Lazy Module

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This XQuery Module contains functions for handling streamable items.

In contrast to standard XQuery items, streamable items may take up much less space, because they only contain a reference to the actual data. The data itself will only be retrieved if it is required by another expression, or if an item is serialized. Serialization of streamable items takes constant space.

The following BaseX functions return streamable items:

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.
If an item is streamable, its content will be retrieved, and a new item containing its data will be returned. Other, non-streamable items will simply be passed through.

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.