[Bug] Select/Select2 Multiple cannot update a hasManyThrough relationship.

[juniorgarcia]

Bug report

What I did:

Tried to use a select2_multiple field type to update a relationship who comes from a hasManyThrough relationship.

What I expected to happen:

The pivot table should be synced with the information sent.

What happened:

I've got the error Method Illuminate\Database\Query\Builder::sync does not exist.

What I've already tried to fix it:

Nothing, since it seems that this field type try to sync a direct relationship, not a query builder type.

Backpack, Laravel, PHP, DB version:

• backpack/crud: 3.4.23
• laravel/framework: v5.6.27
• PHP 7.2.5
• MySQL 5.7.22

Example of code

// UserCrudController.php

$this->crud->addcolumn([
  'label'     => 'Subsidiary',
  'type'      => 'select2_multiple',
  'name'      => 'subsidiaryCities',
  'entity'    => 'subsidiaryCities',
  'attribute' => 'subsidiaryNameWithCityName',
  'model'     => 'App\SubsidiaryCity',
]);

// App/Models/User.php
public function subsidiaryCities()
{
    return $this->hasManyThrough(SubsidiaryCity::class,
        SubsidiaryCityUser::class, 'subsidiarycity_id', 'id', 'id',
        'user_id');
}

The query works properly, but I can't sync.

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[promatik]

Hi @juniorgarcia! Can you please give us more information about your models?

I'm asking you this because I don't believe hasManyThrough relations should have a field and be "edited".

I'll give the example on Laravel Docs regarding hasManyThrough relations.

countries
    id - integer
    name - string

users
    id - integer
    country_id - integer
    name - string

posts
    id - integer
    user_id - integer
    title - string

A user belongsTo a country, and a user hasMany posts, so;

• a country has many posts through users.
• a post has one country through the user.

To include a field type hasManyThrough the idea would be to have it on a country Model? And remove or add posts? Or have it on a post, and add or remove countries? It would be impossible because a post belongs to a user, a country can't remove the posts of their users 🤷‍♂️

@tabacitu and @pxpm what do you think about this? Am I missing any use case?

[juniorgarcia]

Hello, how are you? Well, unfortunately I'm no longer part of the project which I found this issue, hence, I have no more access to the source code nor remember about the details.

I'm sorry for that.

[tabacitu]

Thanks for the update @juniorgarcia ! It's been more than 2 years so that's understandable 🤣 😞 sorry about that.

@promatik after our meeting yesterday I think I agree with you. I don't see any use case where an admin should be able to create/edit a hasOneThrough/hasManyThrough relationship. Because that'd basically mean editing the intermediary entry. Which is OK when it's just a pivot table, but in this case, it's NOT a just pivot table, it's a real entry with meaning outside the hasOneThrough/hasManyThrough relationship - so editing it might have unintended consequences.

To rephrase, I've used hasOneThrought & hasManyThrough relationships myself, and I find them useful. But I think they're more meant to be used when READING, not CREATING or UPDATING entries... at least that's how I see it.

@pxpm you're the relationship expert here, what do you think? Do you see any use case where we should be supporting hasOneThrought / hasManyThrough? Both from the admin perspective and from the developer perspective?

[promatik]

@pxpm reminding you on this 🙌

[tabacitu]

Bump @pxpm - if you agree with @promatik and I, let's close this issue please.

[pxpm]

I will be the one giving it the last hammer!

I do agree with @promatik .

I was trying (and tried before, this is not the first time I look at this issue), to make sense from what @juniorgarcia tried to do, from what it seems at the time, the user can have many subsidiaries and it seems it would be suitable for a belongsToMany relation, and if you need a pivot model (SubcidiaryCityUser) you should be totally fine with that and not with this relation.

That said, I don't think this relations should be editable, otherwise the changes would be made at intermediary tables.