How to deal with Parsing Object from Join Query - mysql

Question

I'm currently working on my first API with the Perfect framework. It's been a while since I made an API myself so I must admit my SQL and API logic is a little rusty.
I'm using a MySQL database for my implementation.
For sake of example I'll explain my database structure below;
I have a table which resembles an Object, let's call this Table A. Table A has a Varchar based id as primary key.
There are 2 other tables let's call them Table B and Table C. Table A has a one to many relation to both Table B and C. Where the id of table A is the foreign key.
What I'm trying to do is obtain everything with one query and cast it to an object in my backend.
By using outer joins I'm making the call to retrieve all the required data.
SELECT control.id, control.type, control.description, control.address, control.city, control.created, control.updated, control.latitude, control.longitude, images.id AS image_id, images.image, images.description AS image_description, updates.id AS update_id, updates.still_present, updates.created_at AS update_created
FROM Control control left outer join control_images images
ON control.id=images.control_id
left outer join Control_Updates updates
ON control.id=updates.control_id
Now is my question what would be the best way to store this data in an object that holds an array of updates and an array of images.
Before writing the join query I only attempted to get the values from Table A I used the following code to cast the results to my desired object.
let result = mysql.storeResults()
let checkResult = self.checkResult(result: result, response: response)
response = checkResult.response
var controls: [Control] = []
while let row = result?.next() {
let type = Types(rawValue: row[1].unwrap)!
let control = Control(id: row[0].unwrap, type: type, description: row[2].unwrap, address: row[3].unwrap, city: row[4].unwrap, latitude: Double(row[7].unwrap).unwrap, longitude: Double(row[8].unwrap).unwrap)
controls.append(control)
}
obviously this will just return duplicate objects apart from the images and updates of course.
I'm wondering if this is the best way to do it or if I should call a new query in the while loop

Answer 1

The best way to resolve this issue, by still only using one query and one loop is by using 'hashmaps'. I'm not familiar with Perfect framework, but in PHP it would look something like:
// Get results from the db:
$results = $db->execute($query, $params);
// Define map for controls:
$map = [];
// Loop over results/rows
foreach($results as $row){
// Get unique identifier for the Control model:
$controlId = $row['id'];
// Check if control is NOT already in map:
if(!isset($map[$controlId]){
// Add control to map:
$control = [
'id' => $controlId,
'description' => $row['description'],
'images' => []
// other fields
];
// Add control to map:
$map[$controlId] = $control;
}
else{
// Control exists, retrieve it from the map:
$control = $map[$controlId];
}
// Retrieve unique identifier of the image:
$imageId = $row['image_id'];
// Same tactic with hasmap, check if control already has the image, if not add it
if(!isset($control['images'][$imageId]){
// add the image to the hashmap:
}
else{
// Image is already added, the content from the 'update' data is not added yet, handle that part (also with a hash map)
}
}
Hope that helps you figure it out in Perfect framework