Question

我做了很多搜索，并没有找到我想要的东西。我喜欢添加扩展方法，那么你如何使用扩展方法呢？

Answer 1

编写一些扩展方法，使其变得简单易用：

public class JoinResult<TL, TR>
{
    public TL Left { get; set; }
    public TR Right { get; set; }
}

public static IQueryable<JoinResult<TL, TR>> LeftJoin<TL, TR, TKey>(this IQueryable<TL> left, IQueryable<TR> right, Expression<Func<TL, TKey>> leftKeySelector, Expression<Func<TR, TKey>> rightKeySelector)
{
    return left
        .GroupJoin(right, leftKeySelector, rightKeySelector, (l, rightGroup) => new { l, rightGroup = rightGroup.DefaultIfEmpty() })
        .SelectMany(z => z.rightGroup.Select(r => new JoinResult<TL, TR> { Left = z.l, Right = r }));
}

public static IQueryable<JoinResult<TL, TR>> RightJoin<TL, TR, TKey>(this IQueryable<TL> left, IQueryable<TR> right, Expression<Func<TL, TKey>> leftKeySelector, Expression<Func<TR, TKey>> rightKeySelector)
{
    return right
        .GroupJoin(left, rightKeySelector, leftKeySelector, (r, leftGroup) => new { leftGroup = leftGroup.DefaultIfEmpty(), r })
        .SelectMany(z => z.leftGroup.Select(l => new JoinResult<TL, TR> { Left = l, Right = z.r }));
}

在LINQ和实体框架（方法）中执行左/右外连接的最佳方法是什么？

1 个答案: