MYSQL - How to search in JSON array? - mysql

Question

On my Symfony 5 app, i've a database with a candidate table that contains a json field.
candidate 1 : [{"end": "30/04/2020", "start": "01/03/2020"},{"end": "31/07/2020", "start": "01/07/2020"}]
candidate 2 : [{"end": "31/03/2020", "start": "01/03/2020"},{"end": "31/07/2020", "start": "01/07/2020"}]
Is it possible with query builder to find a candidate where this field corresponds to the arguments ?
ex: I would like to find all the candidates who are available between 10/03/2020 and 10/04/2020.
This case should just return the candidate 1.
I guess it's not possible to do this with query builder so i'm trying to use native SQL but... what's the sql syntax ?
I tried with availability_dates`->"$.start" = "01/03/2020" but it does not work because it's a "collection".

Answer 1

This is a poorly-conceived database structure. Clearly, the JSON string represents a "repeating group" of related data, which violates the principles of so-called "normal forms."
https://en.wikipedia.org/wiki/Database_normalization
You should be storing the start/end dates in a separate table, say, candidate_dates, with columns like candidate_id, start, end. This has a so-called "one-to-many relationship" to the parent table, candidates.
Now, you can write a simple query which JOINs the two tables to get the answers you need.

Answer 2

Entity like that ?Entity like that ?
One candidate can have one or more available dates and one available dates can only be linked to one candidate.
<?php
namespace App\Entity;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
/**
* #ORM\Table(name="candidate_available_dates", uniqueConstraints={
* #ORM\UniqueConstraint(name="unique_candidate_available_dates", columns={"candidate_id", "start", "end"})
* })
*
* #ORM\Entity(repositoryClass="App\Repository\CandidateAvailableDatesRepository")
*/
class CandidateAvailableDates
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Candidate", inversedBy="candidateAvailableDates")
* #ORM\JoinColumns({
* #ORM\JoinColumn(name="candidate_id", referencedColumnName="candidate_id", nullable=false)
* })
*/
private $candidate;
/**
* #ORM\Column(type="date")
* #Assert\NotBlank
*/
private $start;
/**
* #ORM\Column(type="date")
* #Assert\NotBlank
*/
private $end;
[...]
// GETTER and SETTER
And in Candidate entity, the reversed side
/**
* #ORM\OneToMany(targetEntity="App\Entity\CandidateAvailableDates", mappedBy="candidate")
*/
private $candidateAvailableDates;