.NET6之MiniAPI(二十五)：Dapper

　　注：如果你使用Dapper一段时间了，这篇你可以跳过去了。

　　在第十二篇中，我们聊过官方的ORM——EntityFramework，它可以把SQL细节都隐藏，这对于一些标准化的关系数据库项目非常便捷。今天，介绍另外一个流行的ORM——Dapper，Dapper是通过扩展IDbConnection方法来达到对数据的处理的，特点是灵活，高效。

　　还是通过项目看看Dapper的使用。首先安装两个NuGet包，我们还是使用之前的Exam项目的表来说明Dapper使用，库是SQL Server。

　　安装Dapper和SqlClient：

Install-Package Dapper

Install-Package Microsoft.Data.SqlClient

　　下面是对Question进行增删改查

using Dapper;
using Microsoft.Data.SqlClient;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IQuestionService, QuestionService>();
var app = builder.Build();

app.MapPost("/question", async (IQuestionService questionService, QuestionModel question) =>
{
    return await questionService.AddQuestionAsync(question);
});

app.MapPut("/question", async (IQuestionService questionService, QuestionModel question) =>
{
    return await questionService.ModifyQuestionAsync(question);
});

app.MapGet("/question/{id}", async (IQuestionService questionService, int id) =>
{
    return await questionService.GetQuestionAsync(id);

});

app.MapDelete("/question/{id}", async (IQuestionService questionService, int id) =>
{
    return await questionService.DeleteQuestionAsync(id);
});

app.Run();

public interface IQuestionService
{
    Task<QuestionModel> GetQuestionAsync(int id);
    Task<bool> AddQuestionAsync(QuestionModel question);
    Task<bool> DeleteQuestionAsync(int id);
    Task<bool> ModifyQuestionAsync(QuestionModel question);
}
public class QuestionService : IQuestionService
{
    private readonly SqlConnection _connection;
    public QuestionService(IConfiguration configuration)
    {
        var connectionString = configuration.GetConnectionString("ExamDatabase");
        _connection = new SqlConnection(connectionString);

    }
    public async Task<bool> AddQuestionAsync(QuestionModel question)
    {
        var sql = @"INSERT INTO [Questions]
           ([Question]
           ,[Score]
           ,[QuestionTypeID]
           ,[SujectTypeID])
     VALUES
           (@Question
           ,@Score
           ,@QuestionTypeID
           ,@SujectTypeID)";
        return (await _connection.ExecuteAsync(sql, question)) > 0;
    }

    public async Task<bool> DeleteQuestionAsync(int id)
    {
        var sql = @"delete from questions where id=@id";
        return (await _connection.ExecuteAsync(sql, new { id })) > 0;
    }

    public async Task<QuestionModel> GetQuestionAsync(int id)
    {
        var sql = @"select * from questions where id=@id";
        return await _connection.QuerySingleAsync<QuestionModel>(sql, new { id });
    }

    public async Task<bool> ModifyQuestionAsync(QuestionModel question)
    {
        var sql = @"UPDATE [dbo].[Questions]
   SET [Question] = @Question
      ,[Score] = @Score
      ,[QuestionTypeID] = @QuestionTypeID
      ,[SujectTypeID] = @SujectTypeID
 WHERE ID=@ID";
        return (await _connection.ExecuteAsync(sql, question)) > 0;
    }
}

　　通过上面事例，可以看到Dapper通过扩展IDbConnection的扩展方法来提供功能，基本上查询用Query<T>(sql,Param,...)，增删改用Execute(sql,T,...)，Dapper的方便之处是T全部是自运映射到sql中的参数的，这样就能做到sql我们可以灵活且更高效语法编写，参数可以方便的进出sql，达到一个平衡点。如下图示：

 　　关于更丰富多彩的Dapper使用，详见Github仓库说明文档：https://github.com/DapperLib/Dapper

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