asp.net-mvc - Is there an equivalent of Rails ActiveRecord::Callbacks in ASP MVC?

Question

Is there an equivalent of Rails ActiveRecord::Callbacks in ASP MVC?

http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html

I'm in a situation where we are not using identities for our primary key. We do this for reasons specific to our DB sharding design. Because of this we have a lookup table to find the next ID for a specific table. I'd like to automatically get this value and set it in an abstract class whenever a model is created/updated and before it is saved. I also need to update the lookup table with an incremented 'nextID' after the save is successful.

I'm open to other solutions on how to do this without callbacks as well.

Answer 1

所以你需要回调来增加查找表中的 ID 吗？AFAIK 在 ASP.NET 中没有等效项，您可以尝试使用异步控制器（http://msdn.microsoft.com/en-us/library/ee728598%28v=vs.100%29.aspx）并等待成功保存后的状态更改，但我更喜欢使用专门为此服务的服务，例如 Snowflake ( https://github.com/twitter/snowflake/ )。

Answer 2

我找到了一个使用覆盖而不是回调的解决方案。我希望 ASP mvc 随着框架的不断成熟增加对回调的支持，因为回调通过允许 OnSave 事件存在于事件所关注的模型中而不是集中式 DbContext 类（分离担忧）。

解决方案：

SaveChanges 方法可以在 Context 类中被覆盖（Entity Framework Power Tools创建 Context 类是 'Models' 目录）。

    public override int SaveChanges()
    {
        // create a cache for id values in case their are multiple added entries in the dbcontext for the same entitytype
        Dictionary<string, UniqueID> idCache = new Dictionary<string, UniqueID>();
        IEnumerable<DbEntityEntry> changes = this.ChangeTracker.Entries();
        foreach (var entry in changes)
        {
            //check if this is a new row (do nothing if its only a row update because there is no id change)
            if (entry.State == System.Data.EntityState.Added)
            {
                //determine the table name and ID field (by convention)
                string tableName = entry.Entity.GetType().Name;
                string idField = entry.Entity.GetType().Name + "ID";
                UniqueID id = null;
                //if we've already looked this up, then use the cache
                if (idCache.ContainsKey(tableName))
                {
                    id = idCache[tableName];
                }
                //if we havn't looked this up before get it and add it to the cache
                else
                {
                    id = this.UniqueIDs.Find(tableName, idField);
                    //if it doesn't already exist in the lookup table create a new row
                    if (id == null)
                    {
                        id = new UniqueID(tableName, idField, 1);
                        // since this is a new entry add it
                        this.UniqueIDs.Add(id);
                    }
                    else
                    {
                        // set the state to modified
                        this.Entry(id).State = System.Data.EntityState.Modified;
                    }
                }
                entry.CurrentValues[tableName + "ID"] = id.NextID;
                id.NextID = id.NextID + 1;
            }

        }
        return base.SaveChanges();
    }