Changes

This [[Module Library|XQuery Module]] contains functions for handling ''streamablelazy'' items.

In contrast to conventional standard XQuery items, streamable items may take up much less space, because they only contain a lazy item contains a reference to the actual data. The , and the data itself will only be retrieved if it is requiredrequested. Hence, possible errors will be postponed, e.g. if it needs to and no memory will be serialized or processed occupied by another expressiona lazy item as long as its content has not been requested yet.

Currently, the The following BaseX functions return streamable lazy items:

* Lazy Base64 binaries:** <code>[[Database Module#db:retrieve|db:retrieve]]</code>* * <code>[[Fetch Module#fetch:binary|fetch:binary]]</code>* [[Fetch Module#fetch:text|fetch:text]]* <code>[[File Module#file:read-binary|file:read-binary]]* [[File Module#file:read-text|file:read-text]]</code>

The following functions are capable of processing streamed input* Lazy strings:** <code>[[Fetch Module#fetch:text|fetch:text]]</code>** <code>[[File Module#file:read-text|file:read-text]]</code>

Some functions are capable of consuming the contents of lazy items in a ''streamable'' fashion: data will not be cached, but instead passed on to another target (file, the calling expression, etc.). The following streaming functions are currently available: * [[Archive Module]] (most functions)* Conversion Module: <code>[[Conversion Module#convert:binary-to-bytes|convert:binary-to-bytes]]</code>, <code>[[Conversion Module#convert:binary-to-string|convert:binary-to-string]]</code>* Database Module: <code>[[Database Module#db:store|db:store]]</code>* File Module: <code>[[Fetch File Module#file:write-textbinary|file:write-textbinary]]* </code>, <code>[[File Module#file:write-binarytext|file:write-binarytext]] </code> (if no encoding is specified)* [[Hashing Module]](all functions) The XQuery expression below serves as an example on how large files can be downloaded and written to a file with constant memory consumption: <syntaxhighlight lang="xquery">file:write-binary('output.data', fetch:binary('http://files.basex.org/xml/xmark111mb.zip'))</syntaxhighlight> If lazy items are serialized, they will be streamed as well.

All functions and errors in this module are assigned to the {{Code|<code><nowiki>http://basex.org/modules/stream}} lazy</nowiki></code> namespace, which is statically bound to the {{Code|streamlazy}} prefix.<br/>All errors are assigned to the {{Code|http://basex.org/errors}} namespace, which is statically bound to the {{Code|bxerr}} prefix.

==streamlazy:materializecache== 

| width='90120' | '''Signatures'''|{{Func|streamlazy:materializecache|$items as item ()*|item()*}}<br/>{{Func|lazy:cache|$items as item()*, $lazy as xs:boolean|item()*}}

|Returns a materialized instance Caches the data of the specified lazy {{Code|$itemitems}}.in a sequence:<br />* data of lazy items will be retrieved and cached inside the item.* non-lazy items, or lazy items with cached data, will simply be passed through.* If an item {{Code|$lazy}} is streamableset to {{Code|true()}}, its content caching will be retrieved, and a new item containing its deferred until the data is eventually requested. Streaming will be disabled: Data will always be cached before a stream is returned. OtherCaching is advisable if an item will be processed more than once, nonor if the data may not be available anymore at a later stage.|-streamable items | '''Example'''|In the following example, a file will simply be deleted before its content is returned.To avoid a “file not found” error when serializing the result, the content must be cached:<syntaxhighlight lang="xquery">let $file := 'data.txt'let $text := lazy:cache(file:read-text($file))return (file:delete($file), $text)</syntaxhighlight>

==streamlazy:is-streamablelazy== 

| width='90120' | '''Signatures'''|{{Func|streamlazy:is-streamablelazy|$item as item()|item()xs:boolean}}

|Checks if whether the specified {{Code|$item}} is streamablelazy.|} ==lazy:is-cached== {| width='100%'|-| width='120' | '''Signatures'''|{{Func|lazy:is-cached|$item as item()|xs:boolean}}|-| '''Summary'''|Checks whether the contents of the specified {{Code|$item}} are cached. The function will always return {{Code|true}} for non-lazy items.