class Customer extends Model
{
    protected $table = 'customers';

    public function contracts()
    {
        return $this->hasMany('AppContract');
    }

class Contract extends Model
{
    public function customer()
    {
        return $this->belongsTo('AppCustomer');
    }
}

$customers = Customer::with(['contracts' => function($query)
     {
        $query->where('data_end','>=','2017-07-01')
              ->where('data_end','<=','2017-07-31')
              ->where('typ','=','U') ;
     }
    ])->paginate(10);

"Customer 1"
"Customer 2"
"Customer 3"
  *"Contract 1"
  *"Contract 2"
  *"Contract 3"
"Customer 4"
  *"Contract 1"
  *"Contract 2"
  *"Contract 3"
"Customer 4"