79 lines
2.9 KiB
Markdown
79 lines
2.9 KiB
Markdown
The syntax of queries is inspired by [SQL](https://en.wikipedia.org/wiki/SQL). It can be used using [[Live Queries]] as well as via nested queries part of template expressions: [[Expression Language#Queries]].
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Let’s start with a query that demonstrates some of the supported clauses. Hover over the result and click the edit icon to show the code that generates the view:
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```query
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page
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order by lastModified desc
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where size > 100
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select name
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limit 10
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render [[Library/Core/Query/Page]]
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```
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It’s most convenient to use the `/query` [[Snippets|snippet]] to insert a query in a page.
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A query is formulated specifying a `querySource` followed by a number of clauses that modify or restrict the result set. If you haven’t already, check out how [[Objects]] work in SilverBullet.
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Every time `<expression>` is referenced here, an expression using the [[Expression Language]] can be used.
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# Clauses
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## where <expression>
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A `where` clause filters out all objects that do not match a certain condition. You can have multiple `where` clauses if you like, which will have the same effect as combining them with the `and` keyword.
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Here is a simple example based on a custom tag `#person` (see [[Objects]] on how this works):
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```#person
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name: John
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age: 7
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---
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name: Pete
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age: 25
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```
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To query all `person`s that are above age 21, we can use the following `where` clause:
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```query
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person where page = @page.name and age > 21
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```
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## order by <expression>
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To sort results, an `order by` clause can be used, optionally with `desc` to order in descending order (ascending is the default):
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```query
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person where page = @page.name order by age desc
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```
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## limit <expression>
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To limit the number of results, you can use a `limit` clause:
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```query
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person where page = @page.name limit 1
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```
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## select
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You can use the `select` clause to select only specific attributes from the result set. You can use it either simply as `select attribute1, attribute2` but also select the value of certain expressions and give them a name, even one containing spaces using the backtick identifier syntax:
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```query
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person
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where page = @page.name
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select name, age, age + 1 as `next year`
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```
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## render each <template> and render all <template>
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In the context of [[Live Queries]], by default, results are rendered as a table. To instead render results using [[Templates|a template]], use the `render` clause, which comes in two shapes `render each` where the template is instantiated for _each_ result (the `each` keyword is optional):
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```query
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person
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where page = @page.name
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render each [[internal-template/person]]
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```
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And `render all` where the entire result set is passed to the template as a list so the template can do its own iteration using `#each`, which you could then use to e.g. build a table (using this [[internal-template/people]] template, for instance):
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```query
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person
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where page = @page.name
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render all [[internal-template/people]]
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```
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