计算字段属性出现在列中的次数

Question

I'm trying to count how many times a value appears in a column on my table using Lambda or Linq.

Here's my Table properties

public class Vote
{
    [Key]
    public int VoteId { get; set; }

    public int CandidateId { get; set; }

    public int CategoryId { get; set; }

    public string Id { get; set; }
    public int ParticipantId { get; set; }
    public DateTime datecreated { get; set; }
}

So in my controller I'm doing this

public ActionResult Index(int? CategoryId, string Id)
{
    List<VoteCan> agc = new List<VoteCan>();
    if(CategoryId.HasValue)
    {
        var allcategory = db.Votes.ToList().FindAll(x => (x.CategoryId == CategoryId.Value) && (x.Id == Id)).ToList();
        //I want to count how many Candidates are in the Votes table using the candidateId
    }

    return View();
}

For example I want to have something like this

CandidateNo      Count
21358              3
21878              4

Answer 1

You need to group by CategoryId . Use GroupBy :-

List<VoteCan> results = db.Votes.GroupBy(x => x.CandidateId)
                      .Select(x => new VoteCan
                                  {
                                      CandidateNo = x.Key,
                                      Count = x.Count()
                                  }).ToList();

Assuming VoteCan class has CandidateNo & Count properties.