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diff --git a/content/en/methods/page/IsDescendant.md b/content/en/methods/page/IsDescendant.md new file mode 100644 index 000000000..f1042564e --- /dev/null +++ b/content/en/methods/page/IsDescendant.md @@ -0,0 +1,99 @@ +--- +title: IsDescendant +description: Reports whether PAGE1 in a descendant of PAGE2. +categories: [] +keywords: [] +action: + related: + - methods/page/Ancestors + - methods/page/CurrentSection + - methods/page/FirstSection + - methods/page/InSection + - methods/page/IsAncestor + - methods/page/Parent + - methods/page/Sections + returnType: bool + signatures: [PAGE1.IsDescendant PAGE2] +--- + +{{% include "methods/page/_common/definition-of-section.md" %}} + +With this content structure: + +```text +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: + +```go-html-template +{{ 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: + +```go-html-template +{{ $path := "/auctions/2023-11" }} +{{ with .Site.GetPage $path }} + {{ $.IsDescendant . }} → true +{{ else }} + {{ errorf "Unable to find the section with path %s" $path }} +{{ end }} + ``` + +## Understanding context + +Inside of the `with` block, the [context] (the dot) is the section `Page` object, not the `Page` object passed into the template. If we were to use this syntax: + +```go-html-template +{{ with .Site.GetPage "/auctions" }} + {{ .IsDescendant . }} → true +{{ end }} +``` + +The result would be wrong when rendering the "auction-1" page because we are comparing the section page to itself. + +{{% note %}} +Use the `$` to get the context passed into the template. +{{% /note %}} + +```go-html-template +{{ with .Site.GetPage "/auctions" }} + {{ $.IsDescendant . }} → true +{{ end }} +``` + +{{% note %}} +Gaining a thorough understanding of context is critical for anyone writing template code. +{{% /note %}} + +[context]: /getting-started/glossary/#context +[`with`]: /functions/go-template/with +[`else`]: /functions/go-template/else |