Laravel Eloquent Composite Primary Key Relationships - laravel

Question

I have the following schema:
Schema::create('companies', function (Blueprint $table) {
$table->increments('id');
$table->string('name')->unique();
$table->timestamps();
});
Schema::create('departments', function (Blueprint $table) {
$table->increments('id');
$table->integer('company_id');
$table->string('name');
$table->timestamps();
$table->foreign('company_id')->references('id')->on('companies');
$table->unique(['company_id','name']);
});
Schema::create('employees', function (Blueprint $table) {
$table->increments('id');
$table->integer('company_id');
$table->string('name');
$table->timestamps();
$table->foreign('company_id')->references('id')->on('companies');
});
Schema::create('managed_departments', function (Blueprint $table) {
$table->integer('company_id');
$table->integer('department_id');
$table->integer('manager_id');
$table->timestamps();
$table->primary(['company_id','department_id']);
// Overlapping foreign keys guarantee that the manager
// and the department belong to the same company.
$table->foreign(['company_id','department_id'])
->references(['company_id','department_id'])
->on('departments');
$table->foreign(['company_id','manager_id'])
->references(['company_id','id'])
->on('employees');
});
Schema::create('department_staff', function (Blueprint $table) {
$table->integer('company_id');
$table->integer('department_id');
$table->integer('employee_id');
$table->timestamps();
$table->primary(['company_id','department_id', 'employee_id']);
// Overlapping foreign keys guarantees that the employee and the
// managed department belong to the same company.
$table->foreign(['company_id','department_id'])
->references(['company_id','department_id'])
->on('managed_departments');
$table->foreign(['company_id','employee_id'])
->references(['company_id','id'])
->on('employees');
});
Whats the correct model relationship between the departments, managed_departments and the department_staff tables in the
above schema - i'm a bit confused with how to define the relationship when there are composite primary keys and the following doesn't look right to me and how will eloquent know the correct foreign keys?
class Department extends Model
{
// a department is managed by an employee
public function managedDepartment
{
$this->hasOne(app\ManagedDepartment)
}
}
class ManagedDepartment extends Model
{
// a managed department belongs to department
public function Department
{
$this->belongsTo(app\Department)
}
// a managed department is managed by an employee
public function Employee
{
$this->belongsTo(app\Employee)
}
}
class DepartmentStaff extends Model
{
public function employee()
{
return $this->belongsTo('App\Employee');
}
}
class Employee extends Model
{
// an employee can managed many depts
public function managedDepartment
{
$this->hasMany(app\ManagedDepartment)
}
// an employee is asigned to one department
public function departmentStaff()
{
return $this->hasOne('App\DepartmentStaff');
}
}