左加入Linq到实体的Vb.net

我无法弄清楚linq实体查询语法。我的问题是，如果Calls表的值为null，那么注意到了，我想让左连接类似于Calls表中的'all'行。左加入Linq到实体的Vb.net

我试图对它进行分组，但我无法弄清楚它的正确写法。

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}

我该如何解决呢？

来源

2011-04-11 Ezi

你能解释这些数据，您希望看到使用组结果？ – Jeremy 2011-04-12 02:07:30

如果你创建Dummy类，你可以在LINQPad中测试你的LINQ http://www.linqpad.net/ – Jeremy 2011-04-12 04:14:45

类似的问题：Linq to Sql: Multiple left outer joins

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

LINQ例子：http://msdn.microsoft.com/en-us/vbasic/bb737909

左外连接所谓的外连接可以用一组表示加入。左外连接像交叉连接一样，除了所有左侧元素至少包含一次，即使它们不匹配任何右侧元素。请注意蔬菜如何在产出中出现，即使它没有匹配的产品。

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

来源

2011-04-12 02:37:38 Jeremy

对于左连接VB.net中，我们可以用我们

Dim q = 
    (From item In _userProfileRepository.Table 
    Let Country = (From p In _countryRepository.Table Where p.CountryId = item.CurrentLocationCountry Select p.Name).FirstOrDefault 
    Let State = (From p In _stateRepository.Table Where p.CountryId = item.CurrentLocationCountry Select p.Name).FirstOrDefault 
    Let City = (From p In _stateRepository.Table Where p.CountryId = item.CurrentLocationCountry Select p.Name).FirstOrDefault 
    Where item.UserId = item.ProfileId.ToString)

后，左连接，我们可以通过

Dim q2 = 
    (From p In q Group p By p.Country, p.State, p.City Into Group 
    Select New With 
     { 
      .Country = Country, 
      .State = State, 
      .City = City, 
      .Count = Group.Count 
     }).ToList()

来源

2015-02-13 01:52:06 Mirak

左加入Linq到实体的Vb.net

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