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<div class="section" id="indexing-and-searching-document-hierarchies">
<h1>Indexing and searching document hierarchies<a class="headerlink" href="#indexing-and-searching-document-hierarchies" title="Permalink to this headline">¶</a></h1>
<div class="section" id="overview">
<h2>Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
<p>Whoosh’s full-text index is essentially a flat database of documents. However,
Whoosh supports two techniques for simulating the indexing and querying of
hierarchical documents, that is, sets of documents that form a parent-child
hierarchy, such as “Chapter - Section - Paragraph” or
“Module - Class - Method”.</p>
<p>You can specify parent-child relationships <em>at indexing time</em>, by grouping
documents in the same hierarchy, and then use the
<a class="reference internal" href="api/query.html#whoosh.query.NestedParent" title="whoosh.query.NestedParent"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.query.NestedParent</span></tt></a> and/or <a class="reference internal" href="api/query.html#whoosh.query.NestedChildren" title="whoosh.query.NestedChildren"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.query.NestedChildren</span></tt></a>
to find parents based on their children or vice-versa.</p>
<p>Alternatively, you can use <em>query time joins</em>, essentially like external key
joins in a database, where you perform one search to find a relevant document,
then use a stored value on that document (for example, a <tt class="docutils literal"><span class="pre">parent</span></tt> field) to
look up another document.</p>
<p>Both methods have pros and cons.</p>
</div>
<div class="section" id="using-nested-document-indexing">
<h2>Using nested document indexing<a class="headerlink" href="#using-nested-document-indexing" title="Permalink to this headline">¶</a></h2>
<div class="section" id="indexing">
<h3>Indexing<a class="headerlink" href="#indexing" title="Permalink to this headline">¶</a></h3>
<p>This method works by indexing a “parent” document and all its “child” documents
<em>as a “group”</em> so they are guaranteed to end up in the same segment. You can
use the context manager returned by <tt class="docutils literal"><span class="pre">IndexWriter.group()</span></tt> to group
documents:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">ix</span><span class="o">.</span><span class="n">writer</span><span class="p">()</span> <span class="k">as</span> <span class="n">w</span><span class="p">:</span>
<span class="k">with</span> <span class="n">w</span><span class="o">.</span><span class="n">group</span><span class="p">():</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"Index"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add document"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add reader"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"close"</span><span class="p">)</span>
<span class="k">with</span> <span class="n">w</span><span class="o">.</span><span class="n">group</span><span class="p">():</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"Accumulator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"get result"</span><span class="p">)</span>
<span class="k">with</span> <span class="n">w</span><span class="o">.</span><span class="n">group</span><span class="p">():</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add all"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add some"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"multiply"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"close"</span><span class="p">)</span>
<span class="k">with</span> <span class="n">w</span><span class="o">.</span><span class="n">group</span><span class="p">():</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"Deleter"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"delete"</span><span class="p">)</span>
</pre></div>
</div>
<p>Alternatively you can use the <tt class="docutils literal"><span class="pre">start_group()</span></tt> and <tt class="docutils literal"><span class="pre">end_group()</span></tt> methods:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">ix</span><span class="o">.</span><span class="n">writer</span><span class="p">()</span> <span class="k">as</span> <span class="n">w</span><span class="p">:</span>
<span class="n">w</span><span class="o">.</span><span class="n">start_group</span><span class="p">()</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"Index"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add document"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"add reader"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">"close"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">end_group</span><span class="p">()</span>
</pre></div>
</div>
<p>Each level of the hierarchy should have a query that distinguishes it from
other levels (for example, in the above index, you can use <tt class="docutils literal"><span class="pre">kind:class</span></tt> or
<tt class="docutils literal"><span class="pre">kind:method</span></tt> to match different levels of the hierarchy).</p>
<p>Once you’ve indexed the hierarchy of documents, you can use two query types to
find parents based on children or vice-versa.</p>
<p>(There is currently no support in the default query parser for nested queries.)</p>
</div>
<div class="section" id="nestedparent-query">
<h3>NestedParent query<a class="headerlink" href="#nestedparent-query" title="Permalink to this headline">¶</a></h3>
<p>The <a class="reference internal" href="api/query.html#whoosh.query.NestedParent" title="whoosh.query.NestedParent"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.query.NestedParent</span></tt></a> query type lets you specify a query for
child documents, but have the query return an “ancestor” document from higher
in the hierarchy:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># First, we need a query that matches all the documents in the "parent"</span>
<span class="c"># level we want of the hierarchy</span>
<span class="n">all_parents</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"kind"</span><span class="p">,</span> <span class="s">"class"</span><span class="p">)</span>
<span class="c"># Then, we need a query that matches the children we want to find</span>
<span class="n">wanted_kids</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"close"</span><span class="p">)</span>
<span class="c"># Now we can make a query that will match documents where "name" is</span>
<span class="c"># "close", but the query will return the "parent" documents of the matching</span>
<span class="c"># children</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">NestedParent</span><span class="p">(</span><span class="n">all_parents</span><span class="p">,</span> <span class="n">wanted_kids</span><span class="p">)</span>
<span class="c"># results = Index, Calculator</span>
</pre></div>
</div>
<p>Note that in a hierarchy with more than two levels, you can specify a “parents”
query that matches any level of the hierarchy, so you can return the top-level
ancestors of the matching children, or the second level, third level, etc.</p>
<p>The query works by first building a bit vector representing which documents are
“parents”:</p>
<div class="highlight-python"><pre>Index
| Calculator
| |
1000100100000100
| |
| Deleter
Accumulator</pre>
</div>
<p>Then for each match of the “child” query, it calculates the previous parent
from the bit vector and returns it as a match (it only returns each parent once
no matter how many children match). This parent lookup is very efficient:</p>
<div class="highlight-python"><pre>1000100100000100
|
|<-+ close</pre>
</div>
</div>
<div class="section" id="nestedchildren-query">
<h3>NestedChildren query<a class="headerlink" href="#nestedchildren-query" title="Permalink to this headline">¶</a></h3>
<p>The opposite of <tt class="docutils literal"><span class="pre">NestedParent</span></tt> is <a class="reference internal" href="api/query.html#whoosh.query.NestedChildren" title="whoosh.query.NestedChildren"><tt class="xref py py-class docutils literal"><span class="pre">whoosh.query.NestedChildren</span></tt></a>. This
query lets you match parents but return their children. This is useful, for
example, to search for an album title and return the songs in the album:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Query that matches all documents in the "parent" level we want to match</span>
<span class="c"># at</span>
<span class="n">all_parents</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"kind"</span><span class="p">,</span> <span class="s">"album"</span><span class="p">)</span>
<span class="c"># Parent documents we want to match</span>
<span class="n">wanted_parents</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"album_title"</span><span class="p">,</span> <span class="s">"heaven"</span><span class="p">)</span>
<span class="c"># Now we can make a query that will match parent documents where "album_title"</span>
<span class="c"># contains "heaven", but the query will return the "child" documents of the</span>
<span class="c"># matching parents</span>
<span class="n">q1</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">NestedChildren</span><span class="p">(</span><span class="n">all_parents</span><span class="p">,</span> <span class="n">wanted_parents</span><span class="p">)</span>
</pre></div>
</div>
<p>You can then combine that query with an <tt class="docutils literal"><span class="pre">AND</span></tt> clause, for example to find
songs with “hell” in the song title that occur on albums with “heaven” in the
album title:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">q2</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">And</span><span class="p">([</span><span class="n">q1</span><span class="p">,</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"song_title"</span><span class="p">,</span> <span class="s">"hell"</span><span class="p">)])</span>
</pre></div>
</div>
</div>
<div class="section" id="deleting-and-updating-hierarchical-documents">
<h3>Deleting and updating hierarchical documents<a class="headerlink" href="#deleting-and-updating-hierarchical-documents" title="Permalink to this headline">¶</a></h3>
<p>The drawback of the index-time method is <em>updating and deleting</em>. Because the
implementation of the queries depends on the parent and child documents being
contiguous in the segment, you can’t update/delete just one child document.
You can only update/delete an entire top-level document at once (for example,
if your hierarchy is “Chapter - Section - Paragraph”, you can only update or
delete entire chapters, not a section or paragraph). If the top-level of the
hierarchy represents very large blocks of text, this can involve a lot of
deleting and reindexing.</p>
<p>Currently <tt class="docutils literal"><span class="pre">Writer.update_document()</span></tt> does not automatically work with nested
documents. You must manually delete and re-add document groups to update them.</p>
<p>To delete nested document groups, use the <tt class="docutils literal"><span class="pre">Writer.delete_by_query()</span></tt>
method with a <tt class="docutils literal"><span class="pre">NestedParent</span></tt> query:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Delete the "Accumulator" class</span>
<span class="n">all_parents</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"kind"</span><span class="p">,</span> <span class="s">"class"</span><span class="p">)</span>
<span class="n">to_delete</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"Accumulator"</span><span class="p">)</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">NestedParent</span><span class="p">(</span><span class="n">all_parents</span><span class="p">,</span> <span class="n">to_delete</span><span class="p">)</span>
<span class="k">with</span> <span class="n">myindex</span><span class="o">.</span><span class="n">writer</span><span class="p">()</span> <span class="k">as</span> <span class="n">w</span><span class="p">:</span>
<span class="n">w</span><span class="o">.</span><span class="n">delete_by_query</span><span class="p">(</span><span class="n">q</span><span class="p">)</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="using-query-time-joins">
<h2>Using query-time joins<a class="headerlink" href="#using-query-time-joins" title="Permalink to this headline">¶</a></h2>
<p>A second technique for simulating hierarchical documents in Whoosh involves
using a stored field on each document to point to its parent, and then using
the value of that field at query time to find parents and children.</p>
<p>For example, if we index a hierarchy of classes and methods using pointers
to parents instead of nesting:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Store a pointer to the parent on each "method" document</span>
<span class="k">with</span> <span class="n">ix</span><span class="o">.</span><span class="n">writer</span><span class="p">()</span> <span class="k">as</span> <span class="n">w</span><span class="p">:</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">c_name</span><span class="o">=</span><span class="s">"Index"</span><span class="p">,</span> <span class="n">docstring</span><span class="o">=</span><span class="s">"..."</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add document"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Index"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add reader"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Index"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"close"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Index"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">c_name</span><span class="o">=</span><span class="s">"Accumulator"</span><span class="p">,</span> <span class="n">docstring</span><span class="o">=</span><span class="s">"..."</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Accumulator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"get result"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Accumulator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">c_name</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">,</span> <span class="n">docstring</span><span class="o">=</span><span class="s">"..."</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add all"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add some"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"multiply"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"close"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Calculator"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"class"</span><span class="p">,</span> <span class="n">c_name</span><span class="o">=</span><span class="s">"Deleter"</span><span class="p">,</span> <span class="n">docstring</span><span class="o">=</span><span class="s">"..."</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"add"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Deleter"</span><span class="p">)</span>
<span class="n">w</span><span class="o">.</span><span class="n">add_document</span><span class="p">(</span><span class="n">kind</span><span class="o">=</span><span class="s">"method"</span><span class="p">,</span> <span class="n">m_name</span><span class="o">=</span><span class="s">"delete"</span><span class="p">,</span> <span class="n">parent</span><span class="o">=</span><span class="s">"Deleter"</span><span class="p">)</span>
<span class="c"># Now do manual joins at query time</span>
<span class="k">with</span> <span class="n">ix</span><span class="o">.</span><span class="n">searcher</span><span class="p">()</span> <span class="k">as</span> <span class="n">s</span><span class="p">:</span>
<span class="c"># Tip: Searcher.document() and Searcher.documents() let you look up</span>
<span class="c"># documents by field values more easily than using Searcher.search()</span>
<span class="c"># Children to parents:</span>
<span class="c"># Print the docstrings of classes on which "close" methods occur</span>
<span class="k">for</span> <span class="n">child_doc</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">documents</span><span class="p">(</span><span class="n">m_name</span><span class="o">=</span><span class="s">"close"</span><span class="p">):</span>
<span class="c"># Use the stored value of the "parent" field to look up the parent</span>
<span class="c"># document</span>
<span class="n">parent_doc</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">document</span><span class="p">(</span><span class="n">c_name</span><span class="o">=</span><span class="n">child_doc</span><span class="p">[</span><span class="s">"parent"</span><span class="p">])</span>
<span class="c"># Print the parent document's stored docstring field</span>
<span class="k">print</span><span class="p">(</span><span class="n">parent_doc</span><span class="p">[</span><span class="s">"docstring"</span><span class="p">])</span>
<span class="c"># Parents to children:</span>
<span class="c"># Find classes with "big" in the docstring and print their methods</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"kind"</span><span class="p">,</span> <span class="s">"class"</span><span class="p">)</span> <span class="o">&</span> <span class="n">query</span><span class="o">.</span><span class="n">Term</span><span class="p">(</span><span class="s">"docstring"</span><span class="p">,</span> <span class="s">"big"</span><span class="p">)</span>
<span class="k">for</span> <span class="n">hit</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">q</span><span class="p">,</span> <span class="n">limit</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="s">"Class name="</span><span class="p">,</span> <span class="n">hit</span><span class="p">[</span><span class="s">"c_name"</span><span class="p">],</span> <span class="s">"methods:"</span><span class="p">)</span>
<span class="k">for</span> <span class="n">child_doc</span> <span class="ow">in</span> <span class="n">s</span><span class="o">.</span><span class="n">documents</span><span class="p">(</span><span class="n">parent</span><span class="o">=</span><span class="n">hit</span><span class="p">[</span><span class="s">"c_name"</span><span class="p">]):</span>
<span class="k">print</span><span class="p">(</span><span class="s">" Method name="</span><span class="p">,</span> <span class="n">child_doc</span><span class="p">[</span><span class="s">"m_name"</span><span class="p">])</span>
</pre></div>
</div>
<p>This technique is more flexible than index-time nesting in that you can
delete/update individual documents in the hierarchy piece by piece, although it
doesn’t support finding different parent levels as easily. It is also slower
than index-time nesting (potentially much slower), since you must perform
additional searches for each found document.</p>
<p>Future versions of Whoosh may include “join” queries to make this process more
efficient (or at least more automatic).</p>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Indexing and searching document hierarchies</a><ul>
<li><a class="reference internal" href="#overview">Overview</a></li>
<li><a class="reference internal" href="#using-nested-document-indexing">Using nested document indexing</a><ul>
<li><a class="reference internal" href="#indexing">Indexing</a></li>
<li><a class="reference internal" href="#nestedparent-query">NestedParent query</a></li>
<li><a class="reference internal" href="#nestedchildren-query">NestedChildren query</a></li>
<li><a class="reference internal" href="#deleting-and-updating-hierarchical-documents">Deleting and updating hierarchical documents</a></li>
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<li><a class="reference internal" href="#using-query-time-joins">Using query-time joins</a></li>
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