asp.net - 剩下的多个表使用Linq连接

Question

我知道Linq的左连接类似这样:

var q=from e in db.Employes　　　 
      join o in db.Orders on e equals o.Emoloyee into ords　　
      from on in ords.DefautIfEmpty()
      select new
      {　　　　　　
         e.FirstName,　　　　　
         e.LastName　　　
　     };

那么多重联接呢？这是我的代码

var personalInfoQuery = from t in crnnsupContext.Tombstones
                        join p in crnnsupContext.ProvStates on t.ProvinceState equals p.ProvinceStateID 
                        join n in crnnsupContext.NursingSchools on t.NursingSchool equals n.SchoolID 
                        join i in crnnsupContext.InitialEducations on t.InitialEducation equals SqlFunctions.StringConvert((double)i.InitalEducationID, 1)
                        join g in crnnsupContext.tbl_GraduatedProvCountry on t.GradPovCountry equals g.id
                        where t.RegNumber == _username
                        select new CPersonalInfo
                        {
                            ProvState = p,
                            Tombstone = t,
                            NursingSchool = n,
                            InitialEducation = i,
                            GraduatedProvCountry = g,
                         };

每个联接表都可以具有“null”字段。有什么可以帮助我的，谢谢

Answer 1

多连接看起来应该很相似-变得很冗长，但我会尝试一下。
您可能还需要在最后的where行中进行一些null检查。

var personalInfoQuery = from t in crnnsupContext.Tombstones
                        join p in crnnsupContext.ProvStates on t.ProvinceState equals p.ProvinceStateID into group1
                        from g1 ini group1.DefaultIfEmpty()
                        join n in crnnsupContext.NursingSchools on g1.NursingSchool equals n.SchoolID into group2
                        from g2 in group2.DefaultIfEmpty()
                        join i in crnnsupContext.InitialEducations on g2.InitialEducation equals SqlFunctions.StringConvert((double)i.InitalEducationID, 1) into group3
                        from g3 in group3.DefaultIfEmpty()
                        join g in crnnsupContext.tbl_GraduatedProvCountry on g3.GradPovCountry equals g.id into group4
                        from g4 in group4.DefaultIfEmpty()
                        where g4 == null || g4.RegNumber == _username
                        select new CPersonalInfo
                        {
                            ProvState = p,
                            Tombstone = t,
                            NursingSchool = n,
                            InitialEducation = i,
                            GraduatedProvCountry = g,
                         };

似乎还有另一种进行外部联接的方法，但是没有进行任何测试的方法，我什至不确定在这种情况下是否可以使用它-如果您有兴趣，请查看这篇文章的答案:
outer join in linq