LINQ GroupBy Count

Question

我的表包含EmployeeID，ProductID和ProductName。该表名为EmployeeProduct，我想进行查询（我将绑定到DataGrid），这将得到如下结果：

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

我试图通过此查询得到这样的信息，但它不会产生结果...... //更新 - 现在我尝试这样做，但仍然没有结果...... //

（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();
}

以后在代码中我想将它绑定到我的数据网格，但不幸的是它不会导致错误但是如果我这样做：

dg.ItemsSource = CountProducts();

它没有显示任何东西......

Answer 1

以下是几种方法：

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()
                    }));

Answer 2

我认为查询看起来像这样

  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()
                                         }