将具有 2 个“左联接”和多条件的 Sql 查询转换为实体框架查询

Question

我试图转换这个 sql 查询

Select * 
from (
    select SenDa.*,Prod.ProductKHK,FCod.FailCodeDesc  
    from databa.dbo.SensorData as SenDa 
    left join Products as Prod on SenDa.ProductID = Prod.ProductID
    left join FailCodes as FCod on SenDa.FailCode = FCod.FailCode and (FCod.ProdLineID =0 or FCod.ProdLineID = FCod.ProdLineID)
) as SenDa

到 sql Linq 所以：

var SensDatJoinFail = (from SensDat in Jas_en.SenDatas
join Prod in Jas_en.Products on 
SensDat.ProductID equals Prod.ProductID
join FCod in Jas_en.FailCodes on SensDat.FailCode equals FCod.FailCode1
where FCod.ProdLineID == 0 || FCod.ProdLineID == FCod.ProdLineID

                               select new
                          {
                              Serial_No = SensDat.Serial_No,
                              OrderID = SensDat.OrderID,
                              Artikelnummer = Prod.ProductKHK,
                              StartProcTime = SensDat.StartProcTime,
                              EndProcTime = SensDat.EndProcTime,
                              Packaged = SensDat.Packaged,
                              Labeled = SensDat.Labeled,
                              Reworked = SensDat.Reworked,
                              LastStation = SensDat.LastStation,
                              FailCode = SensDat.FailCode,

                              FailCodeDesc = FCod.FailCodeDesc,

                          });

但我在行数中的查询结果有所不同

不知道，问题出在哪里？

Answer 1

这是一个 EF 常见问题解答。不要在 LINQ to Entitites 中使用 JOINS。只需导航您的导航属性。比如：

   from SensDat in Jas_en.SenDatas
    select new
    {
      Serial_No = SensDat.Serial_No,
      OrderID = SensDat.OrderID,
      Artikelnummer = SensDat.Product.ProductKHK,
      StartProcTime = SensDat.StartProcTime,
      EndProcTime = SensDat.EndProcTime,
      Packaged = SensDat.Packaged,
      Labeled = SensDat.Labeled,
      Reworked = SensDat.Reworked,
      LastStation = SensDat.LastStation,
      FailCode = SensDat.FailCode,
      FailCodeDesc = SensDat.FailCode.FailCodeDesc,
    });

Answer 2

您获得的行数减少了，因为您使用的是 inner 联接而不是 left 联接。试试这样的：

var result= from table1 in dbo.Table1 
            from table2 in dbo.Table2
                           .Where(i=>i.Id == table1.Id)
                           .DefaultIfEmpty();

或者你可以看看如何Perform left outer joins

    Person magnus = new Person { FirstName = "Magnus", LastName = "Hedlund" };
    Person terry = new Person { FirstName = "Terry", LastName = "Adams" };
    Person charlotte = new Person { FirstName = "Charlotte", LastName = "Weiss" };
    Person arlene = new Person { FirstName = "Arlene", LastName = "Huff" };

    Pet barley = new Pet { Name = "Barley", Owner = terry };
    Pet boots = new Pet { Name = "Boots", Owner = terry };
    Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
    Pet bluemoon = new Pet { Name = "Blue Moon", Owner = terry };
    Pet daisy = new Pet { Name = "Daisy", Owner = magnus };

    // Create two lists.
    List<Person> people = new List<Person> { magnus, terry, charlotte, arlene };
    List<Pet> pets = new List<Pet> { barley, boots, whiskers, bluemoon, daisy };

    var query = from person in people
                join pet in pets on person equals pet.Owner into gj
                from subpet in gj.DefaultIfEmpty()
                select new { person.FirstName, PetName = subpet?.Name ?? String.Empty };