Link Multiple field with Primary

Sometimes you have a hasMany relationship and need to have the ability to a select primary record among related ones. As example, a Contacts field of the Case entity.

Need to create a contacts linkMultiple field with a primary for our custom entity Stock.

Step 1

Create (or edit) custom/Espo/Custom/Resources/metadata/entityDefs/Stock.json:

{
    "fields": {
        "contacts": {
            "type": "linkMultiple",
            "view": "custom:views/stock/fields/contacts"
        },
        "contact": {
            "type": "link"
        }
    },
    "links":{
        "contact": {
            "type": "belongsTo",
            "entity": "Contact",
            "foreign": "stocksPrimary"
        },
        "contacts": {
            "type": "hasMany",
            "entity": "Contact",
            "foreign": "stocks",
            "layoutRelationshipsDisabled": true
        }
    }
}

Step 2

custom/Espo/Custom/Resources/metadata/entityDefs/Contact.json

{
    "links":{
        "stocksPrimary": {
            "type": "hasMany",
            "entity": "Stock",
            "foreign": "contact",
            "layoutRelationshipsDisabled": true
        },
        "stocks": {
            "type": "hasMany",
            "entity": "Stock",
            "foreign": "contacts"
        }
    }
}

Step 3

custom/Espo/Custom/Hooks/Stock/AfterSave.php

<?php
namespace Espo\Custom\Hooks\Stock;

use Espo/ORM/Entity;
use Espo/ORM/EntityManager;

class AfterSave
{
    public function __construct(private EntityManager $entityManager) {}

    public function afterSave(Entity $entity, array $options): void
    {            
        if (!$entity->isAttributeChanged('contactId')) {
            return;
        }

        $contactId = $entity->get('contactId');
        $fetchedContactId = $entity->getFetched('contactId');

        $relation = $this->entityManager
            ->getRDBRepository($entity->getEntityType())
            ->getRelation($entity, 'contacts');

        if (!$contactId) {
            $relation->unrelateById($fetchedContactId);

            return;
        }

        $relation->relateById($contactId);        
    }
}

Step 4

client/custom/src/views/stock/fields/contacts.js

define(['views/fields/link-multiple-with-primary'], (Dep) => {   
    return class extends Dep {
        primaryLink = 'contact'
    }
});

Step 5

Run Rebuild.

Step 6

Execute an SQL query:

UPDATE stock
JOIN contact_stock
ON contact_stock.stock_id = stock.id AND contact_stock.deleted = 0
SET stock.contact_id = contact_stock.contact_id