C LINQ select from list

Question

i have a list of event Ids returned from an xml document as shown below  public IEnumerable lt EventFeed gt  GetEventIdsByEventDate DateTime eventDate                 return  from feed in xmlDoc Descendants  Show                   from ev in feed Elements  Event                   where Convert ToDateTime ev Attribute  Date   Value  ToShortDateString      eventDate ToShortDateString                   select new EventFeed                                         EventShowCode   feed Attribute  Code   Value                    ToList              i now need to query my database to match events that equal the eventIds returned from the above method  so i would have something like   select   from eventsdb where eventId in GetEventIdsByEventDate    how can i do this using LINQ    i cant seem to get any of the answers working   this is the method that looks up the eventIds from an XML feed  public IList lt EventsDetails gt  GetEventIds DateTime eventDate                 var eventids    from feed in xmlDoc Descendants  Show                           from ev in feed Elements  Event                           where Convert ToDateTime ev Attribute  Date   Value  ToShortDateString      eventDate ToShortDateString                           select new EventsDetails                                                         EventId   feed Attribute  Code   Value                            ToList             return eventids          this is the method that looks up the events in my database  public IEnumerable lt EventFeed gt  GetAllEventsFromDatabase                 var allEvents   from eventsList in GetEventsList                           select new EventFeed                                                         EventName   eventsList Title                              EventSummary   eventsList Introduction                              EventShowCode   eventsList EventId                              EventImageSmall   eventsList EventImageThumbUrl                              EventUrl   eventsList Url                              EventSortBy   eventsList SortOrder                                     return allEvents OrderBy x   gt  x EventSortBy           and this is the method to look up any matching eventIds in the XML that exist in my database  public IEnumerable lt EventFeed gt  FilteredEvents DateTime eventDate                 return GetAllEventsFromDatabase   Where p   gt  GetEventIds eventDate  Contains lt EventsDetails gt  p EventShowCode             the project fails to build with the following error   Error   9   Argument  2   cannot convert from  string  to  Events EventsDetails

User · Answer

Execute the GetEventIdsByEventDate   method and save the results in a variable  and then you can use the  Contains   method

User · Answer

In likeness of how I found this question using Google  I wanted to take it one step further  Lets say I have a string   states and a db Entity of StateCounties and I just want the states from the list returned and not all of the StateCounties   I would write   db StateCounties Where x   gt  states Any s   gt  x State Equals s    ToList      I found this within the sample of CheckBoxList for nu-get

User · Answer

var eventids   GetEventIdsByEventDate DateTime Now           var result   eventsdb Where e   gt  eventids Contains e      If you are returnning List lt EventFeed gt  inside the method  you should change the method return type from IEnumerable lt EventFeed gt  to List lt EventFeed gt

User · Answer

The  in  in Linq-To-Sql uses a reverse logic compared to a SQL query   Let s say you have a list of integers  and want to find the items that match those integers   int   numbers   new int     1  2  3  4  5  6  7  8  9     var items   from p in context Items                  where numbers Contains p ItemId                  select p    Anyway  the above works fine in linq-to-sql but not in EF 1 0  Haven t tried it in EF 4 0

[c#] C# LINQ select from list

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