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  • Dapper的基本使用 [转]

    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:

    1. 使用Dapper可以自动进行对象映射!
    2. 轻量级,单文件。
    3. 支持多数据库。
    4. 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}]	"{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Rollback
        transaction.Rollback();
        throw new Exception(ex.Message);
      }
    }

    文章来源 https://www.cnblogs.com/Sinte-Beuve/p/4231053.html

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  • 原文地址:https://www.cnblogs.com/kerwincui/p/9328128.html
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