实体框架在“过度应用”后失去了对导航属性的跟踪

Question

我有一个像 Person 这样的模型，它可以住在 Street，而 Street 在 City ，而 City 又在 Country。还有一些 ActivityRecords 供一些 Persons 使用。

public class Country
{
    [Key]
    public int id { get; set; }
    public string name { get; set; }
}
public class City
{
    [Key]
    public int id { get; set; }
    public string name { get; set; }

    [ForeignKey("Country")]
    public int country_id { get; set; }
    public virtual Country Country { get; set; }
}
public class Street
{
    [Key]
    public int id { get; set; }
    public string name { get; set; }

    [ForeignKey("City")]
    public int city_id { get; set; }
    public virtual City City { get; set; }
}

public class Person
{
    [Key]
    public int id { get; set; }

    ForeignKey("Street")]
    public int? street_id { get; set; }
    public virtual Street Street { get; set; }

    //no connection to ActivityRecord[]
}

public class ActivityRecord
{
    [Key]
    public int id { get; set; }
    public string desc { get; set; }

    [ForeignKey("Person")]
    public int? person_id { get; set; }
    public virtual Person Person { get; set; }
}

我需要列出部分人员信息，包括他们在国家/地区的地址以及其中一项活动（如果有的话）（否则为空）。为了简化示例，我特意删除了所有细节和列。

所以，我在我的代码中提到了这一点：

context.Persons.AsNoTracking().OrderBy(p => p.id).Skip(0).Take(10).GroupJoin(
    context.ActivityRecords,
    p => p.id,
    ar => ar.person_id,
    (p, ar) => new { p = p, ar = ar.FirstOrDefault() } //join 1 or 0 entries
).Select(result => new
{
    id = result.t.id,
    street = result.t.Street.name,
    city = result.t.Street.City.name,
    country = result.t.Street.City.Country.name
}).ToArray();

当我检查 EF 生成的查询时，我在同一个表上多次看到左外连接（街道、城市）：

SELECT 
    [Limit1].[id] AS [id], 
    [Extent3].[name] AS [name], 
    [Extent5].[name] AS [name1], 
    [Extent8].[name] AS [name2]
    FROM         (SELECT TOP (10) [Extent1].[id] AS [id], [Extent1].[street_id] AS [street_id]
        FROM ( SELECT [Extent1].[id] AS [id], [Extent1].[street_id] AS [street_id], row_number() OVER (ORDER BY [Extent1].[id] ASC) AS [row_number]
            FROM [dbo].[Persons] AS [Extent1]
        )  AS [Extent1]
        WHERE [Extent1].[row_number] > 0
        ORDER BY [Extent1].[id] ASC ) AS [Limit1]
    OUTER APPLY  (SELECT TOP (1) [Extent2].[id] AS [id]
        FROM [dbo].[ActivityRecords] AS [Extent2]
        WHERE [Limit1].[id] = [Extent2].[person_id] ) AS [Limit2]
    LEFT OUTER JOIN [dbo].[Streets] AS [Extent3]
            ON [Limit1].[street_id] = [Extent3].[id]
    LEFT OUTER JOIN [dbo].[Streets] AS [Extent4]  /* <-- Seriously? */
            ON [Limit1].[street_id] = [Extent4].[id]
    LEFT OUTER JOIN [dbo].[Cities] AS [Extent5]
            ON [Extent4].[city_id] = [Extent5].[id]
    LEFT OUTER JOIN [dbo].[Streets] AS [Extent6] /* <-- Come on! */
            ON [Limit1].[street_id] = [Extent6].[id]
    LEFT OUTER JOIN [dbo].[Cities] AS [Extent7] /* <-- Hey! */
            ON [Extent6].[city_id] = [Extent7].[id]
    LEFT OUTER JOIN [dbo].[Countries] AS [Extent8]
            ON [Extent7].[country_id] = [Extent8].[id]

当我只删除组加入中的单行连接时

...(p, ar) => 新 { p = p, ar = ar } ...

它工作正常，每个表连接一次。

我尝试在 join 之前包含表，但没有成功。唯一可行的方法是在 join 之前选择所有 person-streets-cities，但问题是它会在 之前 加载所有这些记录strong> 削减 TOP 10，实际上我有很多繁重的计算列（当问题仍然可见时，如果删除 Skip() 和 Take()，这个查询会简单得多，但将 GroupJoin() 留给 FirstOrDefault())。

所以，我的问题是：如何通知 EF 不要多次包含相同的表，是否有解决方法？为什么单行连接后导航属性链开始丢失？

Answer 1

这确实是 EF 查询编译中的一个错误，因此从 EF 6.1.1 升级到 EF 6.1.2 解决了这个问题。