I am using this linq query for my application. if this match your requirement you can refer this. here i have joined(Left outer join) with 3 tables.

     Dim result = (From csL In contractEntity.CSLogin.Where(Function(cs) cs.Login = login AndAlso cs.Password = password).DefaultIfEmpty
                       From usrT In contractEntity.UserType.Where(Function(uTyp) uTyp.UserTypeID = csL.UserTyp).DefaultIfEmpty ' <== makes join left join
                       From kunD In contractEntity.EmployeeMaster.Where(Function(kunDat) kunDat.CSLoginID = csL.CSLoginID).DefaultIfEmpty
                       Select New With {
                      .CSLoginID = csL.CSLoginID,
                      .UserType = csL.UserTyp}).ToList()