使用Gmail SDK：无需重新生成raw字段能否设置草稿主题？

Great question! I’ve worked with the Gmail API quite a bit, so let’s break this down in a way that’s easy to implement.

Do you need to regenerate the raw field to update the draft subject? #

Absolutely not. The Gmail API lets you modify specific parts of a draft (like the subject) without rebuilding the entire MIME message stored in the raw field. Instead, you can directly edit the draft’s payload structure—specifically the email headers.

When you fetch a draft via drafts.get, the response includes a message.payload.headers array holding all email headers (Subject, From, To, etc.). You just need to find the Subject entry in this list, update its value, and send that modified header set back to the API.

Can you use PUT or PATCH methods? #

Both are supported, but PATCH is the smarter choice here:

• drafts.update (PUT method): This expects a full draft resource (or a valid message structure) to replace the existing draft. While you can use this by passing the modified payload headers plus the rest of the draft data, it’s inefficient—you’re sending way more data than necessary.
• drafts.patch (PATCH method): Built for partial updates, you only need to send the specific fields you want to change. No need to include the entire draft, making this far cleaner and more efficient for updating just the subject.

Example Workflow (Python SDK) #

Here’s a quick code snippet to walk you through the process:

1. Fetch the existing draft

# Retrieve the draft from Gmail
draft = service.users().drafts().get(userId='me', id=draft_id).execute()

2. Update the Subject header

# Locate and modify the Subject header in the payload
headers = draft['message']['payload']['headers']
for header in headers:
    if header['name'].lower() == 'subject':
        header['value'] = 'My Updated Draft Subject'
        break
# Fallback: add a Subject header if it doesn't exist (rare for drafts)
else:
    headers.append({'name': 'Subject', 'value': 'My Updated Draft Subject'})

3. Patch the draft with the updated header

# Send the partial update using PATCH
updated_draft = service.users().drafts().patch(
    userId='me',
    id=draft_id,
    body={'message': {'payload': {'headers': headers}}}
).execute()

Quick Notes #

• Remember to target the message.payload.headers within the draft object—drafts wrap a message resource, so that’s where the headers live.
• If you’re using a different language SDK, the pattern stays the same: fetch the draft, update the Subject header in the payload, then send the partial update via patch.

内容的提问来源于stack exchange，提问作者Oleh Yatskiv