Install-Package MySql.Data -Version 8.0.15

Microsoft.AspNetCore.All
MySql.Data.EntityFrameworkCore、
Dapper
Microsoft.Extensions.Configuration.Abstractions
Microsoft.Extensions.Configuration.FileExtensions
Microsoft.Extensions.Configuration.Json

 "ConnectionStrings": {
  "DefaultConnection": "server=服务器;port=端口号;database=regatta{0};SslMode=None;uid=userName;pwd=passWord;Allow User Variables=true"
 },

public class BaseRepository : IDisposable
  {
    public static IConfigurationRoot Configuration { get; set; }

    private MySqlConnection conn;

    public MySqlConnection GetMySqlConnection(int regattaId = 0, bool open = true,
      bool convertZeroDatetime = false, bool allowZeroDatetime = false)
    {
      IConfigurationBuilder builder = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json");

      Configuration = builder.Build();
      

      string cs = Configuration.GetConnectionString("DefaultConnection");
      cs = regattaId == 0 "_" + regattaId.ToString());

      cs = cs.Replace("userName", "真正的账号").Replace("passWord", "真正的密码");
      var csb = new MySqlConnectionStringBuilder(cs)
      {
        AllowZeroDateTime = allowZeroDatetime,
        ConvertZeroDateTime = convertZeroDatetime
      };
      conn = new MySqlConnection(csb.ConnectionString);
      return conn;
    }
public void Dispose()
{
if (conn != null && conn.State != System.Data.ConnectionState.Closed)
{
conn.Close();
}
}

}

  /// <summary>
    /// 根据赛事Id、用户Id获取用户基本信息
    /// </summary>
    /// <param name="regattaId">赛事Id</param>
    /// <param name="userId">用户Id</param>
    /// <returns></returns>
    public async Task<实体对象> FindUserByAccount(int regattaId, int userId)
    {
      try
      {
        var cmdText =
          @"select b.id_number as IdentifierId,b.isvalid as Isvalid,a.name as Name,a.userid as InternalId,a.sex as Sexual,a.sex as SexTypeId,a.age as Age,
                c.isprofessional as IsProfessional,c.role_type as RoleTypeId,a.weight as Weight,a.height as Height, a.phone as PhoneNumber,a.thumb_image as ThubmnailImage,
                a.image as Image,c.athlete_id as AthleteId from 表1 a left join 表2 b on a.userid=b.id 
                left join 表3 c on b.id=c.centralid where a.userid=@userId;";
　　　　　　　　　　//此处可以根据传入的regattaId访问不同的数据库
        using (var conn = GetMySqlConnection(regattaId))
        {
          if (conn.State == ConnectionState.Closed)
          {
            await conn.OpenAsync();
          }

          var memberModel = conn
            .Query<实体对象>(cmdText, new { userId = userId }, commandType: CommandType.Text)
            .FirstOrDefault();
          return memberModel "FindUserByAccount by Id Failed!");
        throw;
      }


    }

public async Task<bool> DeleteXXX(int regattaId, int id, int userId)
    {
      var result = false;
      using (var conn = GetMySqlConnection(regattaId))
      {
        if (conn.State == ConnectionState.Closed)
        {
          await conn.OpenAsync();
        }

        using (var transaction = conn.BeginTransaction())
        {
          try
          {
            const string sqlDelClub =
              @"delete from 表名 where 字段1=@clubId;
               delete from 表名2 where 字段2=@clubId;
               delete from 表名3 where 字段3=@userId and clubinfo_id=@clubId;";

            await conn.QueryAsync(sqlDelClub, new
            {
              clubId = id,
              userId = userId,
            }, commandType: CommandType.Text);

            transaction.Commit();

            result = true;
          }
          catch (Exception e)
          {
            Console.WriteLine(e);
            transaction.Rollback();
            result = false;
            throw;
          }
        }

        return result;
      }
    }

public async Task<List<实体 GetClubsByUserId(int regattaId, int userId)
    {
      using (var conn = GetMySqlConnection(regattaId))
      {
        if (conn.State == ConnectionState.Closed)
        {
          await conn.OpenAsync();
        }

        const string sql =
          @"select b.club_id as id,c.name,c.image as ImageData,c.year,c.address,c.creator,c.description,b.contact ,b.phone,b.isvalid from 表1 a left join 表2 b on 
           a.clubinfo_id=b.club_id left join 表3 c on 
           b.clubbase_id=c.club_id where a.authorize_userid=@user_Id";
        List<实体> clubDetailList =
          (await conn.QueryAsync<实体>(sql, new { user_Id = userId }, commandType: CommandType.Text))
          .ToList();

        return clubDetailList;
      }
    }