Relations for invoices

gistfile1.txt

<?php

namespace App;

class Line extends Model
{
    protected $table = 'lines';
    
    protected $fillable = [];
    
    public function details()
    {
        return $this->belongsTo(App\InvoiceDetail::class, 'invoice_details');
    }

}

Invoice.php

<?php

namespace App;

class Invoice extends Model
{
    protected $table = 'invoices';
    
    // Don't forget to add your fillables
    protected $fillable = [];
    
    public function details()
    {
        return $this->hasMany(App\InvoiceDetail::class, 'invoice_details');
    }

}

InvoiceDetails.php

<?php

namespace App;

class InvoiceDetail extends Model
{
    protected $table = 'invoice_details';
    
    protected $fillable = [];
    
    public function invoice()
    {
        return $this->belongsTo(App\Invoice::class);
    }
    
    public function lines()
    {
        return $this->hasOne(App\Line::class);
    }

}

migrations.php

<?php 

Schema::create('invoices', function (Blueprint $table)
{
    $table->increments('id');
});

Schema::create('invoice_details', function (Blueprint $table)
{
    $table->increments('id');
    $table->integer('invoice_id')->unsigned();
});

Schema::create('lines', function (Blueprint $table) {
    $table->increments('id');
    $table->integer('invoice_details_id')->unsigned();
});

sample

$line = Line::create(['name' => 'product1']);
$invoiceDetail = InvoiceDetail::create(['field1' => 'value1']);
$invoiceDetail->line()->save($line);

$line2 = Line::create(['name' => 'product2']);
$invoiceDetail2 = InvoiceDetail::create(['field1' => 'value1']);
$invoiceDetail2->line()->save($line2);

$invoice = Invoice::create(['field1' => 'value1']);

$invoice->details()->saveMany([$invoiceDetail, $invoiceDetail2]);