c# - 首先使用实体​​框架代码和 IOC 容器来创建没有默认构造函数的实体

Question

我想构建一个加密其某些属性的 Entity Framework 代码优先数据层。为此，在使用从数据库加载的数据创建实例时，应该注入(inject) ICryptographer。

是否可以使用像 unity 这样的 IOC 容器注入(inject) ICryptographer？

DAL 示例:

public class context : DbContext
{
    public DbSet<Credentials> Credentials {get;set;}
}

public CredentialsConfiguration()
{
    ToTable("Profiles");
    HasKey(p => p.ProfileName);
    Ignore(p => p.SecretKey);
    Ignore(p => p.AccessKey);
    Property(p => p._accessKey)
        .HasColumnName("AccessKey");
    Property(p => p._secretKey)
        .HasColumnName("SecretKey");
}

通用实体程序集:(内部结构对 DAL 可见)

public class Credentials
{
    private readonly ICryptographer _cryptographer;

    public Credentials(ICryptographer cryptographer)
    {
        _cryptographer = cryptographer;
    }


    internal string _accessKey { get; set; }
    public string AccessKey
    {
        get { return _cryptographer.Decrypt(_accessKey); }
        set { _accessKey = _cryptographer.Encrypt(value); }
    }

}

Answer 1

这是一个非常人为的例子，但可能会把你推向正确的方向

我们需要一种方法来知道何时将属性注入(inject)实体类，因为它们被标记为使用

public interface ICryptographerUser {
    ICryptographer Cryptographer { get; set; }
}

ICryptographer 定义为

public interface ICryptographer {
    string Decrypt(string value);
    string Encrypt(string value);
}

将被注入(inject)的实例定义为

public class Cryptographer : ICryptographer {
    public string Decrypt(string value) {
        return "Decrypted";
    }

    public string Encrypt(string value) {
        return "Encrypted";
    }
}

当添加一个实体时，我们需要使用一个Factory，它知道我们需要注入(inject)属性(您可以使用 IOC 来做到这一点)

public static class EntityFactory {
    public static T CreateInstance<T> () {
        var entity = Activator.CreateInstance<T>();
        if (entity is ICryptographerUser) {
            //INJECT INSTANCE HERE
            (entity as ICryptographerUser).Cryptographer = new Cryptographer();
        }

        return entity;
    }      
}

现在添加我们可以使用的实体

var entity = EntityFactory.CreateInstance<Credentials>();
        entity.SetAccessKey("123");
        entity.SecretKey = "456";
        entity.ProfileName = "a";

        contect.Set<Credentials>().Add(entity);

当从 Context 查询对象时，以下代码将注入(inject)对象，但这是在它们各自的属性已经设置之后完成的

public MyContext() {
        IObjectContextAdapter objectContextAdapter = (this as IObjectContextAdapter);
        objectContextAdapter.ObjectContext.ObjectStateManager.ObjectStateManagerChanged += ObjectStateManager_ObjectStateManagerChanged;
    }

    private void ObjectStateManager_ObjectStateManagerChanged(object sender, System.ComponentModel.CollectionChangeEventArgs e) {
        // we are only interested in entities that
        // have been added to the state manager
        if (e.Action != CollectionChangeAction.Add)
            return;

        IObjectContextAdapter objectContextAdapter = (this as IObjectContextAdapter);

        var state = objectContextAdapter.ObjectContext.ObjectStateManager.GetObjectStateEntry(e.Element).State;

        // we are only interested in entities that
        // are unchanged (that is; loaded from DB)
        if (state != EntityState.Unchanged)
            return;

        OnObjectMaterialized(e.Element);
    }

    private void OnObjectMaterialized(object e) {
        if (e is ICryptographerUser) {
            //INJECT INSTANCE HERE
            (e as ICryptographerUser).Cryptographer = new Cryptographer();
        }      
    }

因为实例只会在 Entity 被具体化后注入(inject)，所以我需要修改你的 Entity 定义如下

public class Credentials : ICryptographerUser {
    public string ProfileName { get; set; }

    internal string _secretKey { get; set; }
    internal string _accessKey { get; set; }


    public string SecretKey { get; set; }

    public string AccessKey {
        get { return _accessKey; }
        private set { _accessKey = value; }
    }

    public string AccessKeyDecrypted {
        get { return Cryptographer.Decrypt(_accessKey); }
    }

    public void SetAccessKey(string value) {
        _accessKey = Cryptographer.Encrypt(value);
    }

    public ICryptographer Cryptographer { get; set; }
}

请注意 AccessKey 具有 private set { _accessKey = value; } 允许 EF 在 object 实现时设置属性，但是当您设置属性值时，您必须调用 public void SetAccessKey(string value) 使用 Cryptographer 来加密字段。