如果 table 中的行存在，如何合并

Question

我在下面的语句中加入了 3 tables:

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 table 'o' 中不会有代理行。在这种情况下，我只想 select 来自其他 table 的值，'o' table 除外。我应该怎么做？

Answer 1

我想你可能想要LEFT OUTER JOIN像

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 ........
                   };

Answer 2

正确的解法是：

  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
                   };

如果 table 中的行存在，如何合并

How to merge if row in table exists

c#

linq

entity