How do I retrieve an item at an index using linq to entities

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//Hello people, I've tried several ways of going about this. My aim is to get some random questions from a question bank with distinct items. So I generated some random indexes based on the size of my question bank say 40 for example and get them stored in an array of integers. I now looped through the array to retrieve an item at the index of the array. I ended up receiving this error each time I try several ideas.

LINQ to Entities does not recognize the method 'CBTDLCF.QuestionTable ElementAtOrDefault[QuestionTable](System.Linq.IQueryable`1[CBTDLCF.QuestionTable], Int32)' method, and this method cannot be translated into a store expression.

C#

//This is what I wrote
public List<QuestionTable> RandomQuestionWIthDistinctElement()
{
     Random randIndex = new Random();
     int totalQuestions = context.QuestionTables.Count();
     int[] randomIndex = new int[totalQuestions];
     List<QuestionTable> d = new List<QuestionTable>();

     for (int i = 0; i < totalQuestions; i++)
     {
           randomIndex[i] = randIndex.Next(1,totalQuestions);
     }

     for (int i = 0; i < randomIndex.Distinct().Count(); i++)
     {
           var element = context.QuestionTables.ElementAt(index);
           d.Add(element);
     }

     return d;
}

//So I make use if the function in my Page_Load like this
//
var result = RandomQuestionWIthDistinctElement().Take(5).ToList();
questionTable = ToDataTable(result);//convert to sql datatable
//I don't know why I'm getting this error

Posted 7-Jul-15 7:37am

matmape

Updated 7-Jul-15 7:46am

virusstorm

v2

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virusstorm 7-Jul-15 13:47pm

Where exactly are you getting this error?

matmape 7-Jul-15 13:56pm

at var element = context.QuestionTables.ElementAt(index);

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virusstorm · Accepted Answer · 2015-07-07T08:08:00

Try:

C#

var element = context.QuestionTables.ToList()[index];

Basically, you are trying to get a specific row number in your table. There is no SQL equivalent (at least a simple way) to get this. Adding the .ToList() you are forcing an immediate execution of the query and bring the results into memory, specifically into a List object. This has a nice easy way to access the data via an index.

The issue with this is, if your table is large, you are bringing down a lot of data. Ideally, you should be querying the table based on a key or column in the source table.