title: Combining hits from multiple documents into a single hit in Lucene
body: <p>I am trying to get a particular search to work and it is proving problematic. The actual source data is quite complex but can be summarised by the following example:</p>
  
  <blockquote>
    <p>I have articles that are indexed so
    that they can be searched. Each
    article also has multiple properties
    associated with it which are also
    indexed and searchable. When users
    search, they can get hits in either
    the main article or the associated
    properties. Regardless of where a hit
    is achieved, the article is returned
    as a search hit (ie. the properties
    are never a hit in their own right).</p>
  </blockquote>
  
  <p>Now for the complexity:</p>
  
  <blockquote>
    <p>Each property has security on it,
    which means that for any given user,
    they may or may not be able to see the
    property. If a user cannot see a
    property, they obviously do not get a
    search hit in it. This security check
    is proprietary and cannot be done
    using the typical mechanism of storing
    a role in the index alongside the
    other fields in the document.</p>
  </blockquote>
  
  <p>I currently have an index that contains the articles and properties indexed separately (ie. an article is indexed as a document, and each property has its own document). When a search happens, a hit in article A or a hit in any of the properties of article A should be classed as hit for article A alone, with the scores combined.</p>
  
  <p>To achieve this originally, Lucene v1.3 was modified to allow this to happen by changing BooleanQuery to have a custom Scorer that could apply the logic of the security check and the combination of two hits in different documents being classed as a hit in a single document. I am trying to upgrade this version to the latest (v2.3.2 - I am using Lucene.Net), but ideally without having to modify Lucene in any way.</p>
  
  <p>An additional problem occurs if I do an AND search. If an article contains the word <em>foo</em> and one of its properties contains the word <em>bar</em>, then searching for "foo AND bar" will return the article as a hit. My current code deals with this inside the custom Scorer.</p>
  
  <p>Any ideas how/if this can be done?</p>
  
  <p><em>I am thinking along the lines of using a custom HitCollector and passing that into the search, but when doing the boolean search "foo AND bar", execution never reaches my HitCollector as the ConjunctionScorer filters out all of the results from the sub-queries before getting there.</em></p>
  
  <hr>
  
  <p><strong>EDIT:</strong> </p>
  
  <p>Whether or not a user can see a property is not based on the property itself, but on the value of the property. I cannot therefore put the extra security conditions into the query upfront as I don't know the value to filter by.</p>
  
  <p>As an example:</p>
  
  <pre><code>+---------+------------+------------+
  | Article | Property 1 | Property 2 |
  +---------+------------+------------+
  |    A    |     X      |     J      |
  |    B    |     Y      |     K      |
  |    C    |     Z      |     L      |
  +---------+------------+------------+
  </code></pre>
  
  <p>If a user can see everything, then searching for "B and Y" will return a single search result for article B.</p>
  
  <p>If another user cannot see a property if its value contains Y, then searching for "B and Y" will return no hits.</p>
  
  <p>I have no way of knowing what values a user can and cannot see upfront. They only way to tell is to perform the security check (currently done at the time of filtering a hit from a field in the document), which I obviously cannot do for every possible data value for each user.</p>