code: def validateField(self, field) :
          
          if field not in self.validators and not self.collection._validation['allow_foreign_fields'] :
              raise SchemaViolation(self.collection.__class__, field)
  
          if field in self.store:
              if isinstance(self.store[field], DocumentStore) :
                  return self[field].validate()
              
              if field in self.patchStore :
                  return self.validators[field].validate(self.patchStore[field])
              else :
                  try :
                      return self.validators[field].validate(self.store[field])
                  except ValidationError as e:
                      raise ValidationError( "'%s' -> %s" % ( field, str(e)) )
                  except AttributeError:
                      if isinstance(self.validators[field], dict) and not isinstance(self.store[field], dict) :
                          raise ValueError("Validator expected a sub document for field '%s', got '%s' instead" % (field, self.store[field]) )
                      else :
                          raise
          return True
docs: Validatie a field