C# 如果表中存在行，如何合并

我在下面的声明中加入了3个表：

var data = from x in dbContext.Base_Agencies
                   from u in dbContext.Base_AgencyInstances
                   from o in dbContext.Payment2Account_SecurityRuleAgencies
                   where u.AgencyId == x.AgencyId
                   where o.AgencyId == x.AgencyId
                   where u.AgencyInstanceId == param.AgencyInstanceId
                   select new RsSecurityParamsResult
                   {
                       AgencyId = x.AgencyId,
                       AgencyNameView = u.AgencyNameView,
                       Stamp = u.Stamp,
                       Pni = x.Pni,
                       Prefix = u.Prefix,
                       ServiceEnabled = o.ServiceEnabled,
                       DisabledDateTime = o.DisabledDateTime,
                       AmountHourTresholdWarning = o.AmountHourTresholdWarning,
                       AmountHourTresholdStop = o.AmountHourTresholdStop,
                       CountHourTresholdWarning = o.CountHourTresholdWarning,
                       CountHourTresholdStop = o.CountHourTresholdStop
                   };

---

问题是，在某些示例中，表“o”中没有代理行。在这种情况下，我只想从其他表中选择值，除了“o”表。我该怎么做呢？

我想你可能想做一个

左外连接

var data = from x in dbContext.Base_Agencies
                   join u in dbContext.Base_AgencyInstances 
                   on u.AgencyId == x.AgencyId
                   join o in dbContext.Payment2Account_SecurityRuleAgencies 
                   on o.AgencyId == x.AgencyId into lrs
                   from lr in lrs.DefaultIfEmpty()
                   select new RsSecurityParamsResult
                   {
                       AgencyId = x.AgencyId,
                       AgencyNameView = u.AgencyNameView,
                       Stamp = u.Stamp,
                       Pni = x.Pni,
                       Prefix = u.Prefix,
                       ServiceEnabled =  lr.ServiceEnabled ?? "Default",
                        ...... // other code similar ........
                   };

正确的解决方案是：

  var data = from x in dbContext.Base_Agencies
                   join u in dbContext.Base_AgencyInstances
                   on  x.AgencyId equals u.AgencyId
                   join o in dbContext.Payment2Account_SecurityRuleAgencies
                   on x.AgencyId equals o.AgencyId into lrs
                   from lr in lrs.DefaultIfEmpty()
                   where u.AgencyInstanceId == param.AgencyInstanceId

                   select new RsSecurityParamsResult
                   {
                       AgencyId = x.AgencyId,
                       AgencyNameView = u.AgencyNameView,
                       Stamp = u.Stamp,
                       Pni = x.Pni,
                       Prefix = u.Prefix,
                       ServiceEnabled = lr.ServiceEnabled,
                       DisabledDateTime = lr.DisabledDateTime,
                       AmountHourTresholdWarning = lr.AmountHourTresholdWarning ,
                       AmountHourTresholdStop = lr.AmountHourTresholdStop,
                       CountHourTresholdWarning = lr.CountHourTresholdWarning ,
                       CountHourTresholdStop = lr.CountHourTresholdStop
                   };

您所说的表“o”中没有代理行是什么意思？情况：1。在表“x”中，有一行包含一些agencyId，2。在表“u”中，有一行具有相同的agencyId 3。在表“o”中，没有一行具有相同的agencyIdyeah，您可能需要检查后面的答案。您的答案中有几个语法错误，但主要思想是正确的，这对我帮助很大。