IsDescendant.md

title	description	categories	keywords	action
IsDescendant	Reports whether PAGE1 is a descendant of PAGE2.			related returnType signatures methods/page/Ancestors methods/page/CurrentSection methods/page/FirstSection methods/page/InSection methods/page/IsAncestor methods/page/Parent methods/page/Sections bool PAGE1.IsDescendant PAGE2

{{% include "methods/page/_common/definition-of-section.md" %}}

With this content structure:

content/
├── auctions/
│   ├── 2023-11/
│   │   ├── _index.md
│   │   ├── auction-1.md
│   │   └── auction-2.md
│   ├── 2023-12/
│   │   ├── _index.md
│   │   ├── auction-3.md
│   │   └── auction-4.md
│   ├── _index.md
│   ├── bidding.md
│   └── payment.md
└── _index.md

When rendering the "auctions" page:

{{ with .Site.GetPage "/" }}
  {{ $.IsDescendant . }} → true
{{ end }}

{{ with .Site.GetPage "/auctions" }}
  {{ $.IsDescendant . }} → false
{{ end }}

{{ with .Site.GetPage "/auctions/2023-11" }}
  {{ $.IsDescendant . }} → false
{{ end }}

{{ with .Site.GetPage "/auctions/2023-11/auction-2" }}
  {{ $.IsDescendant . }} → false
{{ end }}

In the examples above we are coding defensively using the with statement, returning nothing if the page does not exist. By adding an else clause we can do some error reporting:

{{ $path := "/auctions/2023-11" }}
{{ with .Site.GetPage $path }}
  {{ $.IsDescendant . }} → true
{{ else }}
  {{ errorf "Unable to find the section with path %s" $path }}
{{ end }}

Understanding context

Inside of the with block, the context (the dot) is the section Page object, not the Page object passed into the template. If we were to use this syntax:

{{ with .Site.GetPage "/auctions" }}
  {{ .IsDescendant . }} → true
{{ end }}

The result would be wrong when rendering the "auction-1" page because we are comparing the section page to itself.

{{% note %}} Use the $ to get the context passed into the template. {{% /note %}}

{{ with .Site.GetPage "/auctions" }}
  {{ $.IsDescendant . }} → true
{{ end }}

{{% note %}} Gaining a thorough understanding of context is critical for anyone writing template code. {{% /note %}}