实体框架代码优先的IQueryable [英] Entity Framework Code First IQueryable

问题描述

我正在使用Entity Framework Code First，但遇到了一个小障碍.我有一个这样定义的人"类:

I am using Entity Framework Code First and ran into a small road block. I have a class "Person" defined as such:

public class Person
{
    public Guid Id { get; set; }
    public virtual ICollection<History> History { get; set; }
}

以及这样定义的历史"类:

and a class "History" defined as such:

public class History
{
    public Guid Id { get; set; }
    public virtual Person Owner { get; set; }
    public DateTime OnDate { get; set; }
}

但是，当我打电话时:

IEnumerable<History> results = person.History
                               .OrderBy(h => h.OnDate)
                               .Take(50)
                               .ToArray();

似乎会拉取该人的所有历史记录，然后在内存中对其进行排序.关于我所缺少的内容有什么建议吗?

It appears to pull all of the history for the person, then order it and such in memory. Any recommendations on what I'm missing?

提前谢谢！

推荐答案

因为您要查询EF给出的IEnumerable(即LINQ到对象)而不是IQueryable(即LINQ到实体).

Because you are querying an IEnumerable (ie: LINQ to Objects) not IQueryable (ie: LINQ to Entities) given by EF.

您应该使用

IEnumerable<History> results = context.History.Where(h => h.Person.Id = "sfssd").OrderBy(h => h.OnDate).Take(50)

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