EF：加载相关实体惰性方式不起作用

debugcn 发表于 Dev

艳丽的

我哪里错了？我收到NullReferenceExeption了Navigation属性Events。它被标记为virtual，LazyLoadingEnabled并被明确允许。

程序代码：

using (var db = new Db())
{
    var person = new Person();
    person.Name = "bla bla";
    db.Persons.Add(person);
    person.Events = new List<Event>(1);
    person.Events.Add(new Event() { Description = "ABC", At = DateTime.Now });
    db.SaveChanges();
}

using (var db = new Db())
{
    var person = db.Persons.First();

    Console.WriteLine(person.Events == null);  //Output: True
    Console.WriteLine(person.Events.Count);    //System.NullReferenceException
}

显式加载工作：

var person = db.Persons.First();
db.Entry(person).Collection(p => p.Events).Load();
Console.WriteLine(person.Events == null);  //Output: False
Console.WriteLine(person.Events.Count);    //1

类结构：

class Db : DbContext
{
    public Db()
    {
        Database.SetInitializer(new DropCreateDatabaseAlways<Db>());
        Configuration.LazyLoadingEnabled = true;
    }

    public DbSet<Person> Persons { get; set; }
    public DbSet<Event> Events { get; set; }
}

class Person
{
    public int id { get; set; }
    public string Name { get; set; }

    public virtual List<Event> Events { get; set; }
}

class Event
{
    public int id { get; set; }
    public DateTime At { get; set; }
    public string Description { get; set; }

    public Person Person { get; set; }
    public int PersonId { get; set; }
}

理查德

您的模型类需要是公共的才能延迟加载。更改为class Personand class Eventbe public class Personetc，然后您的测试程序将开始工作。

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