LINQ GroupBy Count | 易学教程

问题

I've got table which contains of EmployeeID, ProductID and ProductName. The table is called EmployeeProduct and I'd like to make query (which I'll bind to DataGrid) which will get me a result like this:

Employee ID| ProductID | Name | Count(ProductID)
   1       |     2     | XYZ  | 3
   1       |     5     | ZXY  | 2
   2       |     2     | XYZ  | 1

I tried to get sth like this by this query, but it doesn't take a result... // UPDATED - Now I try to do this this way, but still have no result... //

(Home.xaml.cs)

public class ProductCount
{
    public int ProductNumber { get; set; }
    public int EmployeeNumber { get; set; }
    public int CountProducts { get; set; }
}

public IQueryable<ProductCount> CountProducts()
{
    var data = from b in _employ.EmployeeProduct
        group b by new { b.EmployeeID, b.ProductID } int z
        select new ProductCount { EmployeeNumber = z.Key.EmployeeID, ProductNumber = z.Key.ProductNumber, CountProducts = z.Count()};
    return data.AsQueryable();
}

and later in code I'd like to bind this to my datagrid, but unfortunately it don't causes error but if I do this:

dg.ItemsSource = CountProducts();

it doens't show anything ...

回答1:

Here's a couple of way to do this:

var employeeProducts = new List<EmployeeProduct>();
employeeProducts.Add(new EmployeeProduct(1, 2, "XYZ"));
employeeProducts.Add(new EmployeeProduct(1, 5, "ZXY"));
employeeProducts.Add(new EmployeeProduct(2, 2, "XYZ"));

var way1 = employeeProducts.Select(
    ep => new ProductCount
                {
                    ProductNumber = ep.ProductID,
                    EmployeeNumber = ep.EmployeeID,
                    CountProducts = employeeProducts.Count(epc => epc.ProductID == ep.ProductID)
                });

var way2 = employeeProducts
    .GroupBy(ep => ep.ProductID)
    .SelectMany(epg => epg.Select(
        ep => new ProductCount
                    {
                        ProductNumber = ep.ProductID,
                        EmployeeNumber = ep.EmployeeID,
                        CountProducts = epg.Count()
                    }));

回答2:

I'm thinking the query will look something like this

  EntityQuery<EmployeeProduct> query = from c in _employ.CountProduct()
                                         group c by new {c.UserId, c.ProductId, c.Name}
                                         into g
                                         select new {
                                            g.UserId,
                                            g.ProductId,
                                            g.Name,
                                            Count = g.Count()
                                         }

来源：https://stackoverflow.com/questions/8919100/linq-groupby-count

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