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.. This work is licensed under a Creative Commons Attribution 4.0 International License.
.. http://creativecommons.org/licenses/by/4.0
.. Copyright (C) 2021 Nordix Foundation
.. DO NOT CHANGE THIS LABEL FOR RELEASE NOTES - EVEN THOUGH IT GIVES A WARNING
.. _design:
CPS Path
########
.. toctree::
:maxdepth: 1
Introduction
============
Several CPS APIs use the CPS path (or cpsPath in Java API) parameter.
The CPS path parameter is used for querying xpaths. CPS path is inspired by the `XML Path Language (XPath) 3.1. <https://www.w3.org/TR/2017/REC-xpath-31-20170321/>`_
This section describes the functionality currently supported by CPS Path.
Sample Data
===========
The xml below describes some basic data to be used to illustrate the CPS Path functionality.
.. code-block:: xml
<shops>
<bookstore name="Chapters">
<bookstore-name>Chapters</bookstore-name>
<categories code="1" name="SciFi" numberOfBooks="2">
<books>
<book title="2001: A Space Odyssey" price="5">
<label>sale</label>
<label>classic</label>
<edition>1968</edition>
<edition>2018</edition>
</book>
<book title="Dune" price="5">
<label>classic</label>
<edition>1965</edition>
</book>
</books>
</categories>
<categories code="2" name="Kids" numberOfBooks="1">
<books>
<book title="Matilda" />
</books>
</categories>
</bookstore>
</shops>
**Note.** 'categories' is a Yang List and 'code' is its key leaf. All other data nodes are Yang Containers. 'label' and 'edition' are both leaf-lists.
General Notes
=============
- String values must be wrapped in quotation marks ``"`` (U+0022) or apostrophes ``'`` (U+0027).
- String comparisons are case sensitive.
- List key-fields containing ``\`` or ``@[`` will not be processed correctly when being referenced with such key values in absolute or descendant paths. This means such entries will be omitted from any query result. See `CPS-500 <https://jira.onap.org/browse/CPS-500>`_ Special Character Limitations of cpsPath Queries
Query Syntax
============
``( <absolute-path> | <descendant-path> ) [ <leaf-conditions> ] [ <text()-condition> ] [ <ancestor-axis> ]``
Each CPS path expression need to start with an 'absolute' or 'descendant' xpath.
absolute-path
-------------
**Syntax**: ``'/' <container-name> ( '[' <list-key> ']' )? ( '/' <containerName> ( '[' <list-key> ']' )? )*``
- ``container name``: Any yang container or list.
- ``list-key``: One or more key-value pairs, each preceded by the ``@`` symbol, combined using the ``and`` keyword.
- The above van repeated any number of times.
**Examples**
- ``/shops/bookstore``
- ``/shops/bookstore/categories[@code=1]``
- ``/shops/bookstore/categories[@code=1]/book``
**Limitations**
- Absolute paths must start with the top element (data node) as per the model tree.
- Each list reference must include a valid instance reference to the key for that list. Except when it is the last element.
descendant-path
---------------
**Syntax**: ``'//' <container-name> ( '[' <list-key> ']' )? ( '/' <containerName> ( '[' <list-key> ']' )? )*``
- The syntax of a descendant path is identical to a absolute path except that it is preceded by a double slash ``//``.
**Examples**
- ``//bookstore``
- ``//categories[@code=1]/book``
- ``//bookstore/categories``
**Limitations**
- Each list reference must include a valid instance reference to the key for that list. Except when it is the last element.
leaf-conditions
---------------
**Syntax**: ``<xpath> '[' @<leaf-name1> '=' <leaf-value1> ( ' and ' @<leaf-name> '=' <leaf-value> )* ']'``
- ``xpath``: Absolute or descendant or xpath to the (list) node which elements will be queried.
- ``leaf-name``: The name of the leaf which value needs to be compared.
- ``leaf-value``: The required value of the leaf.
**Examples**
- ``/shops/bookstore/categories[@numberOfBooks=1]``
- ``//categories[@name="Kids"]``
- ``//categories[@name='Kids']``
- ``//categories[@code=1]/books/book[@title='Dune' and @price=5]``
**Limitations**
- Only the last list or container can be queried leaf values. Any ancestor list will have to be referenced by its key name-value pair(s).
- Multiple attributes can only be combined using ``and``. ``or`` and bracketing is not supported.
- Only leaves can be used, leaf-list are not supported.
- Only string and integer values are supported, boolean and float values are not supported.
**Notes**
- For performance reasons it does not make sense to query using key leaf as attribute. If the key value is known it is better to execute a get request with the complete xpath.
text()-condition
----------------
The text()-condition can be added to any CPS path query.
**Syntax**: ``<cps-path> ( '/' <leaf-name> '[text()=' <string-value> ']' )?``
- ``cps-path``: Any CPS path query.
- ``leaf-name``: The name of the leaf or leaf-list which value needs to be compared.
- ``string-value``: The required value of the leaf or leaf-list element as a string wrapped in quotation marks (U+0022) or apostrophes (U+0027). This wil still match integer values.
**Examples**
- ``//book/label[text()="classic"]``
- ``//book/edition[text()="1965"]``
**Limitations**
- Only the last list or container can be queried for leaf values with a text() condition. Any ancestor list will have to be referenced by its key name-value pair(s).
- Only one leaf or leaf-list can be tested.
- Only string and integer values are supported, boolean and float values are not supported.
- Since CPS cannot return individual leaves it will always return the container with all its leaves. Ancestor-axis can be used to specify a parent higher up the tree.
- When querying a leaf value (instead of leaf-list) it is better, more performant to use a text value condition use @<leaf-name> as described above.
ancestor-axis
-------------
The ancestor axis can be added to any CPS path query but has to be the last part.
**Syntax**: ``<cps-path> ( '/ancestor::' <ancestor-path> )?``
- ``cps-path``: Any CPS path query.
- ``ancestor-path``: Partial path to ancestors of the target node. This can contain one or more ancestor nodes separated by a ``/``.
**Examples**
- ``//book/ancestor::categories``
- ``//categories[@genre="SciFi"]/book/ancestor::bookstore``
- ``book/ancestor::categories[@code=1]/books``
- ``//book/label[text()="classic"]/ancestor::shop``
**Limitations**
- Ancestor list elements can only be addressed using the list key leaf.
- List elements with compound keys are not supported.
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