Symfony 3.1 - Doctrine: I am trying to add relationships between entities and thereby want to add foreign key to link tables in my example. I tried several settings, utilizing various combination of arguments, but none of them were able to ALTER the tables with Foreign key.

My entities are namely "Trips" and "Airlines" with the content attached below. I would like to use airline_id as a foreign key inside trips table. Here are the extract from my entity scripts:

Entity#1: Trips

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="trips")
 */

class Trips
{

    /**
     * @ORM\Column(name="trip_id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $trip_id;

    /**
     * @ORM\Column(name="airline_id", type="integer")
     * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Airlines")
     * @ORM\JoinColumns({
     *   @ORM\JoinColumn(name="airline_id", referencedColumnName="airline_id")
     * })
     */
    private $airline_id;

}

Entity#2: Airlines

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="airlines")
 */

class Airlines
{

    /**
     * @ORM\Column(name="airline_id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $airline_id;

    /**
     * @ORM\Column(type="string", length=80)
     */
    private $name;

}

I tried updating the schema from console , but all it says is

Nothing to update - your database is already in sync with the current entity metadata.

Also tried deleting the table and re-creating them with console; the result did not change much and the foreign key is still missing. :/

Any thoughts, or perhaps you know the solution?

I have a few suggestions, as I've gone through the same process of design. First off, should I presume that "a trip has one airline" and also "an airline has many trips"? This seems logical, and since you show @ORM\ManyToOne annotation for the Trips class, that would equate to my same presumptions.

If this is so, then these are the suggestions:

First, don't call the classes "Trips" and "Airlines", but rather in the singular, that is "Trip" and "Airline". This is object oriented thinking. So when you create a "Trip" Doctrine object, it represents a trip for example. This also makes you code more readable and also supportable from a future standpoint; as because when people read your code, they will understand that a single instance of a Trip (from the Trip class), represents a trip (that a person takes). This is important when designing code.

Given the above, make these code changes.

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="trip")
 */
class Trip
{
    /**
     * @ORM\Id
      * @ORM\Column(name="trip_id", type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $trip_id;

    /**
     * @ORM\ManyToOne(targetEntity="Airline", inversedBy="trips")
     * @ORM\JoinColumn(name="trip_airline_id", referencedColumnName="airline_id")
     */
    private $airline;
     ...
     /**
      * Set airline - Adds this trip to the passed in airline and sets the airline
      * property to resultant airline.
      *
      * @param \AppBundle\Entity\Airline
      */
     public function setAirline($airline){
         $airline->addTrip($this);
         $this->airline = $airline;
     }
}

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="airlines")
 */
class Airlines
{
    /**
     * @ORM\Column(name="airline_id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $airline_id;

    /**
     * @ORM\Column(type="string", length=80)
     */
    private $name;

     /**
      * @ORM\OneToMany(targetEntity="Trip", mappedBy="airline")
      */
     protected $trips = null;
    ...
     public function __construct(){
        // This is an array of trips.
        $this->trips = new ArrayCollection();
    }
    ...
    /**
     * Add trip - Adds a course to the array.
     */
    public function addTrip($trip){
        $this->trips[] = $trip;
    }
}

Now you can get trips from the airline, and also you can do the other way around, get the airline from the trip.

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