Question

我正在尝试联接两个表，即基于产品表和商店表我的加入条件是产品ID，在这里我的查询总是返回0作为值

List<Store> list1 = new List<Store>();
List<Product> list2 = new List<Product>();

var query = list1.Join(
            list2,
            st => st.ProductId,
            Pd => Pd.productId,
            (st, Pd) => new
            {
                StoreName = st.storeName,
                StoreId = st.storeName,
                productId = st.ProductId,
                producRate = Pd.productRating

            }
          ).ToList();

Answer 1

您的数据或键的匹配方式似乎有问题：

internal class Program
{
    private static void Main(string[] args)
    {
        var products = Enumerable
            .Range(1, 10)
            .Select(i => new Product { ProductId = i, ProductRating = i / 2d })
            .ToList();

        var stores = Enumerable
            .Range(1, 10)
            .Select(i => new Store { ProductId = i + 5, StoreId = i + 100, StoreName = $"My Store {i}" })
            .ToList();

        var query = stores.Join(
            products,
            store => store.ProductId,
            product => product.ProductId,
            (store, product) => new
            {
                store.StoreName,
                store.StoreId,
                product.ProductId,
                product.ProductRating,
            });

        foreach (var item in query)
        {
            Console.WriteLine($"{item.ProductId} - {item.StoreId} - {item.StoreName} - {item.ProductRating}");
        }

        Console.WriteLine("Finished");
        Console.ReadKey();
    }
}

public class Product
{
    public int ProductId { get; set; }
    public double ProductRating { get; set; }
}

public class Store
{
    public int ProductId { get; set; }
    public int StoreId { get; set; }
    public string StoreName { get; set; }
}

输出：

6 - 101 - My Store 1 - 3
7 - 102 - My Store 2 - 3,5
8 - 103 - My Store 3 - 4
9 - 104 - My Store 4 - 4,5
10 - 105 - My Store 5 - 5
Finished

基于Lambda表达式的联接

1 个答案: