面向对象封装mysqli操作类

增删改查，删除就不写了，一般都是软删除，可以合并到update中

<?php
class db {
    public $connect;

    public function __construct() {
        try {
            $host = '127.0.0.1';
            $user = 'root';
            $password = 'root';
            $database = 'test';
            $this->connect =  mysqli_connect($host, $user,$password);
            if (empty($this->connect)) {
                die('数据库配置错误');
            }
            if (!mysqli_select_db($this->connect, $database)) {
                die('数据库错误');
            }
            mysqli_query($this->connect,"set names utf8;");
        } catch (Exception $e) {
            die($e->getMessage() . $e->getFile() . $e->getLine());
        }
    }

    public function __destruct() {
        mysqli_close($this->connect);
    }

    /**
     * 判断数据表是否存在
     * @param $table
     * @return bool
     */
    public function isTableExist($table)
    {
        $sql = "show tables";
        $result = mysqli_query($this->connect, $sql);
        $data = [];
        while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
            $row = array_values($row);
            $data[] = $row[0];
        }
        if (empty($data)) {
            return false;
        }
        if (!in_array($table, $data)) {
            return false;
        }
        return true;
    }

    /**
     * 插入数据库
     */
    public function add ($table, $insertData) {
        if (!empty($table) && count($insertData) > 0) {
            $column = '';
            $insertValue = '';
            foreach ($insertData as $key => $value) {
                $column .= ',`' . $key . '`';
                $insertValue .= ",'" . $value . "'";
            }
            $sql = 'insert into ' . $table . ' ( ' . trim($column, ',') . ') values (' . trim($insertValue, ',') . ')';
            mysqli_query($this->connect, $sql);
            return mysqli_insert_id($this->connect);
        }
        return 0;
    }

    /**
     * 修改数据
     * @param string $table 表名
     * @param array $condition  更新条件
     * @param array $updateData 更新数据
     * @return bool|mysqli_result
     */
    public function update (string $table, array $condition, array $updateData) {
        if (!self::isTableExist($table)) {
            return false;
        }
        if (empty($condition) || empty($updateData)) {
            return false;
        }
        $sql = "update `$table` set ";
        $updateArr = [];
        foreach ($updateData as $key => $value) {
            $updateArr[] = " `$key` = '$value' ";
        }
        $sql .= implode(',', $updateArr);
        $whereArr = [];
        foreach ($condition as $key => $value) {
            $whereArr[] = " `$key` = '$value' ";
        }
        $sql .= " where " . implode(' and ', $whereArr);
        return mysqli_query($this->connect, $sql);
    }

    /**
     * 查询数据
     * @param string $table 数据表
     * @param array $field  要查询的字段
     * @param array $where  查询条件
     * @return array
     */
    public function select(string $table, array $field = ['*'], array $where = []) {
        if (mysqli_query($this->connect, $table)) {
            return [];
        }
        if (in_array('*', $field)) {
            $fields = '*';
        } else {
            $fields = implode(',', $field);
        }
        $sql = "select $fields from `$table`";
        if (!empty($where)) {
            $whereArr = [];
            foreach ($where as $key => $value) {
                $whereArr[] = " `$key` = '$value' ";
            }
            $sql .= " where " . implode(' and ', $whereArr);
        }
        $result = mysqli_query($this->connect, $sql);
        if (empty($result)) {
            return [];
        }
        $data = [];
        while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
            $data[]=  $row;
        }
        return $data;
    }
}