Support for SendGrid new dynamic templates

[juliomenendez]

• Anymail version: 4.0
• ESP: SendGrid
• Versions of Django, requests, python: Django 1.11.14, requests 2.18.4, Python 3.6.6
• Exact error message and/or stack trace: SendGrid responds with a HTTP 400.

Basically the merge_data is not used on Dynamic Templates. The context for the templates now needs to be defined in personalizations.dynamic_template_data.
API documentation: https://sendgrid.com/docs/User_Guide/Transactional_Templates/how_to_send_an_email_with_transactional_templates.html#-Send-a-transactional-email
sendgrid-python example: https://github.com/sendgrid/sendgrid-python/blob/master/use_cases/transational_templates.md

[medmunds]

Wow, the new dynamic templates seem much cleaner and simpler than the legacy templates-substitutions-sections approach. (And no more need to define your own template substitution delimiters—it's just handlebars.)

Looks like SendGrid announced "dynamic templates" on their blog about a month ago, and hasn't yet updated their v3 /mail/send reference docs to cover the new params. (The reference for dynamic template sends is weirdly on a different, non-SendGrid domain: https://dynamic-templates.api-docs.io/3.0/mail-send-with-dynamic-transactional-templates/v3-mail-send. And those docs don't include the legacy template params, which is not exactly comforting for API backwards compatibility.)

Dynamic template IDs seem to start with "d-" (with a hyphen), and legacy IDs don't, so Anymail could probably use this to switch between the two API param formats. This isn't documented anywhere, so probably should also have a fallback Anymail option in case this heuristic isn't always right.

Unfortunately, it's not possible to use Anymail's esp_extra to work get to this feature in the meantime, because SendGrid's dynamic_template_data param needs to end up inside each individual personalizations[] array entry (and esp_extra is just merged in at the root of the /mail/send payload). Should find a way to allow personalizations mods from esp_extra, to cover any future SendGrid feature additions.

[juliomenendez]

I actually got it working just like that, checking if the template ID starts with d- and adding a dictionary like this to esp_extra:

message.esp_extra = {
    'personalizations': [{
        'to': [{
            'email': to_email,
        },],
        'dynamic_template_data': {
            ...  # context for the email template
        },
    },],
}

[medmunds]

Oh, yeah, cool... that definitely works.

I'm unhappy that Anymail is making you re-create the entire personalizations block in esp_extra, which means you have to repeat the message's to (and any other personalizations data that Anymail would normally populate from the message, including things like SendGrid display-name bug workarounds). But I'm glad you found a way to get it working until Anymail can be updated.

[medmunds]

SendGrid dynamic template support is released in Anymail v4.1.

[juliomenendez]

Awesome, thanks!