在存储库模式的纯POCO实体更新问题 [英] Pure POCO entity update problem in repository pattern

问题描述

我在UserRepository一个问题，我想更新的用户。我不希望某些字段更新，如密码，除非另有说明。例如，当我从视图中传递用户，该服务存储库，它发出了一个空或空密码字符串的用户。此空被写入数据库（我不想）。

I have a problem in my UserRepository in which I want to update a user. I dont want certain fields updated, such as password, unless specified. For example, When I pass the User from the view, to the service to the repository, it sends up the user with a null or empty password string. This null gets written to the database (which I dont want).

如何处理的情况也是这样吗？

How do I handle a situation like this?

域

public class User
{
    public int UserId { get; set; }

    public string Email { get; set; }
    public string Password { get; set; }
}

库

    public User Save(User user)
    {
        if (user.UserId > 0)
        {
            User dbUser = context.Users.FirstOrDefault(u => u.UserId == user.UserId);
            //What do I do here?
        }
        context.Users.AddObject(user);
        context.SaveChanges();
        return user;
    }

比方说，在这种情况下，我的看法让我改变仅电子邮件，所以被送回保存的唯一的事（） 方法是： user.UserId 和 user.Email ，而 user.password的为空。在我的情况下，数据库将引发错误，因为密码应为空。

Lets say in this case, my view allows me to change only Email, so the only thing that gets sent back to the Save() method are: user.UserId and user.Email while user.Password is null. In my case, the database throws error because Password should be nullable.

推荐答案

独立POCO方案（你会不会从数据库更新之前加载用户）：

您可以选择性地说哪些属性必须进行更新：

You can selectively say which properties must be updated:

public User Save(User user)     
{         
    if (user.UserId == 0)         
    {             
        context.Users.AddObject(user);         
    }
    else
    {
        context.Users.Attach(user);
        ObjectStateEntry entry = context.ObjectStateManager.GetObjectStateEntry(user);
        entry.SetModifiedProperty("Email");
    }

    context.SaveChanges();         
    return user;     
}

您还可以创建你两个重载保存方法。首先将更新整个对象，第二个将只更新明确选择属性：

You can also create two overloads of you Save method. First will update whole object, second will update only explicitly selected properties:

public User Save(User user)     
{         
    if (user.UserId == 0)         
    {             
        context.Users.AddObject(user);         
    }
    else
    {
        context.Users.Attach(user);
        context.ObjectStateManager.ChangeObjectState(user, EntityState.Modified);        
    }

    context.SaveChanges();         
    return user;     
}

public User Save(User user, IEnumerable<Expression<Func<User, object>>> properties)     
{         
    if (user.UserId == 0)         
    {             
        context.Users.AddObject(user);         
    }
    else
    {
        context.Users.Attach(user);
        ObjectStateEntry entry = context.ObjectStateManager.GetObjectStateEntry(user);
        foreach(var selector in properties)
        {
            string propertyName = PropertyToString(selector.Body);
            entry.SetModifiedProperty(propertyName);
        }
    }

    context.SaveChanges();         
    return user;     
}

// Doesn't work for navigation properties!
private static string PropertyToString(Expression selector)
{
    if (selector.NodeType == ExpressionType.MemberAccess)
    {
        return ((selector as MemberExpression).Member as PropertyInfo).Name;
    }

    throw new InvalidOperationException();
}

您将调用第二个重载是这样的：

You will call the second overload this way:

userRepository.Save(user, new List<Expression<Func<User, object>>> 
    { 
        u => u.Email 
    });

连接方案（你会从数据库更新之前加载用户）：

您可以修改您的保存方法，接受委托，这样就可以控制更新将如何进行：

You can modify your Save method to accept delegate so that you can control how update will be performed:

public User Save(User user, Action<User, User> updateStrategy)                                
{                                  
    if (user.UserId > 0)                                  
    {
        User dbUser = context.Users.FirstOrDefault(u => u.UserId == user.UserId);
        updateStrategy(dbUser, user);                                                                        
    }        
    else
    {                          
        // New object - all properties should be saved
        context.Users.AddObject(user);
    }

    context.SaveChanges();                                  
    return user;                              
}  

您会调用该方法是这样的：

You will call the method this way:

var user = GetUpdatedUserFromSomewhere();
repository.Save(user, (dbUser, mergedUser) => 
    {
        dbUser.Email = mergedUser.Email;
    });

总之，尽管我的例子你一定要想想达林的职位和特殊ModelViews进行更新。

Anyway, despite of my examples you should definitely think about Darin's post and special ModelViews for updating.

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