Sequence contains no elements

Question

I m currently using a single query in two places to get a row from a database   BlogPost post    from p in dc BlogPosts                  where p BlogPostID    ID                  select p  Single      The query is fine when retrieving the row to put data in to the text boxes  but it returns an error  Sequence contains no elements  when used to retrieve the row in order to edit it and put it back in to the database  I can t understand why it might find an appropriate row in one instance but not another    Using ASP NET MVC and LINQ

User · Answer

From  Fixing LINQ Error  Sequence contains no elements       When you get the LINQ error  Sequence contains no elements   this is usually because you are using the First   or Single   command rather than FirstOrDefault   and SingleOrDefault      This can also be caused by the following commands    FirstAsync   SingleAsync   Last   LastAsync   Max   Min   Average   Aggregate

User · Answer

In addition to everything else that has been said  you can call DefaultIfEmpty   before you call Single    This will ensure that your sequence contains something and thereby averts the InvalidOperationException  Sequence contains no elements   For example   BlogPost post    from p in dc BlogPosts                  where p BlogPostID    ID                  select p  DefaultIfEmpty   Single

User · Answer

I had a similar situation on a function that calculates the average   Example    ws Cells lastRow  startingmonths  Value   lstMediaValues Average      Case Solved    ws Cells lastRow  startingmonths  Value   lstMediaValues Count    0   0   lstMediaValues Average

User · Answer

Well  what is ID here  In particular  is it a local variable  There are some scope   capture issues  which mean that it may be desirable to use a second variable copy  just for the query   var id   ID  BlogPost post    from p in dc BlogPosts                  where p BlogPostID    id                  select p  Single      Also  if this is LINQ-to-SQL  then in the current version you get a slightly better behaviour if you use the form   var id   ID  BlogPost post   dc BlogPosts Single p   gt  p BlogPostID    id

User · Answer

Please use    FirstOrDefault     because if in the first row of the result there is no info this instruction goes to the default info

User · Answer

Reason for error    The query from p in dc BlogPosts where p BlogPostID    ID  select p returns a sequence  Single   tries to retrieve an element from the sequence returned in step1  As per the exception - The sequence returned in step1 contains no elements   Single   tries to retrieve an element from the sequence returned in step1 which contains no elements  Since Single   is not able to fetch a single element from the sequence returned in step1  it throws an error    Fix   Make sure the query  from p in dc BlogPosts where p BlogPostID    ID select p   returns a sequence with at least one element

User · Answer

This will solve the problem   var blogPosts    from p in dc BlogPosts              where p BlogPostID    ID              select p   if blogPosts Any        var post   post Single

[c#] Sequence contains no elements?

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