Marek S. ŁukasiewiczandGitHub
f2f4937854
* Add global Lua function 'some'
Moved documentation for 'each' function to non-standard section.
* Revert "Add optional argument to template.each for empty collection output (#1359)"
This reverts commit b73dadec67.
* Reimplement #1359 using 'some' function
124 lines
3.8 KiB
Markdown
124 lines
3.8 KiB
Markdown
Lua Integrated Query (LIQ) is a SilverBullet specific Lua extension. It adds a convenient query syntax to the language in a backwards compatible way. It does so by overloading Lua’s default function call + single argument syntax when using `query` as the function call. As a result, Lua programs using LIQ are still syntactically valid Lua.
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The syntax for LIQ is `query[[my query]]`. In regular Lua `[[my query]]` is just another way of writing `"my query"` (it is an alternative string syntax). Function calls that only take a string argument can omit parentheses, therefore `query[[my query]]` is equivalent to `query("my query")`.
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However, in [[Space Lua]] it interpreted as an SQL (and [LINQ](https://learn.microsoft.com/en-us/dotnet/csharp/linq/))-inspired integrated query language.
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General syntax:
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query[[
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from <var> = <expression>
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where <expression>
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order by <expression>
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limit <expression>, <expression>
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select <expression>
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]]
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LIQ can operate on any Lua collection.
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For instance, to sort a list of numbers in descending order:
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${query[[from n = {1, 2, 3} order by n desc]]}
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However, in most cases you’ll use it in conjunction with [[API/index#index.tag(name)]]. Here’s an example querying the 3 pages that were last modified:
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${query[[
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from p = index.tag "page"
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order by p.lastModified desc
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select p.name
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limit 3
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]]}
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Note that the query returns a regular Lua table, so it can be part of a bigger expression:
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${some(query[[
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from p = index.tag "page"
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limit 0
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]]) or "Matched no pages"}
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# Clauses
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Here are the clauses that are currently supported:
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## from <expression>
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The `from` clause specifies the source of your data. There are two syntactic variants:
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With explicit variable binding:
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from v = <<expression>>
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binding each item to the variable `v`.
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And the shorter:
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from <<expression>>
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implicitly binding each item to the variable `_` as well as making all attributes directly available as variables.
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Example without variable binding:
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${query[[from {1, 2, 3} select _]]}
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With variable binding:
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${query[[from n = {1, 2, 3} select n]]}
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A more realistic example using `index.tag`:
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${query[[from index.tag "page" order by lastModified select name limit 3]]}
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## where <expression>
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The `where` clause allows you to filter data. When the expression evaluated to a truthy value, the item is included in the result.
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Example:
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${query[[from {1, 2, 3, 4, 5} where _ > 2]]}
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Or to select all pages tagged with `#meta`:
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${query[[from index.tag "page" where table.includes(tags, "meta")]]}
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Or select based on name (including folder) and a [[API/string|string function]]
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${query[[from index.tag "page" where name:startsWith("Person")]]}
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## order by <expression> [desc]
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The `order by` clause allows you to sort data, when `desc` is specified it reverts the sort order.
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As an example, the last 3 modified pages:
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${query[[
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from index.tag "page"
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order by lastModified desc
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select name
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limit 3
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]]}
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Sorting of strings can be adjusted with `queryCollation` in [[^Library/Std/Config]]
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## limit <expression>[, <expression>]
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The `limit` clause allows you to limit the number of results, optionally with an offset.
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Example:
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${query[[from {1, 2, 3, 4, 5} limit 3]]}
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You can also specify an offset to skip some results:
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${query[[from {1, 2, 3, 4, 5} limit 3, 2]]}
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## select <expression>
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The `select` clause allows you to transform each item in the result set. If omitted, it defaults to returning the item itself.
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Some examples:
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Double each number:
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${query[[from {1, 2, 3} select _ * 2]]}
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Extract just the name from pages:
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${query[[from index.tag "page" select _.name limit 3]]}
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You can also return tables or other complex values:
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${query[[
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from p = index.tag "page"
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select {
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name = p.name,
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modified = p.lastModified
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}
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limit 3
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]]}
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