实体框架只读集合

Question

考虑一个客户,公司,员工等具有ContactInfo属性的域,该属性又包含一组地址,电话,电子邮件等等......

这是我的缩写ContactInfo:

public class ContactInfo : Entity<int>
{
    public ContactInfo()
    {
        Addresses = new HashSet<Address>();          
    }

    public virtual ISet<Address> Addresses { get ; private set; }

    public Address PrimaryAddress
    {
        get { return Addresses.FirstOrDefault(a => a.IsPrimary); }
    }

    public bool AddAddress(Address address)
    {
        // insure there is only one primary address in collection
        if (address.IsPrimary)
        {                  
            if (PrimaryAddress != null)
            {
                PrimaryAddress.IsPrimary = false;
            }
        }
        else
        {
            // make sure the only address in collection is primary
            if (!Addresses.Any())
            {
                address.IsPrimary = true;
            }
        }
        return Addresses.Add(address);
    }
}

一些注释(我不是100%确定这些是EF"最佳实践"):

• Address(es)的集合是虚拟的,允许延迟加载
• 私人二手收集器禁止收集更换
• 集合是ISet为了确保每个联系人没有重复的地址
• 使用AddAddress方法我可以确保总有最多1个主要地址....

我希望(如果可能的话)阻止通过ContactInfo.Addresses.Add()方法添加地址并强制使用ContactInfo.AddAddress(Address address)...

我正在考虑通过实现这一组地址,ReadOnlyCollection但这是否适用于实体框架(v5)？

我该怎么做？

Answer 1

Edo van Asseldonk建议的另一个选项是创建一个从Collection继承其行为的自定义集合.

您必须为ISet制作自己的实现,但原理是相同的.

通过隐藏任何修改列表并将其标记为过时的方法,您可以有效地获得ReadOnlyCollection,但是当它取消装箱为Collection时,EF仍然可以修改它.在我的版本中,我为List添加了一个隐式运算符转换,因此我们不必在添加项时取消收集集合:

var list = ListProperty.ToList();
list.Add(entity)
ListProperty = list;

哪里

public virtual EntityCollection<MyEntity> ListProperty { get; protected set; }

这是EntityCollection:

public class EntityCollection<T> : Collection<T>
{
    [Obsolete("Unboxing this collection is only allowed in the declarating class.", true)]
    public new void Add(T item) { }

    [Obsolete("Unboxing this collection is only allowed in the declarating class.", true)]
    public new void Clear() { }

    [Obsolete("Unboxing this collection is only allowed in the declarating class.", true)]
    public new void Insert(int index, T item) { }

    [Obsolete("Unboxing this collection is only allowed in the declarating class.", true)]
    public new void Remove(T item) { }

    [Obsolete("Unboxing this collection is only allowed in the declarating class.", true)]
    public new void RemoveAt(int index) { }

    public static implicit operator EntityCollection<T>(List<T> source)
    {
        var target = new EntityCollection<T>();
        foreach (var item in source)
            ((Collection<T>) target).Add(item); // unbox

        return target;
    }
}

这样您仍然可以像往常一样运行Linq,但在尝试修改Collection属性时会得到正确的使用警告.将它解压缩到集合将是唯一的方法:

((Collection<MyEntity>)ListProperty).Add(entity);

Answer 2

一种方法是保护 ICollection 属性并创建 IEnumerable 的新属性，该属性仅返回 ICollection 属性的列表。

这样做的缺点是您无法通过 ContactInfo 查询地址，例如获取居住在该城市的所有联系信息。

这不可能！：

from c in ContactInfos 
where c.Addresses.Contains(x => x.City == "New York") 
select c

代码：

public class ContactInfo : Entity<int>
{
    public ContactInfo()
    {
        Addresses = new HashSet<Address>();          
    }

    protected virtual ISet<Address> AddressesCollection { get ; private set; }

    public IEnumerable<Address> Addresses { get { return AddressesCollection; }}

    public Address PrimaryAddress
    {
        get { return Addresses.FirstOrDefault(a => a.IsPrimary); }
    }

    public bool AddAddress(Address address)
    {
        // insure there is only one primary address in collection
        if (address.IsPrimary)
        {                  
            if (PrimaryAddress != null)
            {
                PrimaryAddress.IsPrimary = false;
            }
        }
        else
        {
            // make sure the only address in collection is primary
            if (!Addresses.Any())
            {
                address.IsPrimary = true;
            }
        }
        return Addresses.Add(address);
    }
}