如何观察DbSet 1所述的添加操作; T＆GT;？ [英] How to observe the Add action of DbSet<T>?

问题描述

我有一个名为联系方式和 ContactField 为以下两类。当 ContactField 中加入联系方式，我希望能够分配 SortOrder的到 ContactField 。我是否需要继承DbSet和定制添加的方法？如何实现的呢？

 公共类Foo {
        私人MyDbContext _db =新MyDbContext（）;

        公共无效的HelloWorld（）{
            联系方式联系方式= ....; //＆LT;从数据库中的联系人。

            ContactField场= ....; ///＆LT;新领域
            ... ///＆LT;分配其他的属性到这个`field`
            field.FieldType = FieldType.Phone;

            //如何自动更新'SortOrder`
            //添加场到`ContactFields`时
            contact.ContactFields.Add（场）;

            _db.SaveChanges（）;
        }
}

公共类联系{
        众长的ContactID {获得;组; }

        公共字符串显示名称{获得;组; }
        公共字符串DisplayCompany {获得;组; }
        公开日期时间CreatedTime {获得;组; }
        公开日期时间ModifiedTime {获得;组; }

        //原来的codeS
        //公共虚拟的ICollection＆LT; ContactField＆GT; ContactFields {获得;组; }
        公共虚拟MYLIST＆LT; ContactField＆GT; ContactFields {获得;组; }
}

 公共类ContactField {
        众长ContactFieldID {获得;组; }
        公众诠释SortOrder的{获得;组; }
        公众诠释的FieldType {获得;组; }

        公共字符串值{获得;组; }
        公共字符串标签{获得;组; }

        [专栏（的ContactID）
        公众诠释的ContactID {获得;组; }
        公共虚拟联络联系{获得;组; }
 }
 

编辑：     我发现我需要的是监督的变化的ICollection＆LT; ContactField＆GT; ContactFields 。而名单，其中，T＆GT; 是的ICollection＆LT的实现; T＆GT; 。所以，我创建一个自定义的 MYLIST ，并要求其通知 MYLIST 容器的变化。我将测试它的工作原理或不晚。

 公共类MYLIST＆LT; TEntity＆GT; ：列表＆LT; TEntity＆GT; {
        公共委托OnAddHandler（对象发件人，TEntity项）;
        公共事件OnAddHandler OnAddEvent;

        大众新空加（TEntity实体）{
             OnAddEvent（这一点，实体）;
             base.Add（实体）;
        }
 }
 

解决方案

该DbSet拥有的本地属性，它是一个的ObservableCollection 。您可以订阅 Col​​lectionChanged 事件和更新排序顺序出现。

 公共类Foo {
        私人MyDbContext _db =新MyDbContext（）;

        公共无效的HelloWorld（）{

            _db.Contacts.Local.CollectionChanged + = ContactsChanged;

            联系方式联系方式= ....; //＆LT;从数据库中的联系人。

            ContactField场= ....; ///＆LT;新领域
            ... ///＆LT;分配其他的属性到这个`field`
            field.FieldType = FieldType.Phone;

            //如何自动更新'SortOrder`
            //添加场到`ContactFields`时
            contact.ContactFields.Add（场）;

            _db.SaveChanges（）;
        }

        公共无效ContactsChanged（对象发件人，NotifyCollectionChangedEventArgs参数）{

            如果（args.Action == NotifyCollectionChangedAction.Add）
            {

                // 分类
            }
        }
}
 

I has two classes named Contact and ContactField as following. When the ContactField is added into Contact, I hope to assign SortOrder to ContactField automatically. Do I need to inherit DbSet and customize the Add method ? How to achieve it ?

public class Foo {
        private MyDbContext _db = new MyDbContext();

        public void HelloWorld() {
            Contact contact = ....; //< A contact from database.

            ContactField field = ....; ///< A new field 
            .... ///< assign other properties into this `field`
            field.FieldType = FieldType.Phone;

            // How to automatically update `SortOrder` 
            // when adding field into `ContactFields`
            contact.ContactFields.Add(field);

            _db.SaveChanges();
        }
}

public class Contact {
        public long ContactID { get; set; }

        public string DisplayName { get; set; }
        public string DisplayCompany { get; set; }
        public DateTime CreatedTime { get; set; }
        public DateTime ModifiedTime { get; set; }

        // Original codes    
        //public virtual ICollection<ContactField> ContactFields { get; set; }
        public virtual MyList<ContactField> ContactFields { get; set; }
}

 public class ContactField {
        public long ContactFieldID { get; set; }
        public int SortOrder { get; set; }
        public int FieldType { get; set; }

        public string Value { get; set; }
        public string Label { get; set; }

        [Column("ContactID")]
        public int ContactID { get; set; }
        public virtual Contact Contact { get; set; }
 }

Edit: I found what I need is to monitor the changes of ICollection<ContactField> ContactFields. And the List<T> is an implementation of ICollection<T>. So, I create a custom MyList and ask it notifies the changes of MyList container. I will test it works or not later.

public class MyList<TEntity> : List<TEntity> {
        public delegate OnAddHandler(object sender, TEntity entry);
        public event OnAddHandler OnAddEvent;

        public new void Add(TEntity entity) {
             OnAddEvent(this, entity); 
             base.Add(entity);
        }
 }

解决方案

The DbSet has a Local property which is an ObservableCollection. You can subscribe to the CollectionChanged event and update the sort order there.

public class Foo {
        private MyDbContext _db = new MyDbContext();

        public void HelloWorld() {

            _db.Contacts.Local.CollectionChanged += ContactsChanged;

            Contact contact = ....; //< A contact from database.

            ContactField field = ....; ///< A new field 
            .... ///< assign other properties into this `field`
            field.FieldType = FieldType.Phone;

            // How to automatically update `SortOrder` 
            // when adding field into `ContactFields`
            contact.ContactFields.Add(field);

            _db.SaveChanges();
        }

        public void ContactsChanged(object sender, NotifyCollectionChangedEventArgs args) {

            if (args.Action == NotifyCollectionChangedAction.Add)
            {

                // sort
            }    
        }
}

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