如何在php项目中连接多个数据库

由于您已经使用默认值初始化了类中的数据成员，因此您可以选择性地让构造函数接受连接参数，例如：Database

class Database
{
    public $host   = DB_HOST;
    public $user   = DB_USER;
    public $pass   = DB_PASS;
    public $dbname = DB_NAME;


    public $link;
    public $error;

    public function __construct(
        $host = NULL,
        $user = NULL,
        $pass = NULL,
        $dbname = NULL
    )
    {
        $this->host = $host ?? $this->host;
        $this->user = $user ?? $this->user;
        $this->pass = $pass ?? $this->pass;
        $this->dbname = $dbname ?? $this->dbname;
        
        $this->connectDB();
    }

    private function connectDB()
    {
        $this->link = new mysqli(
            $this->host,
            $this->user,
            $this->pass,
            $this->dbname
        );
        if (!$this->link) {
            $this->error = "Connection fail" . $this->link->connect_error;
            return false;
        }
    }
}

这样，只有更改的值才会更新，因此，如果同一主机上有两个数据库，则只需传递参数而保持其他数据库不变。$dbname

$connection_1 = new Database();
$connection_2 = new Database(dbname: "my_other_database");

另一种解决方案是保持原始代码不更改它，但每次都包含不同的配置文件，它仍然可以正常工作。

如果您要将所有数据库连接详细信息存储在一个文件中（作为 JSON ），您可以执行如下操作。

<?php
    /*
        connection details for each database
        in JSON format. This could be saved
        as, for instance, db-credentials.json 
        -------------------------------------
        
        {
            "db1":{
                "dbuser":"dbo-764931",
                "dbhost":"localhost",
                "dbpwd":"xxx",
                "dbname":"blackrock"
            },
            "db2":{
                "dbuser":"dbo-984633",
                "dbhost":"localhost",
                "dbpwd":"xxx-yyy",
                "dbname":"area51"
            }
        }
        
    */
    
    
    
    
    class Database{
        private static $instance=false;
        private $db;
        
        private function __construct( $dbhost, $dbuser, $dbpwd, $dbname ){
            mysqli_report( MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT );
            $this->db=new mysqli( $dbhost, $dbuser, $dbpwd, $dbname );
        }
        public static function initialise( $dbhost, $dbuser, $dbpwd, $dbname ){
            if( !self::$instance ) self::$instance=new self( $dbhost, $dbuser, $dbpwd, $dbname );
            return self::$instance;
        }
    }
    
    class Credentials{#class to read the db connection details for given $db
        private $json;
        private $db;
        
        public function __construct( $file, $db ){
            $this->json=file_exists( $file ) ? json_decode( file_get_contents( $file ) ) : false;
            $this->db=$db;
        }
        public function fetch(){
            return is_object( $this->json ) && property_exists( $this->json,$this->db ) ? $this->json->{$this->db} : false;
        }
    }
    
    class Model{
        private $db;
        private $config;
        
        public function __construct( $config,$db ){
            $credentials=new Credentials( $config,$db );
            $obj=$credentials->fetch();
            $this->db=Database::initialise( $obj->dbhost, $obj->dbuser, $obj->dbpwd, $obj->dbname );
        }
        public function employee_list(){
            $sql='SELECT * FROM emp_list ORDER BY emp_id DESC';
            return $this->db->query( $sql )->fetch_all( MYSQLI_ASSOC );
        }
    }








    # only to show result
    function debug($obj){
        printf('<pre>%s</pre>',print_r($obj,true));
    }








    $config = __DIR__ . '/db-credentials.json';

    $model_1=new Model( $config, 'db1' );
    $model_2=new Model( $config, 'db2' );
    
    
    debug( $model_1 );
    debug( $model_2 );
?>

测试上述产量：

Model Object
(
    [db:Model:private] => Database Object
        (
            [db:Database:private] => mysqli Object
                (
                    [affected_rows] => 0
                    [client_info] => mysqlnd 5.0.12-dev - 20150407 - $Id: 38fea24f2847fa7519001be390c98ae0acafe387 $
                    [client_version] => 50012
                    [connect_errno] => 0
                    [connect_error] => 
                    [errno] => 0
                    [error] => 
                    [error_list] => Array
                        (
                        )

                    [field_count] => 0
                    [host_info] => localhost via TCP/IP
                    [info] => 
                    [insert_id] => 0
                    [server_info] => 5.5.8
                    [server_version] => 50508
                    [stat] => Uptime: 2210764  Threads: 3  Questions: 702637  Slow queries: 11  Opens: 12000  Flush tables: 1  Open tables: 256  Queries per second avg: 0.317
                    [sqlstate] => 00000
                    [protocol_version] => 10
                    [thread_id] => 52276
                    [warning_count] => 0
                )

        )

    [config:Model:private] => 
)

...省略的输出。$model_2

使用这样的方法，您可以编辑连接详细信息，而无需稍后修改类，并且可以根据需要使用任意数量的不同数据库。