是否有可能插入/更新前执行POCO行动？ [英] Is it possible perform actions in POCO before insert/update?

问题描述

让我们假设这个实体框架示例：

Let's assume this Entity Framework sample:

public class User
{ 
    public int UserID { get; set; } 
    public string Name { get; set; }      
} 

public class MyDbContext : DbContext 
{ 
    public DbSet<User> Users { get; set; } 
} 

class Program 
{ 
    static void Main(string[] args) 
    { 
        using (var db = new MyDbContext ()) 
        {     
            var user = new User { Name = "Foo"}; 
            db.Users.Add(user); 
            db.SaveChanges();      

            Console.WriteLine("Press any key to exit..."); 
            Console.ReadKey(); 
        } 
    } 
}

我要添加到<强>用户类的事件，如BeforeInsert或更新前，而当代码...

I want add to User class events, like "BeforeInsert" or "BeforeUpdate", and when the code...

db.Users.Add(user); 

...是任何地方的应用程序执行时，BeforeInsert的方法将得到提升。是否可以？

... is executed anywhere in the application, the "BeforeInsert" method will be raised. Is it possible?

推荐答案

@ JC的答案是正确的。我将只显示代码，在其中你可以做你想做的。首先，覆盖SaveChanges方法在上下文，并调用这个被覆盖的SaveChanges方法： context.SaveChanges（真）代替的 conntext.SaveChanges（）的

@JC's answer is correct. I will just show code, in which you can do what you want. First of all, override SaveChanges method in your context, and call this overriden SaveChanges method: context.SaveChanges(true) instead of conntext.SaveChanges()

public class MyDbContext : DbContext 
{ 
    public DbSet<User> Users { get; set; } 

    public int SaveChanges(bool performCustomOperations)
    {
        if(performCustomOperations)
        {
            CustomContextManager contextManager = new CustomContextManager(this);
            //Perform operations you want before saving data
            contextManager.PerformBeforeUpdate();

            //To do: Add your own PerformBeforeInsert method to CustomContextManager class
        }

        //Save changes to underlying database
        this.SaveChanges();
    }
} 

您CustomContextManager类应该是这样的。在 PerformBeforeUpdate 方式执行您之前更新操作。您可以添加自己的 PerformBeforeInsert和/或PerformBeforeDelete 的方法。

Your CustomContextManager class should look like this. Performing your before update operations in PerformBeforeUpdate method. You can add your own PerformBeforeInsert and/or PerformBeforeDelete methods.

public class CustomContextManager
{
    private MyDbContext context;

    public CustomContextManager(MyDbContext contextParam)
    {
        if (contextParam == null)
            throw new ArgumentNUllException(nameof(contextParam));

        this.context = contextParam;
    }

    public void PerformBeforeUpdate
    {
        //Get object context to be able to perform operations
        System.Data.Objects.ObjectContext myObjectContext =
            ((IObjectContextAdapter)context).ObjectContext;

        IEnumerable<ObjectStateEntry> updatedRecords =
            taxesObjectContext.ObjectStateManager.GetObjectStateEntries(
            System.Data.EntityState.Modified);

        if (updatedRecords != null
            && updatedRecords.Count() > 0)
        {
            foreach (ObjectStateEntry stateEntry in updatedRecords)
            {
                if (stateEntry != null
                    && stateEntry.Entity != null)
                {
                    //Do what operations you want instead of below linnes
                    User modifiedUser = stateEntry.Entity as User;
                    if(modifiedUser != null)
                        modifiedUser.Name = "Altered before update";
                }
            }
        }
    }
}

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