where

将以下英文翻译为中文：

where

https://gohugo.io/functions/where/

Filters an array to only the elements containing a matching value for a given field.

语法

where COLLECTION KEY [OPERATOR] MATCH

where filters an array to only the elements containing a matching value for a given field.

It works in a similar manner to the where keyword in SQL.

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{{ range where .Pages "Section" "foo" }}
  {{ .Content }}
{{ end }}

It can be used by dot-chaining the second argument to refer to a nested element of a value.

content/example.md

=== “yaml”

``` yaml
---
series: golang
title: Example
---
```

=== “toml”

``` toml
+++
series = 'golang'
title = 'Example'
+++
```

=== “json”

``` json
{
   "series": "golang",
   "title": "Example"
}
```

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{{ range where .Site.Pages "Params.series" "golang" }}
   {{ .Content }}
{{ end }}

It can also be used with the logical operators !=, >=, in, etc. Without an operator, where compares a given field with a matching value equivalent to =.

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{{ range where .Pages "Section" "!=" "foo" }}
   {{ .Content }}
{{ end }}

The following logical operators are available with where:

• =, ==, eq

  true if a given field value equals a matching value

• !=, <>, ne

  true if a given field value doesn’t equal a matching value

• >=, ge

  true if a given field value is greater than or equal to a matching value

• >, gt

  true if a given field value is greater than a matching value

• <=, le

  true if a given field value is lesser than or equal to a matching value

• <, lt

  true if a given field value is lesser than a matching value

• in

  true if a given field value is included in a matching value; a matching value must be an array or a slice

• not in

  true if a given field value isn’t included in a matching value; a matching value must be an array or a slice

• intersect

  true if a given field value that is a slice/array of strings or integers contains elements in common with the matching value; it follows the same rules as the intersect function.

Use where with Booleans

When using booleans you should not put quotation marks.

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{{ range where .Pages "Draft" true }}
        <p>{{ .Title }}</p>
{{ end }}

Use where with intersect

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{{ range where .Site.Pages "Params.tags" "intersect" .Params.tags }}
  {{ if ne .Permalink $.Permalink }}
    {{ .Render "summary" }}
  {{ end }}
{{ end }}

You can also put the returned value of the where clauses into a variable:

where-intersect-variables.html

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{{ $v1 := where .Site.Pages "Params.a" "v1" }}
{{ $v2 := where .Site.Pages "Params.b" "v2" }}
{{ $filtered := $v1 | intersect $v2 }}
{{ range $filtered }}
{{ end }}

Use where with first

Using first and where together can be very powerful. Below snippet gets a list of posts only from main sections, sorts it using the default ordering for lists (i.e., weight => date), and then ranges through only the first 5 posts in that list:

first-and-where-together.html

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{{ range first 5 (where site.RegularPages "Type" "in" site.Params.mainSections) }}
   {{ .Content }}
{{ end }}

Nest where Clauses

You can also nest where clauses to drill down on lists of content by more than one parameter. The following first grabs all pages in the “blog” section and then ranges through the result of the first where clause and finds all pages that are not featured:

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{{ range where (where .Pages "Section" "blog" ) "Params.featured" "!=" true }}

Unset Fields

Filtering only works for set fields. To check whether a field is set or exists, you can use the operand nil.

This can be useful to filter a small amount of pages from a large pool. Instead of setting a field on all pages, you can set that field on required pages only.

Only the following operators are available for nil

• =, ==, eq: True if the given field is not set.
• !=, <>, ne: True if the given field is set.

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{{ range where .Pages "Params.specialpost" "!=" nil }}
   {{ .Content }}
{{ end }}

Portable where filters – site.Params.mainSections

This is especially important for themes.

To list the most relevant pages on the front page or similar, you should use the site.Params.mainSections list instead of comparing section names to hard-coded values like "posts" or "post".

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{{ $pages := where site.RegularPages "Type" "in" site.Params.mainSections }}

If the user has not set this config parameter in their site config, it will default to the section with the most pages.

The user can override the default:

config.

=== “yaml”

``` yaml
params:
  mainSections:
  - blog
  - docs
```

=== “toml”

``` toml
[params]
  mainSections = ['blog', 'docs']
```

=== “json”

``` json
{
   "params": {
      "mainSections": [
         "blog",
         "docs"
      ]
   }
}
```