C# LINQ select from list

i have a list of event Ids returned from an xml document as shown below

public IEnumerable<EventFeed> 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<EventsDetails> 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<EventFeed> 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 => x.EventSortBy); } 

and this is the method to look up any matching eventIds in the XML that exist in my database

public IEnumerable<EventFeed> FilteredEvents(DateTime eventDate) { return GetAllEventsFromDatabase().Where(p => GetEventIds(eventDate).Contains<EventsDetails>(p.EventShowCode)); } 

the project fails to build with the following error:

Error 9 Argument '2': cannot convert from 'string' to 'Events.EventsDetails'

4 Answers

 var eventids = GetEventIdsByEventDate(DateTime.Now); var result = eventsdb.Where(e => eventids.Contains(e)); 

If you are returnning List<EventFeed> inside the method, you should change the method return type from IEnumerable<EventFeed> to List<EventFeed>.

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 => states.Any(s => x.State.Equals(s))).ToList(); 

I found this within the sample of CheckBoxList for nu-get.

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

Execute the GetEventIdsByEventDate() method and save the results in a variable, and then you can use the .Contains() method