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<div class="section" id="how-to-implement-a-new-backend">
<h1>How to implement a new backend<a class="headerlink" href="#how-to-implement-a-new-backend" title="Permalink to this headline">¶</a></h1>
<div class="section" id="index">
<h2>Index<a class="headerlink" href="#index" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>Subclass <a class="reference internal" href="../api/index.html#whoosh.index.Index" title="whoosh.index.Index"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.index.Index</span></tt></a>.</li>
<li>Indexes must implement the following methods.<ul>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.is_empty" title="whoosh.index.Index.is_empty"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.is_empty()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.doc_count" title="whoosh.index.Index.doc_count"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.doc_count()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.reader" title="whoosh.index.Index.reader"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.reader()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.writer" title="whoosh.index.Index.writer"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.writer()</span></tt></a></li>
</ul>
</li>
<li>Indexes that require/support locking must implement the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.lock()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.unlock()</span></tt></li>
</ul>
</li>
<li>Indexes that support deletion must implement the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.delete_document()</span></tt></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.doc_count_all" title="whoosh.index.Index.doc_count_all"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.doc_count_all()</span></tt></a> – if the backend has delayed
deletion.</li>
</ul>
</li>
<li>Indexes that require/support versioning/transactions <em>may</em> implement the following methods.<ul>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.latest_generation" title="whoosh.index.Index.latest_generation"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.latest_generation()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.up_to_date" title="whoosh.index.Index.up_to_date"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.up_to_date()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.last_modified" title="whoosh.index.Index.last_modified"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.last_modified()</span></tt></a></li>
</ul>
</li>
<li>Index <em>may</em> implement the following methods (the base class’s versions are no-ops).<ul>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.optimize" title="whoosh.index.Index.optimize"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.optimize()</span></tt></a></li>
<li><a class="reference internal" href="../api/index.html#whoosh.index.Index.close" title="whoosh.index.Index.close"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.index.Index.close()</span></tt></a></li>
</ul>
</li>
</ul>
</div>
<div class="section" id="indexwriter">
<h2>IndexWriter<a class="headerlink" href="#indexwriter" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>Subclass <a class="reference internal" href="../api/writing.html#whoosh.writing.IndexWriter" title="whoosh.writing.IndexWriter"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.writing.IndexWriter</span></tt></a>.</li>
<li>IndexWriters must implement the following methods.<ul>
<li><a class="reference internal" href="../api/writing.html#whoosh.writing.IndexWriter.add_document" title="whoosh.writing.IndexWriter.add_document"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.writing.IndexWriter.add_document()</span></tt></a></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.writing.IndexWriter.add_reader()</span></tt></li>
</ul>
</li>
<li>Backends that support deletion must implement the following methods.<ul>
<li><a class="reference internal" href="../api/writing.html#whoosh.writing.IndexWriter.delete_document" title="whoosh.writing.IndexWriter.delete_document"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.writing.IndexWriter.delete_document()</span></tt></a></li>
</ul>
</li>
<li>IndexWriters that work as transactions must implement the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexWriter.commit()</span></tt> – Save the additions/deletions done with
this IndexWriter to the main index, and release any resources used by the IndexWriter.</li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexWriter.cancel()</span></tt> – Throw away any additions/deletions done
with this IndexWriter, and release any resources used by the IndexWriter.</li>
</ul>
</li>
</ul>
</div>
<div class="section" id="indexreader">
<h2>IndexReader<a class="headerlink" href="#indexreader" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>Subclass <a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader" title="whoosh.reading.IndexReader"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.reading.IndexReader</span></tt></a>.</li>
<li>IndexReaders must implement the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.__contains__()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.__iter__()</span></tt></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.iter_from" title="whoosh.reading.IndexReader.iter_from"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.iter_from()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.stored_fields" title="whoosh.reading.IndexReader.stored_fields"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.stored_fields()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.doc_count_all" title="whoosh.reading.IndexReader.doc_count_all"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.doc_count_all()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.doc_count" title="whoosh.reading.IndexReader.doc_count"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.doc_count()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.doc_field_length" title="whoosh.reading.IndexReader.doc_field_length"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.doc_field_length()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.field_length" title="whoosh.reading.IndexReader.field_length"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.field_length()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.max_field_length" title="whoosh.reading.IndexReader.max_field_length"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.max_field_length()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.postings" title="whoosh.reading.IndexReader.postings"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.postings()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.has_vector" title="whoosh.reading.IndexReader.has_vector"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.has_vector()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.vector" title="whoosh.reading.IndexReader.vector"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.vector()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.doc_frequency" title="whoosh.reading.IndexReader.doc_frequency"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.doc_frequency()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.frequency" title="whoosh.reading.IndexReader.frequency"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.frequency()</span></tt></a></li>
</ul>
</li>
<li>Backends that support deleting documents should implement the following
methods.<ul>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.has_deletions" title="whoosh.reading.IndexReader.has_deletions"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.has_deletions()</span></tt></a></li>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.is_deleted" title="whoosh.reading.IndexReader.is_deleted"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.is_deleted()</span></tt></a></li>
</ul>
</li>
<li>Backends that support versioning should implement the following methods.<ul>
<li><a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.generation" title="whoosh.reading.IndexReader.generation"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.generation()</span></tt></a></li>
</ul>
</li>
<li>If the IndexReader object does not keep the schema in the <tt class="docutils literal"><span class="pre">self.schema</span></tt>
attribute, it needs to override the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.field()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.field_names()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.scorable_names()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.vector_names()</span></tt></li>
</ul>
</li>
<li>IndexReaders <em>may</em> implement the following methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.DocReader.close()</span></tt> – closes any open resources associated with the
reader.</li>
</ul>
</li>
</ul>
</div>
<div class="section" id="matcher">
<h2>Matcher<a class="headerlink" href="#matcher" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="../api/reading.html#whoosh.reading.IndexReader.postings" title="whoosh.reading.IndexReader.postings"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.reading.IndexReader.postings()</span></tt></a> method returns a
<a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher" title="whoosh.matching.Matcher"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.matching.Matcher</span></tt></a> object. You will probably need to implement
a custom Matcher class for reading from your posting lists.</p>
<ul class="simple">
<li>Subclass <a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher" title="whoosh.matching.Matcher"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.matching.Matcher</span></tt></a>.</li>
<li>Implement the following methods at minimum.<ul>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.is_active" title="whoosh.matching.Matcher.is_active"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.is_active()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.copy" title="whoosh.matching.Matcher.copy"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.copy()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.id" title="whoosh.matching.Matcher.id"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.id()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.next" title="whoosh.matching.Matcher.next"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.next()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.value" title="whoosh.matching.Matcher.value"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.value()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.value_as" title="whoosh.matching.Matcher.value_as"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.value_as()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.score" title="whoosh.matching.Matcher.score"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.score()</span></tt></a></li>
</ul>
</li>
<li>Depending on the implementation, you <em>may</em> implement the following methods
more efficiently.<ul>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.skip_to" title="whoosh.matching.Matcher.skip_to"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.skip_to()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.weight" title="whoosh.matching.Matcher.weight"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.weight()</span></tt></a></li>
</ul>
</li>
<li>If the implementation supports quality, you should implement the following
methods.<ul>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.supports_quality()</span></tt></li>
<li><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.quality()</span></tt></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.block_quality" title="whoosh.matching.Matcher.block_quality"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.block_quality()</span></tt></a></li>
<li><a class="reference internal" href="../api/matching.html#whoosh.matching.Matcher.skip_to_quality" title="whoosh.matching.Matcher.skip_to_quality"><tt class="xref py py-meth docutils literal"><span class="pre">whoosh.matching.Matcher.skip_to_quality()</span></tt></a></li>
</ul>
</li>
</ul>
</div>
</div>
</div>
</div>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">How to implement a new backend</a><ul>
<li><a class="reference internal" href="#index">Index</a></li>
<li><a class="reference internal" href="#indexwriter">IndexWriter</a></li>
<li><a class="reference internal" href="#indexreader">IndexReader</a></li>
<li><a class="reference internal" href="#matcher">Matcher</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="index.html"
title="previous chapter">Technical notes</a></p>
<h4>Next topic</h4>
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