Support for per-message meta data for SendGrid

[janneThoft]

SendGrid supports specifying the metadata per message when using the bulk-sending API, like with merge data. This is really useful in some cases, so here's simple support for it using the same kind of API as merge data.

[medmunds]

Thanks for this! It's a nice addition to Anymail. (I recall Mandrill supports something similar, and think some of the other ESPs may too.)

Code looks good. I'd like to add some tests before merging, in test_sendgrid_backend. (Basic behavior of this feature, and also checking what happens if someone wants to use both merge_data and merge_metadata on the same message.) If you'd like to take a crack at the tests, that's great, or if not I can do it later this week.

[medmunds]

Looks like the tests uncovered some issues that will need to be addressed before this can be merged.

[medmunds]

I think this entire section that merges custom_args (global metadata) is unnecessary. SendGrid supports custom_args in both individual personalizations and at the top level (globally), and merges them as expected. Also...

[janneThoft]

Are you sure about this? We could not make it work with individual custom_args.

[medmunds]

Huh. If you expand custom_args in their docs, it says "personalizations[x].custom_args will be merged with message level custom_args, overriding any conflicting keys."

SendGrid docs have certainly been known to, um, not match their actual implementation. But I just ran a quick test, and custom_args personalizations seemed to behave as documented. Is there a specific case that didn't work for you?

Here's the test I ran:

POST https://api.sendgrid.com/v3/mail/send HTTP/1.1
Authorization: Bearer {{SENDGRID_API_KEY}}
Content-Type: application/json

{
  "custom_args": {
    "common": "common value",
    "shared": "default shared value"
  },
  "personalizations": [{
    "to": [{"email": "recip+1@example.com"}],
    "subject": "Custom args test (1)",
    "custom_args": {
      "specific": "specific value 1",
      "shared": "override shared value"
    }
  }, {
    "to": [{"email": "recip+2@example.com"}],
    "subject": "Custom args test (2)",
    "custom_args": {
      "specific": "specific value 2"
    }
  }],
  "from": {"email": "test@{{SENDGRID_TEST_DOMAIN}}"},
  "content": [{
    "type": "text/plain",
    "value": "Testing handling of custom args"
  }]
}

After sending that, SendGrid's email_activity dashboard shows the expected (merged) Unique Args for each message:

recip+1:

recip+2:

[medmunds]

@janneThoft do you have any more details about what didn't work with mixing individual and top-level custom_args? They seem to be working for me.

[janneThoft]

I'm sorry, it seems we must have been making a mistake when testing then

[zak10]

I'd love to see these features land in a release soon. Down to dive in if any help is needed.

[medmunds]

I'm hoping to hear back from @janneThoft on what problem they were seeing with individual custom_args (see thread above).

[medmunds]

Released in Anymail v6.0.