我有一个样本来研究Async调用,我需要从子查询中得到一个计数。我知道如何在 TSQL 查询中写这个,但我对 iqueryable 的使用有点困惑。
下面是我目前的情况。我正在获取用户,然后在一个循环中获取计数。我如何在第一个查询中完成循环部分?
public static async Task GetUsers(this List<UserViewModel> users)
{
var db = ApplicationDbContext.Create();
users.AddRange(await (from u in db.Users
select new UserViewModel
{
Id = u.Id,
Email = u.Email,
FirstName = u.FirstName,
LastName = u.LastName
}).OrderBy(o => o.Email).ToListAsync());
if (users.Any())
{
foreach(var user in users)
{
user.SubscriptionsCount = await (from us in db.UserSubscriptions
join s in db.Subscriptions on us.SubscriptionId equals s.Id
where us.UserId.Equals(user.Id)
select us).CountAsync();
}
}
}
可以用以下两种方式之一来处理。我已经选择了#2为我的例子。
var singleQuery = from u in db.Users
join sub in (from us in db.UserSubscriptions
join s in db.Subscriptions on us.SubscriptionId equals s.Id
group us by us.UserId into countGroup
select new { Count = countGroup.Count(), UserId = countGroup.Key })
on u.Id equals sub.UserId into sub1
from subR in sub1.DefaultIfEmpty()
select new UserViewModel
{
Id = u.Id,
Email = u.Email,
FirstName = u.FirstName,
LastName = u.LastName,
SubscriptionsCount = subR.Count == null ? 0 : subR.Count
};
var siteUsersSub = await (query).OrderBy(o => o.Email).ToListAsync();
var subQuery = from us in db.UserSubscriptions
join s in db.Subscriptions on us.SubscriptionId equals s.Id
group us by us.UserId into countGroup
select new { Count = countGroup.Count(), UserId = countGroup.Key };
var query = from u in db.Users
join sq in subQuery on u.Id equals sq.UserId into sq1
from sqR in sq1.DefaultIfEmpty()
select new UserViewModel()
{
Id = u.Id,
Email = u.Email,
FirstName = u.FirstName,
LastName = u.LastName,
SubscriptionsCount = sqR.Count == null ? 0 : sqR.Count
};
var siteUsers = await(query).OrderBy(o => o.Email).ToListAsync();