自定义WagtailAdminPageForm的save方法多次触发，如何仅在页面保存时执行一次？

需求 #

• 在Wagtail页面保存时，根据编辑器填写的字段自动生成另一个字段内容。

现有实现 #

按照Wagtail官方文档自定义WagtailAdminPageForm，在save方法中添加字段生成逻辑，代码如下：

from wagtail.models import Page
from wagtail.admin.forms import WagtailAdminPageForm

class TestPageForm(WagtailAdminPageForm):
    def clean(self):
        cleaned_data = super().clean()
        print("-> called TestPageForm.clean()")
        return cleaned_data

    def save(self, commit=True):
        print(f"1 {commit=}")
        page = super().save(commit=False)
        print(f"2 {commit=}")
        print("-> called TestPageForm.save()")
        # 处理逻辑，将结果保存到实例字段，例如：
        # page.pdf_cover_image = get_cover_image(self.cleaned_data["pdf"])

        if commit:
            print(f"{commit=}: calling page.save()")
            page.save()

        return page


class TestPage(Page):
    base_form_class = TestPageForm

遇到的问题 #

clean()和save()方法会被多次调用（包括页面加载、预览场景），且commit参数始终为False，无法区分是否为真正的页面保存操作，希望自定义保存操作仅在页面保存时执行一次。

日志情况 #

编辑页面时的调用记录 #

[10/May/2023 10:35:37] "GET /admin/pages/139/edit/ HTTP/1.1" 200 71082
[...assets...]
-> called TestPageForm.clean()
1 commit=False
2 commit=False
-> called TestPageForm.save()
[10/May/2023 10:35:37] "GET /admin/pages/139/edit/preview/?in_preview_panel=true&mode= HTTP/1.1" 200 0
[10/May/2023 10:35:37] "DELETE /admin/pages/139/edit/preview/ HTTP/1.1" 200 17
-> called TestPageForm.clean()
[10/May/2023 10:35:37] "POST /admin/pages/139/edit/preview/ HTTP/1.1" 200 40
-> called TestPageForm.clean()
1 commit=False
-> called TestPageForm.clean()
2 commit=False
-> called TestPageForm.save()
1 commit=False
2 commit=False
-> called TestPageForm.save()
[10/May/2023 10:35:37] "GET /admin/pages/139/edit/preview/?in_preview_panel=true&mode= HTTP/1.1" 200 0

保存页面时的调用记录 #

[10/May/2023 10:35:37] "GET /admin/pages/139/edit/preview/?in_preview_panel=true&mode= HTTP/1.1" 200 0
-> called TestPageForm.clean()
1 commit=False
2 commit=False
-> called TestPageForm.save()
[10/May/2023 10:38:10] "POST /admin/pages/139/edit/ HTTP/1.1" 302 0
[10/May/2023 10:38:10] "GET /admin/pages/8/ HTTP/1.1" 200 45356

内容的提问来源于stack exchange，提问作者tombreit