How to fire an automatic email through Django when you receive a new value in the database?

Question

Hello, my system is monitoring a server services, when a service fails I get a new value in the database with status "8" which means error, I would like to send an email to some user stating this failure, I’ve heard of Django’s Signals, however, I have no idea how to implement this.

Follow my models.py

class Executionresults(models.Model):
    id = models.UUIDField(db_column='ID', primary_key=True)  # Field name made lowercase.
    taskid = models.UUIDField(db_column='TaskID')  # Field name made lowercase.
    executionid = models.UUIDField(db_column='ExecutionID')  # Field name made lowercase.
    appid = models.ForeignKey(Apps, on_delete=models.CASCADE, db_column='AppID')  # Field name made lowercase.
    executingnodeid = models.UUIDField(db_column='ExecutingNodeID')  # Field name made lowercase.
    status = models.IntegerField(db_column='Status')  # Field name made lowercase.
    starttime = models.DateTimeField(db_column='StartTime')  # Field name made lowercase.

Answer 1

Use Django-model-utils

pip install django-model-utils

Add a field to make tracking in its model, and overrides the method save, your class would look like this:

from model_utils import FieldTracker

class Executionresults(models.Model):
    id = models.UUIDField(db_column='ID', primary_key=True)
    taskid = models.UUIDField(db_column='TaskID')
    executionid = models.UUIDField(db_column='ExecutionID')lowercase.
    appid = models.ForeignKey(Apps, on_delete=models.CASCADE, db_column='AppID')  
    executingnodeid = models.UUIDField(db_column='ExecutingNodeID') 
    status = models.IntegerField(db_column='Status')
    starttime = models.DateTimeField(db_column='StartTime')

    # Acrescente o campo abaixo
    tracker = FieldTracker(fields=['status'])

    # Sobrescreva o metodo save 
    def save(self, *args, **kwargs):
        # Cheque se o campo foi alterado 
        if bool(self.tracker.changed()):
            # Envie o email aqui

        # Salve os dados normalmente
        uper().save(*args, **kwargs)

At the indicated point call the code for sending the email.

You can also, instead of just checking if the field has changed, compare it as the error value, in which case save would look like this:

    # Sobrescreva o metodo save 
    def save(self, *args, **kwargs):
        # Cheque se o campo recebeu o valor do erro 
        if self.tracker.changed()['status']==8:
            # Envie o email aqui

        # Salve os dados normalmente
        uper().save(*args, **kwargs)

To learn more about Fieldtrakcer, access this link.

Edited (07/03/19) [Experimental]: Superimposing the method __init__

class Executionresults(models.Model):
    # ... Definição dos campos anteriores
    status = models.IntegerField(db_column='Status')
    starttime = models.DateTimeField(db_column='StartTime')

    # Acrescente a variável abaixo
    __status_original = None

    # Sobrescreva o metodo __init__
    def __init__(self, *args, **kwargs):
        super(Executionresults, self).__init__(*args, **kwargs)
        # guarde o valor do status 
        self.__status_original = self.status

    def save(self, force_insert=False, force_update=False, *args, **kwargs):
        # Cheque se o campo foi alterado 
        if self.status != self.__status_original:
            # Envie o email aqui

        # Salve os dados 
        super(Executionresults, self).save(force_insert, force_update, *args, **kwargs)
        self.__status_original = self.status