Dapper的基本使用
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 FORM 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Rollback
transaction.Rollback();
throw new Exception(ex.Message);
}
}