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Mailgun: make merge_data work with stored handlebars templates
Mailgun has two different template mechanisms and two different ways of providing substitution variables to them. Update Anymail's normalized merge_data handling to work with either (while preserving existing batch send and metadata capabilities that also use Mailgun's custom data and recipient variables parameters). Completes work started by @anstosa in #156. Closes #155.
This commit is contained in:
Mike Edmunds
GitHub
@@ -217,6 +217,13 @@ Limitations and quirks
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the message to send, so it won't be present in your Mailgun API logs or the metadata
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that is sent to tracking webhooks.)
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**Additional limitations on merge_data with template_id**
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If you are using Mailgun's stored handlebars templates (Anymail's
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:attr:`~anymail.message.AnymailMessage.template_id`), :attr:`~anymail.message.AnymailMessage.merge_data`
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cannot contain complex types or have any keys that conflict with
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:attr:`~anymail.message.AnymailMessage.metadata`. See :ref:`mailgun-template-limitations`
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below for more details.
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**merge_metadata values default to empty string**
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If you use Anymail's :attr:`~anymail.message.AnymailMessage.merge_metadata` feature,
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and you supply metadata keys for some recipients but not others, Anymail will first
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@@ -233,20 +240,43 @@ Limitations and quirks
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.. _mailgun-templates:
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Batch sending/merge
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Batch sending/merge and ESP templates
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-------------------------------------
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Mailgun supports :ref:`batch sending <batch-send>` with per-recipient
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merge data. You can refer to Mailgun "recipient variables" in your
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message subject and body, and supply the values with Anymail's
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normalized :attr:`~anymail.message.AnymailMessage.merge_data`
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and :attr:`~anymail.message.AnymailMessage.merge_global_data`
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message attributes:
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Mailgun supports :ref:`ESP stored templates <esp-stored-templates>`, on-the-fly
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templating, and :ref:`batch sending <batch-send>` with per-recipient merge data.
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.. versionchanged:: 6.2
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Added support for Mailgun's stored (handlebars) templates.
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Mailgun has two different syntaxes for substituting data into templates:
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* "Recipient variables" look like ``%recipient.name%``, and are used with on-the-fly
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templates. You can refer to a recipient variable inside a message's body, subject,
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or other message attributes defined in your Django code. See `Mailgun batch sending`_
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for more information. (Note that Mailgun's docs also sometimes refer to recipient
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variables as "template *variables*," and there are some additional predefined ones
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described in their docs.)
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* "Template *substitutions*" look like ``{{ name }}``, and can *only* be used in
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handlebars templates that are defined and stored in your Mailgun account (via
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the Mailgun dashboard or API). You refer to a stored template using Anymail's
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:attr:`~anymail.message.AnymailMessage.template_id` in your Django code.
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See `Mailgun templates`_ for more information.
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With either type of template, you supply the substitution data using Anymail's
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normalized :attr:`~anymail.message.AnymailMessage.merge_data` and
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:attr:`~anymail.message.AnymailMessage.merge_global_data` message attributes. Anymail
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will figure out the correct Mailgun API parameters to use.
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Here's an example defining an on-the-fly template that uses Mailgun recipient variables:
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.. code-block:: python
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message = EmailMessage(
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...
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from_email="shipping@example.com",
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# Use %recipient.___% syntax in subject and body:
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subject="Your order %recipient.order_no% has shipped",
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body="""Hi %recipient.name%,
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We shipped your order %recipient.order_no%
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@@ -262,15 +292,97 @@ message attributes:
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'ship_date': "May 15" # Anymail maps globals to all recipients
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}
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Mailgun does not natively support global merge data. Anymail emulates
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the capability by copying any `merge_global_data` values to each
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recipient's section in Mailgun's "recipient-variables" API parameter.
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And here's an example that uses the same data with a stored template, which could refer
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to ``{{ name }}``, ``{{ order_no }}``, and ``{{ ship_date }}`` in its definition:
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.. code-block:: python
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message = EmailMessage(
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from_email="shipping@example.com",
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# The message body and html_body come from from the stored template.
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# (You can still use %recipient.___% fields in the subject:)
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subject="Your order %recipient.order_no% has shipped",
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to=["alice@example.com", "Bob <bob@example.com>"]
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)
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message.template_id = 'shipping-notification' # name of template in our account
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# The substitution data is exactly the same as in the previous example:
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message.merge_data = {
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'alice@example.com': {'name': "Alice", 'order_no': "12345"},
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'bob@example.com': {'name': "Bob", 'order_no': "54321"},
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}
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message.merge_global_data = {
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'ship_date': "May 15" # Anymail maps globals to all recipients
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}
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When you supply per-recipient :attr:`~anymail.message.AnymailMessage.merge_data`,
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Anymail supplies Mailgun's ``recipient-variables`` parameter, which puts Mailgun
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in batch sending mode so that each "to" recipient sees only their own email address.
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(Any cc's or bcc's will be duplicated for *every* to-recipient.)
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If you want to use batch sending with a regular message (without a template), set
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merge data to an empty dict: `message.merge_data = {}`.
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Mailgun does not natively support global merge data. Anymail emulates
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the capability by copying any :attr:`~anymail.message.AnymailMessage.merge_global_data`
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values to every recipient.
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.. _mailgun-template-limitations:
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Limitations with stored handlebars templates
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Although Anymail tries to insulate you from Mailgun's relatively complicated API
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parameters for template substitutions in batch sends, there are two cases it can't
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handle. These *only* apply to stored handlebars templates (when you've set Anymail's
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:attr:`~anymail.message.AnymailMessage.template_id` attribute).
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First, metadata and template merge data substitutions use the same underlying
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"custom data" API parameters when a handlebars template is used. If you have any
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duplicate keys between your tracking metadata
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(:attr:`~anymail.message.AnymailMessage.metadata`/:attr:`~anymail.message.AnymailMessage.merge_metadata`)
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and your template merge data
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(:attr:`~anymail.message.AnymailMessage.merge_data`/:attr:`~anymail.message.AnymailMessage.merge_global_data`),
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Anymail will raise an :exc:`~anymail.exceptions.AnymailUnsupportedFeature` error.
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Second, Mailgun's API does not allow complex data types like lists or dicts to be
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passed as template substitutions for a batch send (confirmed with Mailgun support
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8/2019). Your Anymail :attr:`~anymail.message.AnymailMessage.merge_data` and
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:attr:`~anymail.message.AnymailMessage.merge_global_data` should only use simple
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types like string or number. This means you cannot use the handlebars ``{{#each item}}``
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block helper or dotted field notation like ``{{object.field}}`` with data passed
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through Anymail's normalized merge data attributes.
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Most ESPs do not support complex merge data types, so trying to do that is not recommended
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anyway, for portability reasons. But if you *do* want to pass complex types to Mailgun
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handlebars templates, and you're only sending to one recipient at a time, here's a
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(non-portable!) workaround:
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.. code-block:: python
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# Using complex substitutions with Mailgun handlebars templates.
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# This works only for a single recipient, and is not at all portable between ESPs.
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message = EmailMessage(
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from_email="shipping@example.com",
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to=["alice@example.com"] # single recipient *only* (no batch send)
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subject="Your order has shipped", # recipient variables *not* available
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)
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message.template_id = 'shipping-notification' # name of template in our account
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substitutions = {
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'items': [ # complex substitution data
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{'product': "Anvil", 'quantity': 1},
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{'product': "Tacks", 'quantity': 100},
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],
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'ship_date': "May 15",
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}
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# Do *not* set Anymail's message.merge_data, merge_global_data, or merge_metadata.
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# Instead add Mailgun custom variables directly:
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message.extra_headers['X-Mailgun-Variables'] = json.dumps(substitutions)
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See the `Mailgun batch sending`_ docs for more information.
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.. _Mailgun batch sending:
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https://documentation.mailgun.com/user_manual.html#batch-sending
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https://documentation.mailgun.com/en/latest/user_manual.html#batch-sending
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.. _Mailgun templates:
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https://documentation.mailgun.com/en/latest/user_manual.html#templates
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.. _mailgun-webhooks:
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