业务逻辑层-Active Record

Posted 2020-12-26 lovetomato

Active Record(活动记录模式)，当系统中的业务和数据库中的表存在一一对应关系的时候，可用采用。
Active Record模式的特点：每个业务对象代表数据表中的一行数据，并且业务对象还包括了数据的增删改查的方法。

ORM

一般这种模式采用一种ORM框架，即对象关系映射。这里用的的映射是：Dapper(开源轻量级，高效率，白自动化)，Dapper需要我们写sql语法，所有是半自动化。

案例

内容管理系统中一博客系统

1. 可以发布博客

2. 对博客进行评论

   code

   代码下载

   对象实体

    public class Post
    {
        public int Id { get; set; }
        public string Subject { get; set; }
        public string Text { get; set; }
        public DateTime DateAdded { get; set; }
    }

    public class Comment
    {
        public int? Id { get; set; }
        public string Text { get; set; }
        public string Author { get; set; }
        public DateTime DateAdded { get; set; }
        public int PostId { get; set; }
    }

实体对象

    public class PostWithComment
    {
        public int Id { get; set; }
        public string Subject { get; set; }
        public string Text { get; set; }
        public DateTime DateAdded { get; set; }
        public List<Comment> Comments { get; set; }
    }

数据连接

因Dapper是对DbConnection的扩展方法，这里定义一个父类ConnectionBase,操作数据的类只需继承父类

    public abstract class ConnectionBase
    {
        public static string ConnectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

        protected SqlConnection _connection;

        protected SqlConnection connection => _connection ?? (_connection = GetOpenConnection());

        public static SqlConnection GetOpenConnection(bool mars = false)
        {
            var cs = ConnectionString;
            if (mars)
            {
                var scsb = new SqlConnectionStringBuilder(cs)
                {
                    MultipleActiveResultSets = true
                };
                cs = scsb.ConnectionString;
            }
            var connection = new SqlConnection(cs);
            connection.Open();
            return connection;
        }

        public void Dispose()
        {
            _connection?.Dispose();
        }
    }

服务

public class BlogService: ConnectionBase
    {
        public IEnumerable<Post> GetAllPosts()
        {
            string sql = "select * from Posts";
            return connection.Query<Post>(sql);
        }

        public PostWithComment GetPostWithComments(int postId)
        {
            string sql = @"select * from Posts p
                            left join Comments c on p.Id = c.PostId
                            where p.Id = @Id";
            PostWithComment result = null;
            var relust = connection.Query<PostWithComment, Comment, PostWithComment>(sql,(post,comment)=> 
            {
                if(result == null)
                {
                    result = post;
                    result.Comments = new List<Comment>();
                }
                if(comment != null)
                {
                    result.Comments.Add(comment);
                }
                return result;
            },
            new { Id=postId}).FirstOrDefault();

            return relust;
        }
    }