LINQ, can't join to string

Question

I have a list of users, each user has list of questions. In my model list of questions should be in string via comma. I try:

public List

        

Answer 1

can't include the string.Join() in the initial projection, because the LINQ translator doesn't support it. Can I write a custom translator for it?

Answer 2

Try using the Aggregate method.

Question4 = (from a in _dbContext.MultipleQuestions where a.MultipleQuestionType.KEY == MultipleQuestionKeys.BENEFITS select a.Question).ToArray().Aggregate((x,y) => x + "," + y)

Have not tested

Answer 3

I would suggest doing the string.Join operation locally instead using AsEnumerable:

var q = from i in _dbContext.Users
        where i.UserId != null
        select new
        {
            FirstName = i.FirstName,
            LastName = i.LastName,
            Question4Parts = _dbContext.MultipleQuestions
                                       .Where(a => a.MultipleQuestionType.KEY == 
                                                   MultipleQuestionKeys.BENEFITS)
                                       .Select(a => a.Question)
        };

return q.AsEnumerable()
        .Select(x => new ITW2012Mobile.ViewModels.AdminSurveyReportModel
                     {
                         FirstName = x.FirstName,
                         LastName = x.LastName,
                         Question4 = string.Join(", ", x.Question4Parts)
                     })
        .ToList();