Is it possible in solr to specify an ordering of documents

Question

Not a generic sort field, but say a list of document IDs I want returned in that order.

Example: document_ids = [5, 3, 10, 6]

Can I query solr for documents 5, 3, 10, 6 in that order?

Erfert

Answer 1

Using Boost Query

You can use the bq param (Boost Query) for this and then sort by score, which is default.

q=id:5+OR+id:3+OR+id:10+OR+id:6&bq=id:5^4+id:3^3+id:10^2

As you can see within the bq parameter each of the IDs gets a declining boost value, until the last one - in your case 6 - does not receive any boost any more. Since you search by ID, each document would have the same score, so boosting them that way will get you the sort order you want.

Some reference about the parameter

• bq (Boost Query) - Solr Wiki
• The bq Parameter - Reference Guide

Using Term Boosting

In case you are using the Standard Request Handler or the (e)DisMax this works in any case

q=id:5^4+OR+id:3^3+OR+id:10^2+OR+id:6

This makes use of Term Boosting, which is explained in the reference documentation below the topic Boosting a Term with ^. The logic keeps the same as above.

Megrim

This works with (e)dismax, but not with the standard lucene handler. – Terylene

Nice. A simpler syntax is q=id:(5^4 3^3 10^2 6) assuming default Boolean op is OR – Terylene

This didn't work for me. I checked my Solr results in explain.solr.pl and I can see that sometimes lower values such as ^10 gets higher scores than ^19 for instance. In this link wiki.apache.org/solr/SolrRelevancyCookbook#Ranking_Terms we can see it suggests using a very high boost value, but that will lead to huge queries if you need to use a lot of elements. – Clift

Instead of using this, consider using QueryElevationComponent for those use cases. It also allows you to specify the identifiers in query time as param: lucene.apache.org/solr/guide/6_6/…. – Vacuum

@SamuelGarcía I am not working actively with Solr anymore. If you can provide a better solution, please provide an answer. – Megrim

Answer 2

Instead of boosts, Solr supports ConstantScore with the ^= operator. It basically assigns the specified constant score to any matching documents which is desirable when you only care about matches for a particular clause and don’t want other relevancy factors such as term frequency. So you can simply get your desired order by specifying a descending constant score for the ids in the query.

q=id:(id1^=4 OR id2^=3 OR id3^=2 OR id4^=1)

This will assign a constant score of 4 to a document with id=id1 (so it will come first), a score of 3 to a document with id=id2, etc.

Merrile