how to relate tables in laravel?

hi I have a problem to relate tables in laravel, I do not know how to show invoice, config tables in a view. I just need to show the data that is in those tables.

<?php

namespace App\Repositories;

use App\Invoice;
use App\InvoiceItem;
use DB;

class InvoiceRepository {
    private $model;

    public function __construct(){
        $this->model = new Invoice();
    }

    public function get($id) {
        return $this->model->find($id);
    }

    public function getAll() {
        return $this->model->orderBy('id', 'desc')->get();
    }

    public function save($data) {
        $return = (object)['response' => false];

        try {
            DB::beginTransaction();

            $this->model->iva = $data->iva;
            $this->model->subTotal = $data->subTotal;
            $this->model->total = $data->total;
            $this->model->client_id = $data->client_id;


            $this->model->save();

            $detail = [];
            foreach($data->detail as $d) {
                $obj = new InvoiceItem;

                $obj->product_id = $d->product_id;
                $obj->quantity = $d->quantity;
                $obj->unitPrice = $d->unitPrice;
                $obj->total = $d->total;

                $detail[] = $obj;
            }

            $this->model->detail()->saveMany($detail);
            $return->response = true;

            DB::commit();
        } catch (\Exception $e){
            DB::rollBack();
        }

        return json_encode($return);
    }

model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Invoice extends Model {
    public function detail(){
        return $this->hasMany('App\InvoiceItem');
    }
    public function config(){
        return $this->belongsTo('App\Config');
    }

    public function client(){
        return $this->belongsTo('App\Client');
    }
    public function scopeSearch($query, $data){
      $name= $data->name;

      return $query->where('name', 'LIKE', "%$name%");
    }
}

controller

<?php

namespace App\Http\Controllers;

use App\Repositories\ProductRepository;
use Illuminate\Http\Request,
    App\Repositories\ClientRepository,
    App\Repositories\InvoiceRepository,
    App\Http\Requests,
    PDF;

class InvoiceController extends Controller
{
    private $_clientRepo;
    private $_productRepo;
    private $_invoiceRepo;

    public function __CONSTRUCT(
        ClientRepository $clientRepo,
        ProductRepository $productRepo,
        InvoiceRepository $invoiceRepo
    )
    {
        $this->_clientRepo = $clientRepo;
        $this->_productRepo = $productRepo;
        $this->_invoiceRepo = $invoiceRepo;
    }

    public function index()
    {

        return view('invoice.index', ['model' => $this->_invoiceRepo->getAll()
            ]
        );
    }

    public function detail($id)
    {
        return view('invoice.detail', ['model' => $this->_invoiceRepo->get($id)
        ]);
    }


    public function pdf($id)
    {
        $model = $this->_invoiceRepo->get($id);

        $invoice_name = sprintf('comprobante-%s.pdf', str_pad ($model->id, 7, '0', STR_PAD_LEFT));

        $pdf = PDF::loadView('invoice.pdf', ['model' => $model
        ]);

        return $pdf->download($invoice_name);
    }

    public function add()
    {
        return view('invoice.add');
    }

    public function save(Request $req)
    {
        $data = (object)[
            'iva' => $req->input('iva'),
            'subTotal' => $req->input('subTotal'),
            'total' => $req->input('total'),
            'client_id' => $req->input('client_id'),
            'detail' => []
        ];

        foreach($req->input('detail') as $d){
            $data->detail[] = (object)[
                'product_id' => $d['id'],
                'quantity'   => $d['quantity'],
                'unitPrice'  => $d['price'],
                'total'      => $d['total']
            ];
        }

        return $this->_invoiceRepo->save($data);
    }



    public function findClient(Request $req)
    {
        return $this->_clientRepo
                    ->findByName($req->input('q'));
    }

    public function findProduct(Request $req)
    {
        return $this->_productRepo
                    ->findByName($req->input('q'));
    }
}

migration

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class Initalization extends Migration
{
    public function up()
    {
        Schema::create('clients', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('ruc');
            $table->string('address');
            $table->timestamps();
        });

        Schema::create('products', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->decimal('price', 10, 2);
            $table->timestamps();
        });

        Schema::create('invoices', function (Blueprint $table) {
            $table->increments('id');
            $table->decimal('iva', 10,2);
            $table->decimal('subTotal', 10,2);
            $table->decimal('total', 10,2);
            $table->timestamps();
        });

        Schema::create('invoice_items', function (Blueprint $table) {
            $table->decimal('quantity', 10,2);
            $table->decimal('unitPrice', 10,2);
            $table->decimal('total', 10,2);
            $table->timestamps();
        });
        Schema::create('config', function (Blueprint $table) {
            $table->increments ('id');
            $table->string('nombre');
            $table->integer('telefono');
            $table->string('email');
            $table->integer('IVA');
            $table->string('direccion');
            $table->string('ciudad');
            $table->timestamps();
        });

        // Foreign keys
        Schema::table('invoices', function ($table) {
            $table->integer('client_id')->unsigned();
            $table->foreign('client_id')->references('id')->on('clients');
//            $table->integer('config_id')->unsigned();
//            $table->foreign('config_id')->references('id')->on('config');
        });

        Schema::table('invoice_items', function ($table) {
            $table->integer('invoice_id')->unsigned();
            $table->integer('product_id')->unsigned();


            $table->foreign('invoice_id')->references('id')->on('invoices');
            $table->foreign('product_id')->references('id')->on('products');

        });

view

    <html><head>
        <style>
            .header{background:#eee;color:#444;border-bottom:1px solid #ddd;padding:10px;}

            .client-detail{background:#ddd;padding:10px;}
            .client-detail th{text-align:left;}

            .items{border-spacing:0;}
            .items thead{background:#ddd;}
            .items tbody{background:#eee;}
            .items tfoot{background:#ddd;}
            .items th{padding:10px;}
            .items td{padding:10px;}

            .silver{
    background:white;
    padding: 3px 4px 3px;
}

            h1 small{display:block;font-size:16px;color:#888;}

            table{width:100%;}
            .text-right{text-align:right;}
        </style>

    </head><body>

    <div class="header" align="center">
        <h1>
            Factura N° {{ str_pad ($model->id, 7, '0', STR_PAD_LEFT) }}
        </h1>
    </div>
    <table class="client-detail" border="1">
        <tr>
            <th style="width:100px;" >
                Cliente
            </th>
            <td align="center">{{ $model->client->name }}</td>
        </tr>
        <tr>
            <th>Ruc</th>
            <td align="center">{{ $model->client->ruc }}</td>
        </tr>
        <tr>
            <th>Dirección</th>
            <td align="center">{{ $model->client->address }}</td>
        </tr>
        <tr>
            <th>Dirección</th>
            <td align="center">{{ $model->config->nombre }}</td>
        </tr>


    </table>

    <hr/><table class="items" border="1">
            <tr>
                <th class="text-left">Producto</th>
                <th class="text-right" style="width:100px;">Cantidad</th>
                <th class="text-right" style="width:100px;">Precio Unidad</th>
                <th class="text-right" style="width:100px;">Total</th>
            </tr>

        @foreach($model->detail as $d)
            <tr>
                <td>{{$d->product->name}}</td>
                <td class="text-right">{{$d->quantity}}</td>
                <td class="text-right">$ {{number_format($d->unitPrice, 2)}}</td>
                <td class="text-right">$ {{number_format($d->total, 2)}}</td>
            </tr>
        @endforeach
        <tr>
            <th>nombre empresa</th>
        </tr>
        @foreach($model->config as $e)
            <tr>
                <td>{{$e->nombre}}</td>

        @endforeach
        <tfoot>
        <tr>
            <td colspan="3" class="text-right"><b>IVA</b></td>
            <td class="text-right">$ {{ number_format($model->iva, 2) }}</td>
        </tr>
        <tr>
            <td colspan="3" class="text-right"><b>Sub Total</b></td>
            <td class="text-right">$ {{ number_format($model->subTotal, 2) }}</td>
        </tr>
        <tr>
            <td colspan="3" class="text-right"><b>Total</b></td>
            <td class="text-right">$ {{ number_format($model->total, 2) }}</td>
        </tr>
        </tfoot></table>
    </body></html>