Why is this error Sequence contains no elements happening

Question

I am getting an Invalid Operation Exception  the stack is down below  I think it is because db Responses Where y   gt  y ResponseId Equals item ResponseId   First    is not returning any results  I checked the response data and the userResponseDetails has a ResponseId  I also just used a hard coded value  I also know that the statement that calls this one is adding the Responses row that this function should be calling    This was working about a month ago and I don t remember changing anything that would break this    InvalidOperationException  Sequence contains no elements     System Linq Enumerable First IEnumerable 1 source   269    System Data Objects ELinq ObjectQueryProvider  amp lt GetElementFunction amp gt b  0 IEnumerable 1 sequence   41    System Data Objects ELinq ObjectQueryProvider ExecuteSingle IEnumerable 1 query  Expression queryRoot   59    System Data Objects ELinq ObjectQueryProvider System Linq IQueryProvider Execute Expression expression   133    System Data Entity Internal Linq DbQueryProvider Execute Expression expression   87    System Linq Queryable First IQueryable 1 source   251    InSight Controllers ForecasterController userResponseDetails List 1 userResponseDetails   1039   Here is the offending code        HttpPost      public JsonResult userResponseDetails List lt ResponseDetailsPartial gt  userResponseDetails                 foreach  ResponseDetailsPartial item in userResponseDetails                        ResponseDetails temp   new ResponseDetails                temp ResponseId   item ResponseId              temp ResponseDetailVal   item ResponseDetailVal              temp QuestioChoicesId   item QuestioChoicesId              temp Response   db Responses                    Where y   gt  y ResponseId Equals item ResponseId   First                temp QuestionChoice   db QuestionChoices                     Where x   gt  x QuestionChoicesId Equals item QuestioChoicesId   First              db ResponseDetails Add temp                     db SaveChanges             return Json new   ResponseDetailsId   userResponseDetails    JsonRequestBehavior AllowGet           This is the AJAX that calls this specific action     ajax            type   POST            url    Forecaster userResponseDetails             data  JSON stringify rdetail            dataType   json            contentType   application json             and this is rdetail after it has been strigified      ResponseId  118  ResponseDetailVal  0 36  QuestioChoicesId  null

User · Accepted Answer

Check again  Use debugger if must  My guess is that for some item in userResponseDetails this query finds no elements    Where y   gt  y ResponseId Equals item ResponseId     so you can t call   First     on it  Maybe try    FirstOrDefault     if it solves the issue   Do NOT return NULL value  This is purely so that you can see and diagnose where problem is  Handle these cases properly

User · Answer

If this is the offending line   db Responses Where y   gt  y ResponseId Equals item ResponseId   First      Then it s because there is no object in Responses for which the ResponseId    item ResponseId  and you can t get the First   record if there are no matches   Try this instead   var response     db Responses Where y   gt  y ResponseId Equals item ResponseId   FirstOrDefault     if  response    null           take some alternative action   else     temp Response   response    The FirstOrDefault   extension returns an objects default value if no match is found  For most objects  other than primitive types   this is null

User · Answer

In the following line   temp Response   db Responses Where y   gt  y ResponseId Equals item ResponseId   First      You are calling First but the collection returned from db Responses Where is empty

[c#] Why is this error, 'Sequence contains no elements', happening?

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