Symfony2 : create a tasks form based on dynamic parameters from db

I have a Task entity which contains a list of tasks with code and description properties :

/**
 * Task
 *
 * @ORM\Table(name="tasks")
 * @ORM\Entity(repositoryClass="Foo\BarBundle\Entity\TaskRepository")
 */
class Task
{
    /**
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(name="code", type="string", length=50)
     */
    private $code;

    /**
     * @ORM\Column(name="description", type="string", length=255)
     */
    private $description;

    // ...
}

I will wish that my users enter each week the time they passed on each task. I think the best is to create another entity, Activity for example, with a task property :

/**
 * Activity
 *
 * @ORM\Table(name="activities")
 * @ORM\Entity(repositoryClass="Foo\BarBundle\Entity\ActivityRepository")
 */
class Activity
{
    /**
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(name="date", type="datetime")
     */
    private $date;

    /**
     * @ORM\Column(name="duration", type="smallint")
     */
     private $duration;

    /**
     * @ORM\ManyToOne(targetEntity="Task", inversedBy="activities") // with activities property in Task entity
     * @ORM\JoinColumn(name="task_id", referencedColumnName="id")
     */
    private $task;

     // ...
}

But obviously the form displays the activity fields with a select form containing all the Tasks...

What is the best way to have all my tasks displayed in a single page, with the possibility to enter a value for each of them by week please ? (the week is given by a GET parameter).

Edit

A similar question with an answer which helped me can be found here.