Difference between revisions of "Lazy Module"
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The following BaseX functions return streamable items: | The following BaseX functions return streamable items: | ||
| − | * <code>[[Database Module#db:retrieve|db:retrieve]]</code> | + | * Streamable Base64 binaries: |
| − | * <code>[[Fetch Module#fetch:binary|fetch:binary]]</code> | + | ** <code>[[Database Module#db:retrieve|db:retrieve]]</code> |
| − | * <code>[[ | + | ** <code>[[Fetch Module#fetch:binary|fetch:binary]]</code> |
| − | * <code>[[ | + | ** <code>[[File Module#file:read-binary|file:read-binary]]</code> |
| − | * <code>[[File Module#file:read-text|file:read-text]]</code> | + | |
| + | * Streamable 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 items in a ''streamable'' fashion: data will never be cached, but instead passed on to another target (file, the calling expression, etc.). The following streaming functions are currently available: | Some functions are capable of consuming items in a ''streamable'' fashion: data will never be cached, but instead passed on to another target (file, the calling expression, etc.). The following streaming functions are currently available: | ||
Revision as of 22:55, 12 March 2013
This XQuery Module contains functions for handling streamable items.
In contrast to standard XQuery items, a streamable item contains only a reference to the actual data. The data itself will be retrieved if it is requested by an expression, or if the item is to be serialized. Hence, a streamable item only uses a few bytes, and no additional memory is occupied during serialization.
The following BaseX functions return streamable items:
- Streamable Base64 binaries:
- Streamable strings:
Some functions are capable of consuming items in a streamable fashion: data will never be cached, but instead passed on to another target (file, the calling expression, etc.). The following streaming functions are currently available:
The XQuery expression serves as an example on how large files can be downloaded and written to a file with constant memory consumption:
file:write-binary('output.data', fetch:binary('http://files.basex.org/xml/xmark111mb.zip'))
Conventions
All functions in this module are assigned to the http://basex.org/modules/stream namespace, which is statically bound to the stream prefix.
All errors are assigned to the http://basex.org/errors namespace, which is statically bound to the bxerr prefix.
Functions
stream:materialize
| Signatures | stream:materialize($item as item()) as item()
|
| Summary | Returns a materialized instance of the specified $item:
Materialization is helpful if a value is to be processed more than once. It is even mandatory if a value will be invalidated before it is processed (see the example below). |
| Example | In the following example, a file will be deleted before its content is returned. To avoid a "file not found" error, the content will first be materialized:
let $file := 'data.txt' let $data := stream:materialize(file:read-text($file)) return (file:delete($file), $data) |
stream:is-streamable
| Signatures | stream:is-streamable($item as item()) as item()
|
| Summary | Checks if the specified $item is streamable.
|
Changelog
This module was introduced with Version 7.7.
