<"`{$this->_database}`.`{$this->_tablename}`";
    $this->isRelease = $isRelease;
  }
  public static function getInstance($database='', $tablename='', $isRelease=0)
  {
    if (self::$Instance == null) {
      self::$Instance = new DBRWmysql($database, $tablename, $isRelease);
    }
    self::$Instance->_database = $database;
    self::$Instance->_tablename = $tablename;
    self::$Instance->_dt    = "`{$database}`.`{$tablename}`";
    self::$Instance->isRelease = $isRelease;
    return self::$Instance;
  }
  //如果主机没变,并且已经存在MYSQL连接,就不再创建新的连接
  //如果主机改变,就再生成一个实例创建一个连接
  //type == 'write'或'read'
  public function getLink($type)
  {
    $this->dbType = $$type;
    //随机选取一个数据库连接(区分读写)
    $dbConfig = DBConfig::$$type;
    $randKey = array_rand($dbConfig);
    $config = $dbConfig[$randKey];
    //链接数据库
    $host = $config['host'];
    $username = $config['username'];
    $password = $config['password'];
    if (empty($this->links[$host])) {
      $this->_host = $host;
      $this->links[$host] = new mysqli($host, $username, $password);
      if($this->links[$host]->connect_error) {
        $this->error($this->links[$host]->connect_error);
      }
    }
    //初始化链接
    $this->link = $this->links[$host];
    $this->link->query("set names utf8mb4;"); //支持emoji表情
    $this->link->query("use {$this->_database};");
  }
  public function getCurrentLinks()
  {
    return $this->links;
  }
  //析构函数
  public function __destruct()
  {
    foreach ($this->links as $v) {
      $v->close();
    }
  }
  //查询封装
  public function query($sql)
  {
    $this->sql = $sql;
    if (strpos($sql, 'select') !== false) {
      $this->getLink('read');//读库
    } else {
      $this->getLink('write');//写库
    }
    $this->rs = $this->link->query($sql);
    ($this->rs === false) && $this->error('sql error: '.$sql.PHP_EOL.$this->link->error);
    //查询完成后释放链接, 并删除链接对象
    if ($this->isRelease) {
      $this->link->close();
      unset($this->links[$this->_host]);
    }
    return $this->rs;
  }
  //增
  public function insert($arrData)
  {
    foreach ($arrData as $key=>$value) {
      $fields[] = $key;
      $values[] = "'".$value."'";
      // $fields[] = '`'.$key.'`';
      // $values[] = "'".$value."'";
    }
    $strFields = implode(',', $fields);
    $strValues = implode(',', $values);
    $sql = "insert into {$this->_dt} ($strFields) values ($strValues)";
    $this->query($sql);
    $insert_id = $this->link->insert_id;
    return $insert_id;
  }
  //增
  public function replace($arrData)
  {
    foreach ($arrData as $key=>$value) {
      $fields[] = $key;
      $values[] = "'{$value}'";
    }
    $strFields = implode(',', $fields);
    $strValues = implode(',', $values);
    $sql = "replace into {$this->_dt} ($strFields) values ($strValues)";
    $this->query($sql);
    return $this->link->insert_id;
  }
  //增
  //每次插入多条记录
  //每条记录的字段相同,但是值不一样
  public function insertm($arrFields, $arrData)
  {
    foreach ($arrFields as $v) {
      // $fields[] = "`{$v}`";
      $fields[] = $v;
    }
    foreach ($arrData as $v) {
      $data[] = '('.implode(',', $v).')';
    }
    $strFields = implode(',', $fields);
    $strData = implode(',', $data);
    $sql = "insert into {$this->_dt} ($strFields) values {$strData}";
    $this->query($sql);
    return $this->link->insert_id;
  }
  //删
  public function delete()
  {
    $where = $this->getWhere();
    $limit = $this->getLimit();
    $sql = " delete from {$this->_dt} {$where} {$limit}";
    $this->query($sql);
    return $this->link->affected_rows;
  }
  //改
  public function update($data)
  {
    $where = $this->getWhere();
    $arrSql = array();
    foreach ($data as $key=>$value) {
      $arrSql[] = "{$key}='{$value}'";
    }
    $strSql = implode(',', $arrSql);
    $sql = "update {$this->_dt} set {$strSql} {$where} {$this->limit}";
    $this->query($sql);
    return $this->link->affected_rows;
  }
  //获取总数
  public function getCount()
  {
    $where = $this->getWhere();
    $sql = " select count(1) as n from {$this->_dt} {$where} ";
    $resault = $this->query($sql);
    ($resault===false) && $this->error('getCount error: '.$sql);
    $arrRs = $this->rsToArray($resault);
    $num = array_shift($arrRs);
    return $num['n'];
  }
  //将结果集转换成数组返回
  //如果field不为空，则返回的数组以$field为键重新索引
  public function rsToArray($field = '')
  {
    $arrRs = $this->rs->fetch_all(MYSQLI_ASSOC); //该函数只能用于php的mysqlnd驱动
    $this->rs->free();//释放结果集
    if ($field) {
      $arrResult = [];
      foreach ($arrRs as $v) {
        $arrResult[$v[$field]] = $v;
      }
      return $arrResult;
    }
    return $arrRs;
  }
  //给字段名加上反引号
  public function qw($strFields)
  {
    $strFields = preg_replace('#\s+#', ' ', $strFields);
    $arrNewFields = explode(' ', $strFields );
    $arrNewFields = array_filter($arrNewFields);
    foreach ($arrNewFields as $k => $v) {
      $arrNewFields[$k]= '`'.$v.'`';
    }
    return implode(',', $arrNewFields);
  }
  //处理入库数据,将字符串格式的数据转换为...格式(未实现)
  public function getInsertData($strData)
  {
    // $bmap = "jingdu,$jingdu weidu,$weidu content,$content";
  }
  //select in
  //arrData 整数数组，最好是整数
  public function select_in($key, $arrData, $fields='')
  {
    $fields = $fields "(select $fields from {$this->_dt} where $key between $s and $e)";
      } else {
        $s = $v[0];
        $sql = "(select $fields from {$this->_dt} where $key = $s)";
      }
      $arrSql[] = $sql;
    }
    $strUnion = implode(' UNION ALL ', $arrSql);
    $res = $this->query($strUnion);
    return $this->rstoarray($res);
  }
  //where in
  public function setWhereIn($key, $arrData)
  {
    if (empty($arrData)) {
      $str = "(`{$key}` in ('0'))";
      $this->addWhere($str);
      return $str;
    }
    foreach ($arrData as &$v) {
      $v = "'{$v}'";
    }
    $str = implode(',', $arrData);
    $str = "(`{$key}` in ( {$str} ))";
    $this->addWhere($str);
    return $this;
  }
  //where in
  public function setWhere($arrData)
  {
    if (empty($arrData)) {
      return '';
    }
    foreach ($arrData as $k => $v) {
      $str = "(`{$k}` = '{$v}')";
      $this->addWhere($str);
    }
    return $this;
  }
  //between and
  public function setWhereBetween($key, $min, $max)
  {
    $str = "(`{$key}` between '{$min}' and '{$max}')";
    $this->addWhere($str);
    return $this;
  }
  //where a>b
  public function setWhereBT($key, $value)
  {
    $str = "(`{$key}` > '{$value}')";
    $this->addWhere($str);
    return $this;
  }
  //where a<b
  public function setWhereLT($key, $value)
  {
    $str = "(`{$key}` < '{$value}')";
    $this->addWhere($str);
    return $this;
  }
  //组装where条件
  public function addWhere($where)
  {
    $this->arrWhere[] = $where;
  }
  //获取最终查询用的where条件
  public function getWhere()
  {
    if (empty($this->arrWhere)) {
      return 'where 1';
    } else {
      return 'where '.implode(' and ', $this->arrWhere);
    }
  }
  //以逗号隔开
  public function setFields($fields)
  {
    $this->fields = $fields;
    return $this;
  }
  // order by a desc
  public function setOrder($order)
  {
    $this->arrOrder[] = $order;
    return $this;
  }
  //获取order语句
  public function getOrder()
  {
    if (empty($this->arrOrder)) {
      return '';
    } else {
      $str = implode(',', $this->arrOrder);
      $this->order = "order by {$str}";
    }
    return $this->order;
  }
  //e.g. '0, 10'
  //用limit的时候可以加where条件优化：select ... where id > 1234 limit 0, 10
  public function setLimit($limit)
  {
    $this->limit = 'limit '.$limit;
    return $this;
  }
  //直接查询sql语句, 返回数组格式
  public function arrQuery($sql, $field='')
  {
    $this->query($sql);
    $this->clearQuery();
    ($this->rs===false) && $this->error('select error: '.$sql);
    return $this->rsToArray($field);
  }
  //如果 $field 不为空, 则返回的结果以该字段的值为索引
  //暂不支持join
  public function get($field='')
  {
    $where = $this->getWhere();
    $order = $this->getOrder();
    $sql = " select {$this->fields} from {$this->_dt} {$where} {$order} {$this->limit} ";
    return $this->arrQuery($sql, $field);
  }
  //获取一条记录
  public function getOne()
  {
    $this->setLimit(1);
    $rs = $this->get();
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