检查导航属性是否加载 [英] Check if navigational property is loaded

问题描述

是否可以检查是否已加载导航属性？当我尝试访问它时，我只得到一个 ObjectDisposedException

Is it possible to check if a navigational property has been loaded? When I try to access it I only get an ObjectDisposedException

ObjectContext实例被处理，不能再用于需要连接的操作。

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

public class Factory {
    // ..
    public virtual ICollection<Machine> Machines { get; set; }
}

// ...
IList<Factory> set;
using (MyContext context = new MyContext()) {
    set = context.Factories.ToList();
}

... later on

// Is it possible to check if .Machines is loaded here?
if (set.First().Machines == Loaded)

    // Let's open a new context and load it then
}

搜索这个问题的解决方案是使用 Include（）包括机器在第一次运行，但我想避免加载它，直到必要的。我也尝试使用（...）{} 新的框，但我仍然得到例外。

我也想避免附加，因为构建大型对象图时速度非常慢。

The solution I have found when searching for this is to use Include() and just include the machines in the first run, but I would like to avoid loading it until neccessary. I also tried to box it in a new using(...){} but I still get the exception.
I'd also like to avoid Attach since it is extremely slow when building large object graphs.

我想我可以使用 bool IsMachinesLoaded 或某事，但我认为应该有一些方法来检查它没有..

I guess I could use a bool IsMachinesLoaded or something, but I figured there ought to be some way to check it without that..

推荐答案

我用一个方法解决了：

protected bool IsLoaded<TEntity>(TEntity entity, Func<TEntity, object> testAction)
{
    try
    {
        testAction(entity);
        return true;
    }
    catch (ObjectDisposedException)
    {
        return false;
    }
}

通过以下方式调用：

if (IsLoaded(myEntity, entity => entity.MyList)){
    // the navigational property exists and can be accesses
}

这篇关于检查导航属性是否加载的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！