Personalizations field error when sending multiple dynamic template emails in sendgrid

Question

I'm trying to send a bulk email using Sendgrid Dynamic Templates in Django and getting this error: The personalizations field is required and must have at least one personalization.

Using sendgrid 6.9.7

Does anyone see where I might be going wrong:

from django.conf import settings
from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Mail, To

def send_mass_email():

    to_emails = [
        To(email='email1@gmail.com',
           dynamic_template_data={
              "thing_i_want_personalized": 'hello email 1',
           }),
        To(email='email2@gmail.com',
           dynamic_template_data={
              "thing_i_want_personalized": 'hello email 2',
           }),
    ]

    msg = Mail(
      from_email='notifications@mysite.com>',
    )
    msg.to_emails = to_emails
    msg.is_multiple = True
    msg.template_id = "d-template_id"

    try:
        sendgrid_client = SendGridAPIClient(settings.SENDGRID_API_KEY)
        response = sendgrid_client.send(msg)
        print(response.status_code)
        print(response.body)
        print(response.headers)
    except Exception as e:
        print(e)
        print(e.body)

    return

The output is

HTTP Error 400: Bad Request
b'{"errors":[{"message":"The personalizations field is required and must have at least one personalization.","field":"personalizations","help":"http://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/errors.html#-Personalizations-Errors"}]}'

Answer 1

The Mail class does some stuff during initialization with the initial values (it sets private internal values based on to_emails), so you need to pass to_emails and is_multiple in the initializer and not later:

from django.conf import settings
from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Mail, To

def send_mass_email():
    to_emails = [
        To(email='email1@gmail.com',
           dynamic_template_data={
              "thing_i_want_personalized": 'hello email 1',
           }),
        To(email='email2@gmail.com',
           dynamic_template_data={
              "thing_i_want_personalized": 'hello email 2',
           }),
    ]

    msg = Mail(
      from_email='notifications@mysite.com>',
      to_emails = to_emails,
      is_multiple = True
    )
    msg.template_id = "d-template_id"

    try:
        sendgrid_client = SendGridAPIClient(settings.SENDGRID_API_KEY)
        response = sendgrid_client.send(msg)
        print(response.status_code)
        print(response.body)
        print(response.headers)
    except Exception as e:
        print(e)
        print(e.body)

    return