ASP.NET Core 2.1 下采用Dapper检索数据

假如你喜欢原生的Sql语句,又喜欢ORM的简单,那你一定会喜欢上Dapper这款数据访问组件。

开始吧，安装 dapper。

$ dotnet add package dapper

这里有一个表叫 org_depart(部门表) ,包含 部门代码、部门名称等等，这里采用类 Depart进行映射

首先创建一个 类 Depart

    public class Depart
    {
        public int recid { get; set; }
        public string deptid { get; set; }
        public string deptname { get; set; }
        public int ref_id { get; set; }
        public DateTime established { get; set; }
        public DateTime create_date { get; set; }
        public string create_by { get; set; }
        public DateTime update_date { get; set; }
        public string update_by { get; set; }
    }

接下来我们需要创建一个 Repository (暂且翻译成数据库检索类)，取个名字叫 DepartRepository,在创建实现之前先创建一个接口IDepartRepository，这样可以采用 .net core 的依赖注入进行实例化。

public interface IDepartRepository {
    Task <Depart> GetDepartByID(int recid);

    Task <PagedList<Depart>> GetDepartList(string keyword, int ref_id, int currentPage, int pageSize);

    Task <int> AddDepart(Depart depart);

    Task <bool> UpdateDepart(int recid, Depart depart);

    bool DeleteDepart(int recid);
}

你可能注意到了这里多是 async 实现的方法，使用了 Task<> 。更多介绍可以看这里

接下来做个简单的实现示例

public class DepartRepository : IDepartRepository
{        
        public async Task<int> AddDepart(Depart depart)
        {   
           
        }
         
        public async Task<PagedList<Depart>> GetDepartList(string keyword, int ref_id, int currentPage, int pageSize)
        {
            
            
            
        }
        
}

需要更新Startup.cs ，将新创建的 DepartRepository注入到服务层

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        // 注入到服务层
        services.AddTransient<IDepartRepository, DepartRepository>();

   services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        //...
    }
}

注入IConfiguration

一般.net core 的配置都保存在appSettings.json文件中

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "ConnectionStrings": {
    "MyConnectionString": "MyConnectionString"
  }
}

问题是如何将连接字符串传递给DepartRepository，以便给Dapper用。
.net core 引入了IConfiguration类，可以注入到其他类中。这个注入的实例包含一个GetConnectionString方法可以获得连接字符串。看看下面的例子是如何注入的

public class DepartRepository : IDepartRepository
{  
    private readonly IConfiguration _config;

    public DepartRepository(IConfiguration config)
    {
        _config = config;
    }
    
    
}

上面的示例采用构造注入方式。

创建一个SqlConnection

public class DepartRepository : IDepartRepository
{
    private readonly IConfiguration _config;

    public DepartRepository(IConfiguration config)
    {
        _config = config;
    }

    public IDbConnection Connection
    {
        get
        {
            return new SqlConnection(_config.GetConnectionString("MyConnectionString"));
        }
    }
    
}

实现一个添加部门方法

public class DepartRepository : IDepartRepository
{
    public async Task<int> AddDepart(Depart depart)
        {   
            using (IDbConnection conn = Connection)
          {
            string sql = "insert into org_depart(deptid,deptname,ref_id,established,create_date,create_by,update_date,update_by) ";
            sql += "VALUES (@deptid,@deptname,@ref_id,@established,@create_date,@create_by,@update_date,@update_by); ";
            sql += "SELECT CAST(SCOPE_IDENTITY() AS INT)";
            var id = await conn.QueryAsync<int>(sql, depart);
            return  id.Single();
          }
      }
}

实现一个列表查询

public class DepartRepository: IDepartRepository {
    public async Task < PagedList < Depart >> GetDepartList(int currentPage, int pageSize) {
        using(IDbConnection conn = Connection) {

            string sql = "select * from org_depart where 1 = 1 ";

            int offset = pageSize * (currentPage - 1);

            sql = sql + " order by recid offset " + offset + " rows fetch next " + pageSize + " rows only";

            string sql_count = "select count(*) as c from org_depart where 1 = 1 ";

            int total = await conn.ExecuteScalarAsync < int > (sql_count);

            var items = await conn.QueryAsync < Depart > (sql);

            PagedList < Depart > result = new PagedList < Depart > (items.ToArray(), total);

            return result;
        }
    }
}

实现控制器

最后一步就是创建控制器，将DepartRepository注入其中。

[Route("api/[controller]")]
[ApiController] 
public class DepartController: ControllerBase {
        private readonly IDepartRepository _departRepo;
        public DepartController(IDepartRepository departRepo) {
          _departRepo = departRepo;
       } 
    
        [Route("AddDepart")]
        [HttpPost]
         public async Task < ApiResult > AddDepart(Depart model) {
        if (!ModelState.IsValid) {
            return ApiResultUtil.Fail("数据不合法!");
        }
        try {
            var result = await _departRepo.AddDepart(model);

            if (result > 0) {
                return ApiResultUtil.Success < int > (result);
            } else {
                return ApiResultUtil.Fail("新增部门失败！");
            }

        } catch(Exception ex) {
            return ApiResultUtil.Fail("新增部门失败！");
        }
      }
}

Github上的样例

摘自：https://exceptionnotfound.net/using-dapper-asynchronously-in-asp-net-core-2-1/