/// <summary>
/// 构造函数
/// </summary>
/// <param name="conString">构造参数，可以为数据库连接字符串或者DbContext</param>
/// <param name="dbType">数据库类型</param>
public DbRepository(string conString, DatabaseType dbType)
{
ConnectionString = conString;
DbType = dbType;
_db = DbFactory.GetDbContext(conString, dbType);
}