EF 4.1 - 将项目添加到虚拟的集合属性中

发布于 2024-11-02 17:49:53 字数 655 浏览 0 评论 0原文

我首先使用 EF 4.1 代码。给出以下类片段：

public class Doctor
{
    public virtual ICollection<Hospital> Hospitals { get; set; }
}

注意：我在数据库上下文中有这个：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    this.Configuration.LazyLoadingEnabled = false;
}

我想确保这里不涉及延迟加载。

我遇到的问题是，如果 Hospitals 属性上没有 virtual 关键字，当我检索一位确实有与其关联的医院的医生时，该集合为空。通过包含 virtual 关键字，hospitals 集合确实包含 1 个项目，这正是我所期望的。

问题是，当我想创建一个全新的医生并立即将他与医院关联时，我会得到一个 Null reference 异常，因为 Hospitals 属性尚未初始化。

有人可以指出我在这里做错了什么吗？创建新医生时如何向医院添加项目。

干杯。贾斯。

原文

I'm using EF 4.1 code first. Given the following class snippet:

public class Doctor
{
    public virtual ICollection<Hospital> Hospitals { get; set; }
}

Note: I have this in the database context:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    this.Configuration.LazyLoadingEnabled = false;
}

I wanted to make sure that lazy loading is not involved here.

The issue I have is that, without the virtual keyword on the Hospitals property, when I retrieve a doctor that does have a hospital associated with him, the collection is empty.
By including the virtual keyword, the hospitals collection does contain 1 item, which is what I expect.

The problem is that, when I want to create a brand new doctor and associate him with a hospital immediately, I get a Null reference exception, since the Hospitals property has not been initialised yet.

Can someone point out what I'm doing wrong here? How can I add items to the Hospitals upon creating a new doctor.

Cheers.
Jas.

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萌逼全场 2024-11-09 17:49:53

您的代码与您通常在所有示例中看到的代码相同，但为了使这项工作正常进行，此代码要好得多：

public class Doctor
{
    private ICollection<Hospital> _hospitals;
    public virtual ICollection<Hospital> Hospitals 
    { 
        get { return _hospitals ?? (_hospitals = new HashSet<Hospital>()); }
        set { _hospitals = value } 
    }
}

如果您不使用 virtual 关键字，EF 将不会为您初始化集合。同时，如果您通过其构造函数创建全新的Doctor，则必须自己处理初始化。

Your code is something what you usually see in all examples but to make this work this one is much better:

public class Doctor
{
    private ICollection<Hospital> _hospitals;
    public virtual ICollection<Hospital> Hospitals 
    { 
        get { return _hospitals ?? (_hospitals = new HashSet<Hospital>()); }
        set { _hospitals = value } 
    }
}

If you don't use virtual keyword EF will not initialize collection for you. In the same time if you create brand new Doctor via its constructor you must handle initialization yourselves.

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倾城月光淡如水﹏ 2024-11-09 17:49:53

我想这可以帮助你。

public class Doctor
{
    public Doctor()
    {
       Hospitals = new ICollection<Hospital>();
    }

    public virtual ICollection<Hospital> Hospitals { get; set; }
}

I think this can help you.

public class Doctor
{
    public Doctor()
    {
       Hospitals = new ICollection<Hospital>();
    }

    public virtual ICollection<Hospital> Hospitals { get; set; }
}

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