如何在php中创建一个空白的关联数组

Question

My php script returns data to the web client where it is processed by javaScript.

If data is found it is stored in an associative array / object. If no data is found I would like to send a blank associative array.

The only example I have seen on line is in the manual where you create an empty class and then instantiate an object from that.

Below is my code and the results it produces on the web client side

            $sql = 'select job, client, project from jobs j left join client c on c.key = j.cKey where j.key='.$this->p['reckey'];
        if ( $result = $db->query($sql) )
        {
            if ($result->num_rows > 0)
            {
                $l = mysqli_fetch_all( $result, $resulttype = MYSQLI_ASSOC );
                $this->res_array['info'] = $l[0];
            }else{
                $this->errors[] = 'No such job # '.$this->p['reckey'];
                $this->res_array['info']=[];
            }
        }else{
            $this->errors[] = 'Query failed!';
            $this->res_array['info']=[];
        }
        $this->res_array['errors'] = $this->errors;
        echo json_encode ($this->res_array);

Here are two examples of what the data looks like when it arrives at the web client before it is decoded by JSON. Note the difference in the "info" element.

response { "info":{"job":"999","client":"My Company, Inc. ","project":"This Project"} ,"errors":[]}

error response { "info":[ ] ,"errors":["No such job # 0"]}

In the successful response I have an object/associative array where I would use the

for (variable in object) {...}

In the blank response I just get the standard array [ ] square brackets where I would use the

for (step = 0; step < info.length; step++) {}

This occurs of course because I am specifying a blank array in the php code above.

My question is simple how can I change my php code so a blank associtive array is transmitted?

Answer 1

The only example I have seen on line is in the manual where you create an empty class and then instantiate an object from that.

Sounds like you've answered your own question!

Since in JavaScript an object and an associative array are basically the same thing all you have to do is replace this line:

$this->res_array['info']=[];

With this one:

$this->res_array["info"] = new StdClass;

Or if you want to make the change only before sending the response you could check for an empty info array and replace it with an empty class.

if(!count($this->res_array["info"]))
    $this->res_array["info"] = new StdClass;

Answer 2

I would suggest to take the best of both worlds, and let PHP generate an array of associative arrays, even though you expect at the most one, but at least you'd use the same structure for when you have none.

So change:

$this->res_array['info'] = $l[0];

to:

$this->res_array['info'] = $l;

And then in JavaScript do:

for (var step = 0; step < info.length; step++) {
    for (variable in info[step]) {
        // ...
    }
}

... and if you still need to, you can deal with the no-data condition separately in JavaScript. Something like:

if (errors.length) {
    // deal with this case...
}