Solr boost query by field value and inside newest date

We have the following setup in our schema.xml:

<field name="last_modified" type="date" indexed="true" stored="true" multiValued="false" omitTermFreqAndPositions="true"/>
...

<field name="prefix" type="string" indexed="true" stored="true" omitTermFreqAndPositions="true"/>

Our goal is to sort the docs by

1. prefix=9999 with newest docs (last modified) first
2. prefix=1004 or prefix=1005 with newest docs (last modified) first

Our code:

{!boost b=recip(ms(NOW,last_modified),3.16e11,1,1)}prefix:9999^1000000 OR {!boost b=recip(ms(NOW,last_modified),3.16e-11,1,1)}prefix:1004^600000 OR {!boost b=recip(ms(NOW,last_modified),3.16e-11,1,1)}prefix:1005^600000

Result: The query above does not work as expected!

We thought that omitTermFreqAndPositions=true will force to prevent ITF and the scoring should work. But it does not seem so! Please help us with this :-)

So we found a solution!

1. Create your own Similarity (a simple java class) For a better and simpler descriptions how, please read How to compile a custom similarity class for SOLR / Lucene using Eclipse

The class we used

package com.luxactive;
import org.apache.lucene.index.FieldInvertState;
import org.apache.lucene.search.similarities.DefaultSimilarity;

public class MyNewSimilarityClass  extends DefaultSimilarity {

@Override
public float coord(int overlap, int maxOverlap) {
    return 1.0f;
}

@Override
public float idf(long docFreq, long numDocs) {
    return 1.0f;
}

@Override
public float lengthNorm(FieldInvertState arg0) {
    return 1.0f;
}

@Override
public float tf(float freq) {
    return 1.0f;
}

}

2. Create a simple jar with your Similarity
3. Copy the jar to any folder into your solr server, we used: SOLRFOLDER/solr-4.8.0/example/solr/dih

The next steps need to be done to every collection you have!

4. Edit the solrconfig.xml at: SOLRFOLDER/solr-4.8.0/example/solr/collection/conf/solrconfig.xml
   Add <lib dir="../dih" regex=".*\.jar" /> to import the custom jar
5. Edit the schema.xml in the same folder

Add the following

<!-- DEFAULT Factory for custom com.luxactive.MyNewSimilarityClass  -->
<similarity class="solr.SchemaSimilarityFactory"/>

<!-- TYPE String -->
 <fieldType name="no_term_frequency_string" class="solr.StrField" sortMissingLast="true" >
    <similarity class="com.luxactive.MyNewSimilarityClass"/>
</fieldType>

<!-- TYPE Date -->
<fieldType name="no_term_frequency_date" class="solr.TrieDateField" sortMissingLast="true" >
    <similarity class="com.luxactive.MyNewSimilarityClass"/>
</fieldType>

<!-- TYPE Int-->
<fieldType name="no_term_frequency_int" class="solr.TrieIntField" sortMissingLast="true" >
    <similarity class="com.luxactive.MyNewSimilarityClass"/>
</fieldType>

Here you define your own field types (int, string and date) that use the new Similarity class which will return a boost value like defined in the MyNewSimilarityClass.

6. Now edit the fields you want to use your custom Similaritry by setting theyr type to one you created.
   From: <field name="last_modified" type="date" indexed="true" stored="true" multiValued="false" />
   To: <field name="last_modified" type="no_term_frequency_date" indexed="true" stored="true" multiValued="false" />
7. Restart the solr server and enjoy your boosting :)