Dapper的基本使用

Dapper是.NET下一个micro的ORM，它和Entity Framework或Nhibnate不同，属于轻量级的，并且是半自动的。也就是说实体类都要自己写。它没有复杂的配置文件，一个单文件就可以了。给出官方地址。

http://code.google.com/p/dapper-dot-net/

个人觉得他非常好用，现在已经取代了原来的SqlHelper。优点：

使用Dapper可以自动进行对象映射！
轻量级，单文件。
支持多数据库。
Dapper原理通过Emit反射IDataReader的序列队列，来快速的得到和产生对象。

网上还有对Dapper的扩展类，这里就不赘述了。下面只讲下简单的增删改查、数据库表间的对应关系和事务的应用。

先给出实体类的关系：

书和书评是1---n的关系。（沿用Entity Framework的实体类，virtual表示延迟加载，此处忽略）

//书
public class Book{public Book(){Reviews = new List<BookReview>();}public int Id { get; set; }public string Name { get; set; }public virtual List<BookReview> Reviews { get; set; }public override string ToString(){return string.Format("[{0}]------《{1}》", Id, Name);}}//书评public class BookReview{public int Id { get; set; }public int BookId { get; set; }public virtual string Content { get; set; }public virtual Book AssoicationWithBook { get; set; }public override string ToString(){return string.Format("{0})--[{1}]\t\"{3}\"", Id, BookId, Content);}}

基本的增删改查操作

　　由于Dapper ORM的操作实际上是对IDbConnection类的扩展，所有的方法都是该类的扩展方法。所以在使用前先实例化一个IDBConnection对象。

IDbConnection conn = new SqlConnection(connString);

Insert

 Book book = new Book();book.Name="C#本质论";string query = "INSERT INTO Book(Name)VALUES(@name)";
//对对象进行操作conn.Execute(query, book);
//直接赋值操作conn.Execute(query, new {name = "C#本质论"});

update

string query = "UPDATE Book SET  Name=@name WHERE id =@id";conn.Execute(query, book);

delete

string query = "DELETE FROM Book WHERE id = @id";
conn.Execute(query, book);
conn.Execute(query, new { id = id });

query

 string query = "SELECT * FROM Book";
//无参数查询，返回列表，带参数查询和之前的参数赋值法相同。conn.Query<Book>(query).ToList();//返回单条信息string query = "SELECT * FROM Book WHERE id = @id";book = conn.Query<Book>(query, new { id = id }).SingleOrDefault();

数据库表对应关系操作

//查询图书时，同时查找对应的书评，并存在List中。实现1--n的查询操作
string query = "SELECT * FROM Book b LEFT JOIN BookReview br ON br.BookId = b.Id WHERE b.id = @id";
Book lookup = null;
//Query<TFirst, TSecond, TReturn>var b = conn.Query<Book, BookReview, Book>(query,(book, bookReview) =>{//扫描第一条记录，判断非空和非重复if (lookup == null || lookup.Id != book.Id)lookup = book;//书对应的书评非空，加入当前书的书评List中，最后把重复的书去掉。if (bookReview != null)lookup.Reviews.Add(bookReview);return lookup;}, new { id = id }).Distinct().SingleOrDefault();
return b;

//1--1操作 
BookReview br;
string query = "SELECT * FROM BookReview WHERE id = @id";
using (conn)
{br = conn.Query<BookReview, Book, BookReview>(query,(bookReview, book) =>{bookReview.AssoicationWithBook = book;return bookReview;}, new { id = id }).SingleOrDefault();return br;
}

事务操作

using (conn)
{
//开始事务
IDbTransaction transaction = conn.BeginTransaction();try{string query = "DELETE FROM Book WHERE id = @id";string query2 = "DELETE FROM BookReview WHERE BookId = @BookId";conn.Execute(query2, new { BookId = id }, transaction, null, null);conn.Execute(query, new { id = id }, transaction, null, null);//提交事务transaction.Commit();}catch (Exception ex){//出现异常，事务Rollbacktransaction.Rollback();throw new Exception(ex.Message);}
}

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