php mysql检查连接是否已建立

Question

This question differs from checking if the specific connection is alive or not which I found in SO itself and in Google Search Resutls.

What I want is to check if the mysql connection has already been established. I need to check this, because I have many modules which needs connection to function. The same module is sometimes called where there is no connection and sometimes called when there is already an connection.

Answer 1

I suggest use singleton pattern and some OO.

class Singleton{
    private static $instance=null;
    public function connection(){
        if(self::$instance==null){
            self::$instance = mysql_connect(); 
    }
        return self::$connection;
    }
}

class TableA extends Singleton{
    function find($id){
        $query="select * from `A` where `id`='$id'";
        mysql_query($query, $this->connection());
        ... // other codes
    }
}

hope that will help you

Answer 2

You should simply call mysql_connect with the same arguments. If an identical connection already exists, it will simply be reused.

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That was the lazy answer. Obviously the better way would be to structure your program in a way that you know what your program's status is. Getting rid of the age-old, deprecated mysql_ extension is a first step. Use mysqli or PDO, both of which do not support implicit connections but require you to hand a variable around that represents your connection. That's what you should do anyway for a sane and modular application structure, then you would not have these kinds of questions.