Linq to sql：继承与关系-技术开发专区

Linq to sql：继承与关系

作者：lovecherry博客编辑： nancy 2008-01-25 00:00

newtopic和replies是两个GridView控件，执行效果如下图：

再来看看如何进行增删操作：

NewTopic nt = new NewTopic() { TopicTitle = "还是新主题", TopicContent = "还是新主题" };
Reply rpl = new Reply() { TopicTitle = "还是新回复", TopicContent = "还是新回复", ParentTopic = 4 };
ctx.Topics.Add(nt);
ctx.Topics.Add(rpl);
ctx.SubmitChanges();
rpl = ctx.Topics.OfType<Reply>().Single(reply => reply.TopicID == 8);
ctx.Topics.Remove(rpl);
ctx.SubmitChanges();

实体关系的定义

比如我们的论坛分类表和论坛版块表之间就有关系，这种关系是1对多的关系。也就是说一个论坛分类可能有多个论坛版块，这是很常见的。定义实体关系的优势在于，我们无须显式作连接操作就能处理关系表的条件。

首先来看看分类表的定义：

[Table(Name = "Categories")]
public class BoardCategory
{
[Column(Name = "CategoryID", DbType = "int identity",
IsPrimaryKey = true, IsDbGenerated = true, CanBeNull = false)]
public int CategoryID { get; set; }
[Column(Name = "CategoryName", DbType = "varchar(50)", CanBeNull = false)]
public string CategoryName { get; set; }
private EntitySet<Board> _Boards;
[Association(OtherKey = "BoardCategory", Storage = "_Boards")]
public EntitySet<Board> Boards
{
get { return this._Boards; }
set { this._Boards.Assign(value); }
}
public BoardCategory()
{
this._Boards = new EntitySet<Board>();
}
}

CategoryID和CategoryName的映射没有什么不同，只是我们还增加了一个Boards属性，它返回的是Board实体集。通过特性，我们定义了关系外键为BoardCategory（Board表的一个字段）。然后来看看1对多，多端版块表的实体：

[Table(Name = "Boards")]
public class Board
{
[Column(Name = "BoardID", DbType = "int identity",
IsPrimaryKey = true, IsDbGenerated = true, CanBeNull = false)]
public int BoardID { get; set; }
[Column(Name = "BoardName", DbType = "varchar(50)", CanBeNull = false)]
public string BoardName { get; set; }
[Column(Name = "BoardCategory", DbType = "int", CanBeNull = false)]
public int BoardCategory { get; set; }
private EntityRef<BoardCategory> _Category;
[Association(ThisKey = "BoardCategory", Storage = "_Category")]
public BoardCategory Category
{
get { return this._Category.Entity; }
set
{
this._Category.Entity = value;
value.Boards.Add(this);
}
}
}

第1页：概述第2页：概述第3页：概述第4页：概述第5页：概述

关注我们