c# - LINQ GroupBy 计数

Question

我有一个表，其中包含 EmployeeID、ProductID 和 ProductName。该表称为 EmployeeProduct，我想进行查询(我将其绑定(bind)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

我试图通过这个查询得到这样的东西，但它没有结果......//已更新 - 现在我尝试这样做，但仍然没有结果...//

(首页.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();
}

稍后在代码中我想将其绑定(bind)到我的数据网格，但不幸的是它不会导致错误，但如果我这样做:

dg.ItemsSource = CountProducts();

它没有显示任何东西......

Answer 1

这里有几种方法可以做到这一点:

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()
                    }));