Mysql relationship between tables

Question

I have a question to now what is the best solution to make relations between tables: I have :

• client table with id name sector_id delegation_id
• sector table with id name
• delegation table with id name sector_id

My question is that is it a good practice to have both foreign keys in the client table or just the key of delegation_id is sufficient for indexing and searching in the client table (of course with join tables)

to explain more each delegation belongs to a sector. each sector belongs to a zone and each Client belongs to a delegation that belongs to a sector that is grouped in a geographical area

this is my Entity files : Class client

class Client {

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

    /**
     * @var string
     *
     * @ORM\Column(name="firstName", type="string", length=255)
     */
    private $firstName;

    /**
     * @var string
     *
     * @ORM\Column(name="lastName", type="string", length=255)
     */
    private $lastName;

    /**
     * @var string
     *
     * @ORM\Column(name="email", type="string", length=255, unique=true)
     */
    private $email;

    /**
     * @var string
     *
     * @ORM\Column(name="sector", type="string", length=255)
     */
    private $sector;

    /**
     * @var int
     *
     * @ORM\Column(name="delegation", type="integer")
     */
    private $delegation;

}

Class sector

class Sector {

    /**
     * @ORM\Id
     * @ORM\OneToMany(targetEntity="AppBundle\Entity\Delegation" ,mappedBy="sector")
     * @ORM\GeneratedValue(strategy="AUTO")
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @Assert\NotBlank()
     * @ORM\Column(type="string")
     */
    private $name;

    /**
     * @Assert\NotBlank()
     * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Zone", inversedBy="id")
     * @ORM\JoinColumn(nullable=false)
     */
    private $zone;

}

class Delegation

class Delegation {

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

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

    /**
     * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Sector", inversedBy="id" )
     * @ORM\JoinColumn(nullable=false)
     */
    private $sector;

}

Answer 1

Based on your updated question -

If each Client belongs to a Delegation , the Client entity should have a delegation_id foreign key.

If each Delegation belongs to a Sector , the Delegation entity should have a sector_id foreign key.

And if each Sector belongs to a Zone , the Sector entity should have a zone_id foreign key.

You would therefore remove your sector_id foreign key from your Client entity, and use the relationship through the Delegation entity to find all Client entities within a given Sector , if this were ever required.