Controlling the output of a json feed - php

Question

I'm trying to pull out a json feed from a Wordpress query. I need the JSON to be formatted [{"id":"1","title":"title"},{"id":"2","title":"title2"}]
The json_encode function is not pulling out this specific format: Items are not separated by commas and I'm also missing the initial and final [ ]
I made this code echoing those missing elements, which works good, but the final comma, because of the echo is making the script reading it to fail.
<?php
$args = array(
'post_type' => 'location',
'posts_per_page' => -1
);
$locations = new WP_Query($args);
if($locations -> have_posts()):
echo '[';
while ($locations->have_posts()) : $locations->the_post();
$coords = get_field('coordinates');
$pid = get_the_ID();
$json["id"] = $pid;
$json["name"] = get_the_title();
$json["lat"] = $coords['lat'];
$json["lng"] = $coords['lng'];
$json["address"] = get_field('address');
$json["address2"] = get_field('address_2');
$json["city"] = get_field('city');
$json["state"] = get_field('state');
$json["postal"] = get_field('zip_code');
$json["phone"] = get_field('office_phone');
$json["fax"] = get_field('office_fax');
$json["web"] = apply_filters('the_permalink', get_permalink());
echo json_encode($json);
echo ',';
endwhile;
echo ']';
endif;
?>
I know that echoing those elements is not the correct way to do it, and I'm doing something wrong on the encode, that's why it's pulling out without the right formatting.
I have been researching for days and I couldn't find a way to create a json_encode echoing and at the same time controlling the fields that it will show from a wordpress query.
I appreciate in advance any solution/lead to solve this.

Answer 1

You're adding it wrong in your loop. What you want to do is create an array, and present that array as json.
if($locations -> have_posts()):
$data = array();
while ($locations->have_posts()) : $locations->the_post();
// add the location stuff to the $data array
$data[] = array(
'id' => $pid,
'name' => get_the_title(),
// etc....
);
endwhile;
// present your json
echo json_encode($data);
endif;