LINQ to Entities does not recognize the method 'Char get_Chars(Int32)' method, and this method cannot be translated into a store expression

Question

I would like to select only the records that have the field "1" from the string eventTriggers (that looks something like this : "00100010" )

I've tried and succesfully done so with more than 1 calls .. but i doubt its efficient. Basically I would want something like this ... but apprently LINQ does not support this.
(LINQ to Entities does not recognize the method 'Char get_Chars(Int32)' method, and this method cannot be translated into a store expression.)

     using (var service = new dB.Business.Service.BaseBusinessService<memo>())
   {
      List<memo> result = service.Repository.GetQuery().Where(p => p.ID == ID && p.eventTriggers[index] == '1').ToList();
   }

Any hints towards the correct solution ? Thank you !

Answer 1

EF can't convert the char array operation into a valid query. How about

IEnumerable<Memo> memos
using (var service = new dB.Business.Service.BaseBusinessService<Memo>())
{
    memos = service.Repository.GetQuery()
                    .Where(p => p.ID == ID).AsEnumerable();
}

var result = memos.Where(m => m.eventTriggers[index] == '1').ToList();

This gets all the memos with a matching ID locally then filters on the eventTriggers array.

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Alternatively you could convert eventTriggers into a numeric value and use a bit mask, this would probably be a much faster query.

Linq looking like this,

using (var service = new dB.Business.Service.BaseBusinessService<Memo>())
{
    result = service.Repository.GetQuery()
                 .Where(p => 
                         p.ID == ID
                     &&
                         m.eventTriggers & mask != 0).ToList();
}

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more exapmles here