如何在 Nhibernate 中对子集合进行 QueryOver

Question

您好，我有一个名为 Notifications 的类，它是用户的子类。

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string UserName { get; set; }
    public ICollection<UserNotification> UserNotifications { get; set; }
}

public class Notification
{
    public int Id { get; set; }
    public ICollection<UserNotification> UserNotifications { get; set; }
    public string Title { get; set; }
    public string Message { get; set; }
    public bool IsRead { get; set; }
    public DateTime CreatedDate { get; set; }
}

public class UserNotification
{
    public User User { get; set; }
    public Notification Notification { get; set; }
}

现在我想通过 ID 获取用户，它将为当前用户带来所有通知。

var user = NhSession.Get<User>(userId);

但我不想收到所有通知。我只想让用户收到未读通知，只想为用户获取top 5 (Latest) notifications。

我试图通过 joinQueryOver 来实现，但我无法做到。任何人都可以建议让这个工作。

Answer 1

基于最新的更新和新的Entity(ies)结构，我们现在可以从Pairing对象中获利，并快速选择有类似这样未读Notificaitons的用户

查找未阅读通知的用户

var session = NHSession.GetCurrent();
Notification notification = null;
UserNotification pair = null;
User user = null;

var subquery = QueryOver.Of<UserNotification>(() => pair)
    // this will give us access to notification
    // see we can filter only these which are NOT read
    .JoinQueryOver(() => pair.Notification, () => notification)
    // here is the filter
    .Where(() => !notification.IsRead)
    // now the trick to take only related to our user
    .Where(() => pair.User.Id == user.Id)
    // and get the user Id
    .Select(x => pair.User.Id);

var listOfUsers = session.QueryOver<User>(() => user)
    .WithSubquery
        .WhereProperty(() => user.Id)
        .In(subquery)
    // paging
    .Take(10)
    .Skip(10)
    .List<User>();

为每个 userId 查找 5 个未读通知

var userId = 1;
var subqueryByUser = QueryOver.Of<UserNotification>(() => pair)
    // now we do not need any kind of a join 
    // just have to filter these pairs related to user
    .Where(() => pair.User.Id == userId)
    // and get the notification Id
    .Select(x => pair.Notification.Id);

var notificationsPerUser = session.QueryOver<Notification>(() => notification)
    .WithSubquery
        .WhereProperty(() => notification.Id)
        .In(subqueryByUser)
    .Where(() => !notification.IsRead)
    // if needed we can order
    // .OrderBy(...
    .Take(5)
    .List<Notification>()

Answer 2

session.Get<TEntity>(entityId) 可以让我们加载 AS IS 映射的实体。这就是合同。

如果我们想获得过滤结果，我们必须使用另一个合约来接收数据：Session.CreateCriteria()（或任何其他查询 API，即QueryOver()）

因此，在我们的例子中，我们应该构建查询以查找具有未读通知的用户：

Occupation Notification= null;
User user = null;

var subquery = QueryOver.Of<Notification>(() => notification) 
    .Where(() => !notification.IsRead )
    // just related to the user, from outer query
    .Where(() => notification.User.ID == user.ID)
    .Select(x => notification.User.ID);

var list = session.QueryOver<User>(() => user)
    .WithSubquery
        .WhereProperty(() => user.ID)
        .In(subquery)
    // paging
    .Take(10)
    .Skip(10)
    .List<User>();

我们在这里可以看到，期望（实际上是必须的）通知回溯到它的父级和用户：

public class Notification
{
    ...
    public User User {get;set;}
}

但这不应该是一个问题，它只是一个映射，而不是数据库中的变化

类似的查询（在 Notification 之上），我们只能获取其中的前 5 个：

var notifications = session.QueryOver<Notification>(() => notification)
    // here is a userId for a specific user.
    // we can use IN() to load for more of them
    .Where(() => notification.User.ID != userId)
    .Take(5)
    .List<Notification>()
;