154 lines
4.3 KiB
ReStructuredText
154 lines
4.3 KiB
ReStructuredText
Calculation with a jinja type
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===============================
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.. objectives:: Objectives
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In this section we will learn how to create new ways of calculation.
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Up to now, our only way of dynamically (that is, during the runtime) calculating
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a value is to point on another variable's value. But this is not the only way.
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A jinja calculated variable's hidden property
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------------------------------------------------
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We can hide or disable some variables or families with other techniques than
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pointing on a variable's value.
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Let's reason on the previous HTTPS proxy configuration's manual mode:
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.. code-block:: yaml
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manual:
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use_for_https:
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description: Also use this proxy for HTTPS
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default: true
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https_proxy:
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type: family
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description: HTTPS Proxy
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hidden:
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variable: manual.use_for_https
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This is extracted from the proxy's manual configuration we discussed before.
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We see here that there is an `https_proxy` family that is going to be hidden
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depending on the value of another variable:
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.. code-block:: yaml
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https_proxy:
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type: family
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hidden:
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variable: manual.use_for_https
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Now we could write it like that:
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.. code-block:: yaml
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manual:
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use_for_https:
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description: Also use this proxy for HTTPS
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default: true
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https_proxy:
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description: HTTPS Proxy
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type: family
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hidden:
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type: jinja
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jinja: |
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{% if rougail.manual.use_for_https %}
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the HTTPS Proxy family is hidden
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{% endif %}
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Yes, it's done in a more complicated (but more powerful) way.
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Let's explain this a little:
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We have replaced this simple hidden property declaration:
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.. code-block:: yaml
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hidden:
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variable: manual.use_for_https
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by this (more complicated) hidden property declaration:
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.. code-block:: yaml
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hidden:
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type: jinja
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jinja: |
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{% if rougail.manual.use_for_https %}
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the HTTPS Proxy family is hidden
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{% endif %}
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The fact is that it has same result, but here we have more possibilities.
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The hidden process is done by a calculation.
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Another jinja calculation type sample
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---------------------------------------
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We can now hide or disable some variables or families with other techniques than
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pointing on a variable's value.
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Let's reason upon the proxy's manual configuration we discussed before.
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We have the :file:`dict/02-proxy_manual.yml` structure file:
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.. code-block:: yaml
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:caption: the :file:`structfile/02-proxy_manual.yml` file
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---
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version: '1.1'
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manual:
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description: Manual proxy configuration
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type: family
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disabled:
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type: jinja
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jinja: |
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{% if rougail.proxy.proxy_mode != 'Manual proxy configuration' %}
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the proxy mode is not manual
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{% endif %}
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.. questions:: Question
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**question**: OK then. What happens when you select the "Manual proxy configuration"?
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Here if the user selects the "Manual proxy configuration" proxy mode,
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the the `manual` family will be disabled. This is what the jinja code says.
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Let's explain it more precisely.
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.. note:: The "the proxy mode is not manual" output is be used in the log outputs
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for example while
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Why Jinja?
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---------------
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.. questions:: What about this `Jinja` type?
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If the :term:`Jinja` template returns some text, then the family will be `disabled`. Otherwise it is accessible.
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Deactivating a family means that we will not be able to access it as well as the variables or families included in this family.
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.. note:: If the Jinja template does not return any text, the variable will be **enabled**.
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Here we are using the Jinja condition statement.
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.. glossary::
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Jinja
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`Jinja <https://jinja.palletsprojects.com>`_ is a template engine.
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we are using Jinja in a classical way, that is, Jinja allows us to handle different cases,
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for example with the `if` statement.
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.. todo:: montrer aussi ici des exemples de calculs de valeurs variables, ce qui est un des usages principaux de jinja
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.. keypoints:: Key points
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Here we have come to the possibility of making any kind of calculations based on the state of the :term:`configuration`.
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This is an important feature to manage the stateful aspect of a configuration.
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