如何保存多对多关系？

Question

I am creating the backoffice for a website I'm developing with Laravel4. So far so good, but I got into this error when trying to save a model (components) that has a belongsToMany relationship with another model (codes).

I am getting this error:

SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'component_id' cannot be null (SQL: insert into `component_codes` (`code_id`, `component_id`) values (4, ))

Here's my create blade template:

@foreach ($codes as $code)
    <tr>
        <td>{{ $code->id }}</td>
        <td>{{ $code->code }}</td>
        <td>{{ $code->packing }}</td>
        <td>@if ($code->active == 1) <span class="label label-success">Active</span> @else <span class="label label-secondary">Inactive</span> @endif</td>
        <td><input type="checkbox" name="code_checkbox[]" value="{{ $code->id }}" /></td>
    </tr>   
@endforeach

And my store function:

$component            = new PackbuilderComponent;
$component->name_en   = Input::get('name_en');
$component->filter_id = Input::get('filter_id');
$component->image     = $fullpath;
$component->thumb     = $fullthumbpath;
$component->codes()->sync(Input::get('code_checkbox'));
$component->save();

I don't get it. Isn't it supposed to know the ID of the component it's creating and simply associate the "code_id" to the pivot table? Why is it asking for a "component_id" that doesn't even exist yet?

Answer 1

When working with the pivot table, both models on either side of the relationship need to already exist in your database.

All you need to do is save the $component model to your database first, then you can attach or sync relationships to it.

Change the following;

$component->codes()->sync(Input::get('code_checkbox'));
$component->save();

To;

$component->save();
$component->codes()->sync(Input::get('code_checkbox'));