295 lines
14 KiB
HTML
295 lines
14 KiB
HTML
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<!-- Place this tag in your head or just before your close body tag. -->
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<div class="plugin">
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<div class="col-sm-12">
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<h1>Plugin – lektor-limit-dependencies 1.0.0</h1>
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</div>
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</div>
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<div class="row">
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<div class="col-sm-1"></div>
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<div class="col-sm-11">
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<p>Lektor plugin to limit dependencies created by queries<p>
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</div>
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</div>
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<div class="row">
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<div class="col-sm-3 plugin-margin">
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<h4>Project links</h4>
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<ul class="tree-nav">
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<li><a href="https://pypi.org/project/lektor-limit-dependencies/" class="ext">Homepage</a></li>
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</ul>
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<div class="separator">
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<h4>Meta</h4>
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</div>
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<p><strong>Version:</strong> 1.0.0</p>
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<p><strong>Author:</strong>
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<a href="mailto:dairiki@dairiki.org">Jeff Dairiki</a>
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</p>
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<div class="separator">
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<h4>Tags</h4>
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</div>
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<a href="../tag/build-optimization/">build optimization</a>,
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<a href="../tag/Jinja-filters/">Jinja filters</a>,
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and
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<a href="../tag/setup-env/">setup-env</a>
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<p>
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View <a href="../tags/" class="ref">all tags</a>.
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</p>
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</div>
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<div class="col-sm-9 doc-styling">
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<h2>Project Description</h2>
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<h1>Lektor Limit Dependencies</h1>
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<p><a href="https://pypi.org/project/lektor-limit-dependencies/" rel="nofollow"><img src="https://img.shields.io/pypi/v/lektor-limit-dependencies.svg" alt="PyPI version"></a>
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<a href="https://pypi.python.org/pypi/lektor-limit-dependencies/" rel="nofollow"><img src="https://img.shields.io/pypi/pyversions/lektor-limit-dependencies.svg" alt="PyPI Supported Python Versions"></a>
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<a href="https://github.com/dairiki/lektor-limit-dependencies/blob/master/LICENSE" rel="nofollow"><img src="https://img.shields.io/github/license/dairiki/lektor-limit-dependencies" alt="GitHub license"></a>
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<a href="https://github.com/dairiki/lektor-limit-dependencies" rel="nofollow"><img src="https://github.com/dairiki/lektor-limit-dependencies/workflows/Tests/badge.svg" alt="GitHub Actions (Tests)"></a></p>
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<p>This is an experimental <a href="https://www.getlektor.com/" rel="nofollow">Lektor</a> plugin which aims to provide tools (or,
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at least, a tool) to help keep Lektor’s dependency tracking under
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control.</p>
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<h2>Introduction</h2>
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<h3>Motivating Example</h3>
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<p>Suppose that you would like to list the three most recent blog posts
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in the sidebar of your Lektor-based site. This can be done by adding
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something like to your site base template:</p>
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<pre lang="html+jinja"><span class="p"><</span><span class="nt">h3</span><span class="p">></span>Recent Posts<span class="p"></</span><span class="nt">h3</span><span class="p">></span>
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<span class="p"><</span><span class="nt">ul</span><span class="p">></span>
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<span class="cp">{%</span> <span class="k">for</span> <span class="nv">post</span> <span class="k">in</span> <span class="nv">site.query</span><span class="o">(</span><span class="s1">'/blog'</span><span class="o">)</span><span class="nv">.order_by</span><span class="o">(</span><span class="s1">'-pub_date'</span><span class="o">)</span><span class="nv">.limit</span><span class="o">(</span><span class="m">3</span><span class="o">)</span> <span class="cp">%}</span>
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<span class="p"><</span><span class="nt">li</span><span class="p">><</span><span class="nt">a</span> <span class="na">href</span><span class="o">=</span><span class="s">"</span><span class="cp">{{</span> <span class="nv">post</span><span class="o">|</span><span class="nf">url</span> <span class="cp">}}</span><span class="s">"</span><span class="p">></span><span class="cp">{{</span> <span class="nv">post.title</span> <span class="cp">}}</span><span class="p"></</span><span class="nt">a</span><span class="p">></</span><span class="nt">li</span><span class="p">></span>
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<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
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<span class="p"></</span><span class="nt">ul</span><span class="p">></span>
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</pre>
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<p>This is not without drawbacks, however. To sort the post query by
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date, Lektor iterates through <em><strong>all</strong></em> of the blog’s posts, then sorts
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them. In so doing, it records all of the blog posts as dependencies
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<em>of every page on which this most-recent-post query is used</em>. If this
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is in the sidebar of every page on your site, <em>now every page on your
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site will be rebuilt whenever any blog post at all</em> (not just one of
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the three most recent posts) <em>is edited</em>.</p>
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<p>Technically, it is true that all pages now depend on all posts. You
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might well edit the <code>pub_date</code> of one of your older posts, such that
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it should now appear in the most-recent listing. However, it is not
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true that all pages need to be rebuilt for <em>any</em> edit of any post.
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Unfortunately, Lektor’s dependency tracking system is not elaborate
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enough to be able to express details about <em>how</em> pages are
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dependent on other pages; it only records that they <em>are</em>
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dependent, so Lektor has no option but to rebuild everything.</p>
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<h3>A Solution?</h3>
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<p>This plugin introduces a Jinja filter, <code>limit_dependencies</code>. It
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expects, as input, a Lektor <a href="https://www.getlektor.com/docs/api/db/query/" title="Lektor documentation on the Query class" rel="nofollow">query</a> instance. It iterates through the
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input query, and returns a new query instance which will yield the
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same results. While it is doing its iteration, it — essentially —
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monkey-patches Lektor’s dependency tracking machinery to prevent it
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from recording any dependencies.</p>
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<p>At the end, <code>limit_dependencies</code> records one dependency on a <a href="https://www.getlektor.com/docs/api/db/obj/#virtual-source-objects" title="Lektor documentation on Virtual Source Objects" rel="nofollow">virtual
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source object</a> which depends only on the sequence of the identities
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of the records in the query result. (Lektor provides a means by which
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virtual source objects can report checksums. The
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dependency tracking mechanism records those checksums, and will
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trigger a rebuild should the checksum change. <code>Limit_dependencies</code>
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generates a virtual source object whose checksum depends on the
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sequence of identities in the query result.)</p>
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<p>In the above example, this is exactly what we want. We only want to
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trigger a rebuild if the order or composition of the most-recent three
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posts changes. (Or if any of their titles change. Note that this
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gets covered, too, since when the resulting query is iterated over in
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the <code>{% for %}</code> loop, dependencies will be recorded on the three
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most-recent posts.)</p>
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<p>Thus, the example above, if replaced by:</p>
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<pre lang="html+jinja"><span class="p"><</span><span class="nt">h3</span><span class="p">></span>Recent Posts<span class="p"></</span><span class="nt">h3</span><span class="p">></span>
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<span class="p"><</span><span class="nt">ul</span><span class="p">></span>
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<span class="cp">{%</span> <span class="k">for</span> <span class="nv">post</span> <span class="k">in</span> <span class="nv">site.query</span><span class="o">(</span><span class="s1">'/blog'</span><span class="o">)</span><span class="nv">.order_by</span><span class="o">(</span><span class="s1">'-pub_date'</span><span class="o">)</span><span class="nv">.limit</span><span class="o">(</span><span class="m">3</span><span class="o">)|</span><span class="nf">limit_dependencies</span> <span class="cp">%}</span>
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<span class="p"><</span><span class="nt">li</span><span class="p">><</span><span class="nt">a</span> <span class="na">href</span><span class="o">=</span><span class="s">"</span><span class="cp">{{</span> <span class="nv">post</span><span class="o">|</span><span class="nf">url</span> <span class="cp">}}</span><span class="s">"</span><span class="p">></span><span class="cp">{{</span> <span class="nv">post.title</span> <span class="cp">}}</span><span class="p"></</span><span class="nt">a</span><span class="p">></</span><span class="nt">li</span><span class="p">></span>
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<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
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<span class="p"></</span><span class="nt">ul</span><span class="p">></span>
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</pre>
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<p>will work in a much more efficient and sane manner. Pages will be
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rebuilt only if there are changes in the order, composition or content
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of the three most recent posts.</p>
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<h2>Installation</h2>
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<p>Add lektor-limit-dependencies to your project from command line:</p>
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<pre><code>lektor plugins add lektor-limit-dependencies
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</code></pre>
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<p>See <a href="https://www.getlektor.com/docs/plugins/" rel="nofollow">the Lektor plugin documentation</a> for more information.</p>
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<h2>Author</h2>
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<p>Jeff Dairiki <a href="mailto:dairiki@dairiki.org" rel="nofollow">dairiki@dairiki.org</a></p>
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<h2>Changelog</h2>
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<h3>Release 1.0.0 (2023-01-31)</h3>
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<p>No code changes from 1.0.0b1.</p>
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<p>Test under python 3.11.</p>
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<h3>Release 1.0.0b1 (2021-03-29)</h3>
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<p>Drop support for python<3.7 and lektor<3.3.</p>
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<h3>Release 0.1 (2021-02-05)</h3>
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<p>No code changes.</p>
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<p>Update development status classifier to "stable".</p>
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<p>Test under python 3.9. Stop testing under 3.5.</p>
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<h3>Release 0.1a1 (2020-05-19)</h3>
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<p>Initial release.</p>
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