在Entity框架中,如何在保存之前调用Entity上的方法

Question

下面我创建了一个演示实体来演示我正在寻找的东西:

public class User :  IValidatableObject
{
    public string Name { get; set; }

    [Required]
    public DateTime CreationDate { get; set; }

    public DateTime UpdatedOnDate { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if(Name = "abc")
        {
            yield return new ValidationResult("please choose any other name then abc", new[] { "Name" });
        }
    }
}

我正在实现IValidatableObject接口来使这个实体SelfValidating.

现在正在创建新的用户iam这样做

User u = new User();
u.Name = "Some name";
u.CreationDate = DateTime.Now
dbContext.Users.Add(u);
dbContext.SaveChanges();

我打算u.CreationDate=DateTime.Now;在User课堂内转移代码.并实现一个接口,该接口提供将在保存之前和验证之后执行的方法

// class structure that I am looking for
public class User : IValidatableObject,IMyCustomInterFace
{
    //rest codes as above class

    public void MyMethod(Whatever)
    {
        //this method gets called after Validate() and before save

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Added)
        {
            //add creation date_time
            this.CreationDate=DateTime.Now;

            //SET MORE DEFAULTS
        }

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Modified)
        {
            //update Updation time
            this.UpdatedOnDate = DateTime.Now;
        }
    }
}

现在要创建一个新用户,我只需要做如下所示,注意我这次没有添加date属性,Class自动完成.

User u = new User();
u.Name = "Some name";
dbContext.Users.Add(u);
dbContext.SaveChanges();

要更新用户,UpdatedOnDate属性将按类自动更新

User u = getUserFromSomeWhere();
u.Name = "Updated Name";
dataContext.Entry<User>(u).State = System.Data.EntityState.Modified;
dbContext.SaveChanges();

我的问题:是否有任何现有的接口,它提供了一些方法,该方法被调用之前Save和AfterValidate或做这一点,我可能不会知道的其他一些方法.

或者,如果我创建自定义界面,我如何使其方法按我想要的顺序执行.

Answer 1

我有一个几乎相同的情况,我通过处理上下文中的SavingChanges事件来管理它.

首先,我创建一个定义时间戳操作的接口:

public interface IHasTimeStamp
{
    void DoTimeStamp();
}

然后我在我的实体中实现这个接口:

Public class User : IHasTimeStamp
(
    public void DoTimeStamp()
    {
        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Added)        
        {            
            //add creation date_time            
            this.CreationDate=DateTime.Now;            
        }        

        if(dataContext.Entry<User>(this).State == System.Data.EntityState.Modified)        
        {            
            //update Updation time            
            this.UpdatedOnDate=DateTime.Now;        
        }
    }
}

最后一步是注册SavingChanges处理程序并实现它.

public partial class MyEntities
{
    partial void OnContextCreated()
    {
        // Register the handler for the SavingChanges event.
        this.SavingChanges
            += new EventHandler(context_SavingChanges);
    }

    // SavingChanges event handler.
    private static void context_SavingChanges(object sender, EventArgs e)
    {
        // Validate the state of each entity in the context
        // before SaveChanges can succeed.
        foreach (ObjectStateEntry entry in
            ((ObjectContext)sender).ObjectStateManager.GetObjectStateEntries(EntityState.Added | EntityState.Modified))
        {
            if (!entry.IsRelationship && (entry.Entity is IHasTimeStamp))
            {
                (entry.Entity as IHasTimeStamp).DoTimeStamp();
            }
        }
    }
}