c# - 如何使用 LINQ to SQL 执行 CROSS JOIN？

Question

如何使用 LINQ to SQL 执行 CROSS JOIN？

Answer 1

交叉连接只是两组的笛卡尔积。它没有明确的连接运算符。

var combo = from p in people
            来自汽车中的c
            选择新的
            {
                p.姓名，
                c.制作，
                c.型号，
                c.颜色
            };

Answer 2

与 Linq 扩展方法SelectMany（lambda 语法）相同：

var names = new string[] { "Ana", "Raz", "John" };
var numbers = new int[] { 1, 2, 3 };
var newList=names.SelectMany(
    x => numbers,
    (y, z) => { return y + z + " test "; });
foreach (var item in newList)
{
    Console.WriteLine(item);
}

Answer 3

根据史蒂夫的回答，最简单的表达方式是：

var combo = from Person in people
            from Car    in cars
            select new {Person, Car};

Answer 4

ATuple是笛卡尔积的好类型：

public static IEnumerable<Tuple<T1, T2>> CrossJoin<T1, T2>(IEnumerable<T1> sequence1, IEnumerable<T2> sequence2)
{
    return sequence1.SelectMany(t1 => sequence2.Select(t2 => Tuple.Create(t1, t2)));
}

Answer 5

扩展方法：

public static IEnumerable<Tuple<T1, T2>> CrossJoin<T1, T2>(this IEnumerable<T1> sequence1, IEnumerable<T2> sequence2)
{
    return sequence1.SelectMany(t1 => sequence2.Select(t2 => Tuple.Create(t1, t2)));
}

并使用如下：

vals1.CrossJoin(vals2)