如何在 C# Linq 中按两个字段对数据进行分组？

Question

我有以下型号：

    public class User
    {
       public long Id { get; set; }
       public string? Name { get; set; }
       public string? Surname { get; set; }
       public string? PhoneNumber { get; set; }
       public IEnumerable<Sale>? Sales { get; set; }
    }

    public class Product
    {
       [Key]
       public int Id { get; set; }
       public string Name { get; set; }
       public decimal Price { get; set; }
       public IEnumerable<Sale>? Sales { get; set; }
    }
    
    public class Sale
    {
       public int Id { get; set; }
       public User? User { get; set; }
       public List<SaleItem> SaleItems { get; set; }
       public DateTime CreatedDt { get; set; }
    }

    public class SaleItem
    {
        public int Id { get; set; }
        public Sale? Sale { get; set; }
        public Product? Product { get; set; }
        public int Count { get; set; }
    }

需要按客户和产品分组的数量和价格。

我尝试通过以下方式解决问题：

var list = await context.SaleItems
    .Include(x => x.Product)
    .Include(x => x.Sale).ThenInclude(x => x.User)
    .Select(x => new
    {
        UserId = x.Sale.User.Id,
        UserName = x.Sale.User.Name,
        ProductId = x.Product.Id,
        ProductName = x.Product.Name,
        TotalCount = x.Count,
        TotalPrice = x.Product.Price * x.Count
    })
    .GroupBy(x => new { x.UserId, x.ProductId })
    .SelectMany(x => x)
    .ToListAsync();

但它不起作用。 谢谢！

Answer 1

SelectMany() 将返回列表列表的查询展平。

使用.Select(x => x) 而不是.SelectMany(x => x)。

您可以查看Difference Between Select and SelectMany以获得更详细的说明。