How do I get MySQL query result as nested array using PHP? - php

Question

Let's say I have this simple table where pos_level is the level of the position and pos_under is that the PID of the position on top of it.
In level 1, I have 'General Manager' and 'Supervisor'.
In level 2, under 'General Manager(PID: 1)' : 'Asst. Manager', under 'Supervisor(PID: 2)' : 'Marketing'.
In level 3, under 'Asst. manager(PID: 3)' : 'Sales' & 'Purchase', under 'Marketing(PID:2) : none.
+-----+-----------------+-----------+-----------+
| PID | pos_name | pos_level | pos_under |
+-----+-----------------+-----------+-----------+
| 1 | General Manager | 1 | 0 |
| 2 | Supervisor | 1 | 0 |
| 3 | Asst. Manager | 2 | 1 |
| 4 | Sales | 3 | 3 |
| 5 | Purchase | 3 | 3 |
| 6 | Marketing | 2 | 2 |
+-----+-----------------+-----------+-----------+
Now how do I make the query so I get a nested array as the result like this:
Array
(
[0] => Array
(
[pos_level] => 1
[pos_name] => General Manager
[pos_under] => Array
(
[0] => Array
(
[pos_level] => 2
[pos_name] => Asst. Manager
[pos_under] => Array
(
[0] => Array
(
[pos_level] => 3
[pos_name] => Sales
)
[1] => Array
(
[pos_level] => 3
[pos_name] => Purchase
)
)
)
)
)
[1] => Array
(
[pos_level] => 1
[pos_name] => Supervisor
[pos_under] => Array
(
[0] => Array
(
[pos_level] => 2
[pos_name] => Marketing
[pos_under] => Array
(
)
)
)
)
)
I have tried using multiple queries and using array_push using the results, but I have like around 100+ pos_name and I think it is messy, I have also tried using loop to keep running queries for each level and under, also tried using multiple tables for each level, but I am hoping I can use only 1 table and able to query the result as the nested array above for further use in my application.
All answers, comments, and suggestions are very welcomed. Thank you.

Answer 1

As mentioned above in the comments I doubt in general that the approach you are following is a good one. That is because it will not scale! You try to take all entries from your database and pack them into a single, hierarchical array. That means you create several copies of each entry in memory. What will happen with a growing number of entries? You face a constantly raising memory consumption of your script which will obviously make it fail ultimately.
Nevertheless I accepted the challenge and implemented a small demonstration of how to cleverly construct such nested structures with the help of references. Such references not only simplify the creation of nested structures, they also reduce the memory footprint by preventing that entries are copied by value again and again. This however will not solve the general scaling issue with this approach mentioned above, it can only help to reduce it.
I also took the liberty to make a small modification to your approach and introduce a new property "pos_over" to hold entries under an entry. Two reasons for that:
it usually is not a good idea to remove original available data and especially not to replace it with an altered meaning
the meaning of the term "pos_under" is to describe under what other entry an given entry is (to be) placed. But from the "upper" entries point of view the ones "below" it should not be referenced by "pos_under", right? That would contradict the original meaning of that term.
The following code does not depend on a database for demonstration purpose. Instead it reads the raw data from a CSV string and parses that. The actual building of the desired structure structure is marked further down by a comment. Also it should be mentioned that the code expects the original data to reference other entries only after they have been declared. So if processed from top to bottom each entry under another one can expect that other one to already exist.
Note, that the actual code to build that nested structure consists of only a mere 12 clever lines...
<?php
// the raw CSV data
$csvText = <<<CSV
PID|pos_name|pos_level|pos_under
1|General Manager|1|0
2|Supervisor|1|0
3|Asst. Manager|2|1
4|Sales|3|3
5|Purchase|3|3
6|Marketing|2|2
CSV;
// praparation of CSV data
foreach (explode("\n", $csvText) as $csvRow) {
$csvData[] = str_getcsv($csvRow, '|');
}
$csvTitle = array_shift($csvData);
$table = [];
foreach ($csvTitle as $titleKey=>$titleValue){
foreach ($csvData as $csvRow=>$csvColumn) {
foreach ($csvColumn as $csvKey=>$csvValue) {
$table[$csvRow][$csvTitle[$csvKey]] = $csvValue;
}
}
}
// creation of the structure
$catalog = [];
$structure = [];
foreach ($table as $key=>&$entry) {
$entry['pos_over'] = [];
if ($entry['pos_under'] == 0) {
$structure[] = &$entry;
$catalog[$entry['PID']] = &$structure[count($structure)-1];
} else {
$catalog[$entry['pos_under']]['pos_over'][] = &$entry;
$catalog[$entry['PID']] = &$catalog[$entry['pos_under']]['pos_over'][count($catalog[$entry['pos_under']]['pos_over'])-1];
}
}
// demonstration output
print_r($structure);
The output of above experiment is:
Array
(
[0] => Array
(
[PID] => 1
[pos_name] => General Manager
[pos_level] => 1
[pos_under] => 0
[pos_over] => Array
(
[0] => Array
(
[PID] => 3
[pos_name] => Asst. Manager
[pos_level] => 2
[pos_under] => 1
[pos_over] => Array
(
[0] => Array
(
[PID] => 4
[pos_name] => Sales
[pos_level] => 3
[pos_under] => 3
[pos_over] => Array
(
)
)
[1] => Array
(
[PID] => 5
[pos_name] => Purchase
[pos_level] => 3
[pos_under] => 3
[pos_over] => Array
(
)
)
)
)
)
)
[1] => Array
(
[PID] => 2
[pos_name] => Supervisor
[pos_level] => 1
[pos_under] => 0
[pos_over] => Array
(
[0] => Array
(
[PID] => 6
[pos_name] => Marketing
[pos_level] => 2
[pos_under] => 2
[pos_over] => Array
(
)
)
)
)
)