Solrj: getting MoreLikeThis as beans

Question

Using Solrj it is possible to read Documents from a QueryResponse as (annotated) beans:

List<Item> items = queryResponse.getBeans(Item.class)  

Where Item is the annotated class that maps to a Solr Document.

Now I query for a single document and ask for 10 MoreLikeThis documents:

?q=id:AZ133007&mlt=true&mlt.fl=technique,subject&mlt.mindf=1&mlt.mintf=1&mlt.count=10

This returns the document with id AZ133007 together with 10 'MoreLikeThis' documents (i.e. more like AZ133007 with regard to fields 'technique' and 'subject'). See the (simplified) response below:

<response>

<lst name="responseHeader">
    ...
</lst>

<result name="response" numFound="1" start="0">

    <doc>
        <str name="id">AZ133007</str>
        <str name="title">Still I</str>
        <str name="artist">A.R. Tist</str>
        <str name="technique">Watercolor</str>
        <str name="subject">Still life</str>
    </doc>

</result>

<lst name="moreLikeThis">

    <result name="AZ133007" numFound="84" start="0">

        <doc>
            <str name="id">AZ002001</str>
            <str name="title">Cubes</str>
            <str name="artist">John Doe</str>
            <str name="technique">Watercolor</str>
            <str name="subject">Landscape</str>
        </doc>

        <doc>
            <str name="id">AZ002002</str>
            <str name="title">Cats and Dogs</str>
            <str name="artist">A. Nothername</str>
            <str name="technique">Watercolor</str>
            <str name="subject">Cityscape</str>
        </doc>

        ...

    </result>

</lst>

</response>

The requested document AZ133007 in the response section can be returned as an Item bean like so:

Item item = queryResponse.getBeans(Item.class).get(0);

But how do I get the documents listed under 'moreLikeThis' as beans?

Answer 1

After a lot of experimenting, browsing the web and digging into the Solrj API I came with the following solution. There may be better ways to do it, I would really like to know.

First extract the moreLikeThis section from the response and cast it to a NamedList:

NamedList mlt = (NamedList) queryResponse.getResponse().get("moreLikeThis");

Inspecting the NamedList mlt while debugging, it shows the AZ133007 entry along with the SolrDocuments that are 'moreLikeThis'.

{
    AZ133007={
        numFound=295,
        start=0,
        docs=[
            SolrDocument{
                id=AZ002001,
                title=Cubes,
                artist=JohnDoe,
                technique=Watercolor,
                subject=Landscape
            },
            SolrDocument{
                id=AZ002002,
                title=CatsAndDogs,
                artist=A.Nothername,
                technique=Watercolor,
                subject=Cityscape
            },

            ...

        ]
     }
  }

Now get a SolrDocumentList providing the id:

SolrDocumentList mltDocList = (SolrDocumentList) mlt.get("AZ133007");

And bind this SolrDocumentList to beans:

DocumentObjectBinder b = new DocumentObjectBinder();
List<Item> similarItems = b.getBeans(Item.class, mltDocList);

Of course I didn't hard-code the id and I'd built in some null checks, but you get the idea.