CODEWITHSUNDEEP
asp.net-mvc-3linq-to-entitiesdevexpress
Dawid Dziadkiewicz
Dawid Dziadkiewicz

Reputation: 556

How to aggregate string using Linq 2 Entities

I have an IQueryable<Model> of objects in my db. I need to cast them to IQueryable<ViewModel>

class Model 
{
    public Guid ModelId { get; set; }

    // some properties

    public virtual User Users{ get; set; }

}

class User
{
    public Guid UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

class ViewModel
{
    public Guid ModelId { get; set }
    public string UsersName { get; set; }
}

ViewModel.UsersName should be merged string of all users first and last names. This need to be a IQueryable since I'll use DevExpress Mvc Grid and I'll need to pass it in this way. Grid handles the paging, so it needs to IQueryable.

I've tried:

IQueryable<ViewModel> viewModel = model.Select(s => new ViewModel()
        {

            UsersName = s.Users
                .OrderBy(d => d.LastName)
                .ThenBy(d => d.FirstName)
                .Aggregate(string.Empty, (s1, users) => users.FirstName + ' ' + users.Surname + ", ")
        });

but it's not translatable to linq to entities. I've also tried string.join() but it won't work neither.

The result string should be for expample : "Cecelia Leblanc, Sarah Hodge" ... etc.

Thanks for any input.

Upvotes: 0

Views: 571

Answers (1)

Gert Arnold
Gert Arnold

Reputation: 109118

Usually view models/DTOs should not be too smart, but this is a case where a little bit of smartness comes in too handy for comfort. Create a view model like:

class ViewModel
{
    public Guid ModelId { get; set; }
    public IEnumerable<string> UserNames { get; set; }
    public string UserNamesString
    {
        get { return string.Join(", ", this.UserNames); }
    }
}

populate it by

var models = s.Models.Select(m => new ViewModel
                        { ModelId = m.ModelId,
                          UserNames = m.Users
                                       .OrderBy(d => d.LastName)
                                       .ThenBy(d => d.FirstName)
                                       .Select(u => u.FirstName + ' ' 
                                                  + u.Surname)
                        }).ToList();

and access the UserNamesString property from models.AsQueryable().

Upvotes: 2

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