左加入Linq到Entity的Vb.net

Question

我无法弄清楚linq到实体查询语法.我的问题是,如果Calls表的值为null然后出现注释,我想做一些类似于左连接的东西来从Calls表中获取'all'行.

我试图将它分组,但我无法弄清楚写它的正确方法.

Dim TicketQuery As ObjectQuery = From c In EnData.Customer _
                                         Join t In EnData.Calls On t.CustomerID Equals c.CustomerID _
                                         Join Status In EnData.Lists On t.Status Equals Status.ListValue _
                                         Join Project In EnData.Lists On t.Project Equals Project.ListValue _
                                         Join Priorty In EnData.Lists On t.Priority Equals Priorty.ListValue _
                                         Where c.Status > -1 And t.Status > -1 And Status.ListType = 1 And Project.ListType = 3 And Priorty.ListType = 2 _
         Select New With {c.CustName, t.CallID, t.CallDate, t.CallTime, t.Description, Key .Status = Status.ListText, Key .Project = Project.ListText, t.DateModified, Key .Priority = Priorty.ListText}

我该如何解决这个问题？

Answer 1

类似的问题:Linq to Sql:多个左外连接

Microsoft文档:http://msdn.microsoft.com/en-us/library/bb918093.aspx#Y916

LINQ示例来自:http://msdn.microsoft.com/en-us/vbasic/bb737909

左外连接可以用组连接表示所谓的外连接.左外连接类似于交叉连接,除了所有左侧元素至少包含一次,即使它们与任何右侧元素都不匹配.请注意即使没有匹配的产品,蔬菜也会出现在输出中.

Public Sub Linq105()
    Dim categories() = {"Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood"}

Dim productList = GetProductList()

Dim query = From c In categories _
            Group Join p In productList On c Equals p.Category Into Group _
            From p In Group.DefaultIfEmpty() _
            Select Category = c, ProductName = If(p Is Nothing, "(No products)", p.ProductName)

For Each v In query
    Console.WriteLine(v.ProductName + ": " + v.Category)
Next
End Sub