嵌套枚举上的GroupBy

请尝试以下查询:

var query =
    from a in Activities
    from b in a.Businesses
    group new { a, b } by b.Id into g
    select new 
    {
        Business = g.Select(x => x.b).First(),
        Activities = g.Select(x => x.a).ToList()
    };

var result = query.ToList();

这样可以:

它获得了所有独特的业务,然后从中创建具有包含此业务的所有活动的组:

var result = activities
    .SelectMany(a => a.Businesses)
    .DistinctBy(b => b.Id)
    .GroupBy(
        b => b,
        b => activities.Where(a => a.Businesses.Any(ab => ab.Id == b.Id)));

注意:我还假设 Id 是它应该分组的属性。

以下内容应该有效:

var businesses = activities
    //flatten the structure for every business
    //for every entry create a new object that contains the activity and business
    .SelectMany(x => x.Businesses, (activity, business) => new { activity, business })
    //group by the business id and for each id select all activities
    .GroupBy(x => x.business.Id, x => x.activity)
    //materialize the enumerable (not required)
    .ToList();