title: django model field get default value of the id field
body: <p>Hello guys I want to display labes for a layer in the map from geoserver but geoserver doesn't allow me to display the id field as a label. I created a new value no_man and would like for this field to automatically get the value of the id. If there is a way to display the id label I would remove the no_man, otherwise I would like to populate this field with the value of the id.</p>
  
  <p>models.py </p>
  
  <pre><code>class ww_manholes(models.Model):
      id = models.BigIntegerField(primary_key=True)
      no_man = models.BigIntegerField()
      l_ass_obj = models.BigIntegerField()
      l_field_re = models.BigIntegerField()
      street = models.BigIntegerField()
      zip_code = models.BigIntegerField()
      regio_code = models.BigIntegerField()
      owner = models.BigIntegerField()
      ww_type = models.BigIntegerField()
      accuracy = models.BigIntegerField()
      x = models.FloatField()
      y = models.FloatField()
      x_ge = models.FloatField()
      y_ge = models.FloatField()
      z = models.FloatField()
      invert_el = models.FloatField()
      inv_start = models.FloatField()
      inv_end = models.FloatField()
      depth = models.FloatField()
      depth_star = models.FloatField()
      depth_end = models.FloatField()
      material = models.BigIntegerField()
      lining = models.BigIntegerField()
      coating = models.BigIntegerField()
      contractor = models.BigIntegerField()
      const_year = models.BigIntegerField()
      diam_nom = models.BigIntegerField()
      diam_inner = models.BigIntegerField()
      joint_type = models.BigIntegerField()
      cover_dim = models.BigIntegerField()
      cover_mat = models.BigIntegerField()
      access = models.BigIntegerField()
      rough_coef = models.FloatField()
      slope = models.FloatField()
      type = models.BigIntegerField()
      sc_condit = models.BigIntegerField()
      sc_perform = models.BigIntegerField()
      sc_fail_pr = models.BigIntegerField()
      sc_fin_imp = models.BigIntegerField()
      sc_soc_imp = models.BigIntegerField()
      sc_leg_imp = models.BigIntegerField()
      sc_env_imp = models.BigIntegerField()
      sc_red_sl = models.BigIntegerField()
      sc_imp_ph = models.BigIntegerField()
      sc_imp_rep = models.BigIntegerField()
      sc_rep_cos = models.BigIntegerField()
      sc_co_fail = models.BigIntegerField()
      l_picture = models.CharField(max_length=254)
      l_drawing = models.CharField(max_length=254)
      key_om = models.FloatField()
      comments = models.CharField(max_length=254)
      geom = models.MultiPointField(srid=7392)
  
      def __unicode__(self):
          return self.id
  </code></pre>