查询具有最低级别过滤器的多级实体

Question

所以我有 3 个实体类:

public partial class Event
{
    public Event()
    {
        Recurrences = new HashSet<Recurrence>();
    }
    public int Id { get; set; }
    public ICollection<Recurrence> Recurrences { get; set; }
}

public partial class Recurrence
{
    public Recurrence()
    {
        AspNetUsers = new HashSet<AspNetUser>();
    }
    public int Id { get; set; }
    public int EventId { get; set; }
    public ICollection<AspNetUser> AspNetUsers { get; set; }
}

public partial class AspNetUser
{
    public AspNetUser()
    {
        Recurrences = new HashSet<Recurrence>();
    }
    public string Id { get; set; }
    public string UserName { get; set; }
    public ICollection<Recurrence> Recurrences { get; set; }
}

我想在给定 aspnetuser.id 的情况下使用行到实体来获取事件。到目前为止，这是我所拥有的，但它返回了一个错误：

// GET: api/Events?userId={userId}
    public IQueryable<Event> GetEvents(string userId)
    {
        return db.Events
             .Include(e => e.Recurrences
                .Select(u => u.AspNetUsers.Where(i => i.Id == userId)));
    }

当我排除 where 子句时它工作正常。请帮忙。提前致谢！

Answer 1

我认为 Include() 的含义与您认为的不同。 (https://msdn.microsoft.com/en-us/library/bb738708%28v=vs.110%29.aspx) What it does is tell the db set to be sure to bring in relationships for that object. By default (last I checked), the db context will auto pull in all relationships, so this isn't necessary. However, if you've turned off the lazy-loading (http://www.entityframeworktutorial.net/EntityFramework4.3/lazy-loading-with-dbcontext.aspx) 然后你需要 .Include() 所有你想在查询中拥有的关系。

这应该可以解决您的问题。不过，我不保证生成的 SQL 不会很傻。

如果您打开了延迟加载：

db.Events.Include("Recurrences").Include("Recurrences.AspNetUsers")
  .Where(e => e.Recurrences
    .Any(r => r.AspNetUsers
      .Any(u => u.Id ==userId)));

如果您关闭了延迟加载：

db.Events
  .Where(e => e.Recurrences
    .Any(r => r.AspNetUsers
      .Any(u => u.Id ==userId)));

此外，如果您无法看到错误，您可以在返回之前对查询进行 .ToList() 处理，这样它就会在您的代码中失败，而不是深入到 Web API 堆栈中。就个人而言，我喜欢这样做，这样我就可以 try/catch 查询并正确处理它。

查询具有最低级别过滤器的多级实体

query multi-level entity with filter at the lowest level

c#

asp.net

asp.net-web-api

linq-to-entities