如何将以下 Linq 查询压缩为一个 IQueryable
我有一个 EntityFramework 模型，其中包含具有组织 EntityCollection 的用户实体。
对于特定用户，我尝试编写一个 Linq 查询来返回该用户所属组织的名称，其中该查询只会访问数据库一次。
我的问题是，我无法了解如何编写此查询，而不必先具体化用户，然后查询用户组织集合。
我想尝试编写一个查询数据库一次的查询。
到目前为止我所拥有的：
var orgNames = context.Users
.Where(u => u.LoweredUserName == userName.ToLower())
//materialises user
.FirstOrDefault()
.Organisations
//second hit to the db
.Select(o => o.Name);
我的伪目标是什么，但只见树木不见森林：
orgNames = context.Users
.Where(u => u.LoweredUserName == userName.ToLower())
//don't materialise but leave as IQueryable
.Take(1)
//The problem: turn what the query sees as possibly multiple
// (due to the Take method) EntityCollection<Organisation> into a List<String>
.Select(u => u.Organisations.Select(o => o.Name));
我看过聚合体，但我似乎在兜圈子:)
I have an EntityFramework model that has User entity that has an EntityCollection of Organisations.
For a particular User I am trying to write a Linq Query to return the names of the organisations that the user belongs where that query will hit the db only once.
My problem is that I cannot see how to write this query without having to materialise the user first then query the users organisation collection.
I would like to try and write one query that hits the db once.
What I have so far:
var orgNames = context.Users
.Where(u => u.LoweredUserName == userName.ToLower())
//materialises user
.FirstOrDefault()
.Organisations
//second hit to the db
.Select(o => o.Name);
What I was psuedo aiming for but cannot see the wood for the trees:
orgNames = context.Users
.Where(u => u.LoweredUserName == userName.ToLower())
//don't materialise but leave as IQueryable
.Take(1)
//The problem: turn what the query sees as possibly multiple
// (due to the Take method) EntityCollection<Organisation> into a List<String>
.Select(u => u.Organisations.Select(o => o.Name));
I have looked at aggregates but I seem to be going in circles :)
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哎哟！我想我可以通过使用 SelectMany 将集合的集合压缩为一个集合来回答我自己的问题，如下所示：
Doh! I think I can answer my own question by using SelectMany to condense the Collection of Collections into one collection like so:
我假设 Lowered User name 是唯一的，否则查询将毫无意义，因此您可以使用。
I'm assuming that Lowered User name is unique, otherwise the query would be fairly meaningless, so you can just use.