The Extended DisMax (eDismax) Query Parser

Extended DisMax Parameters

In addition to all the DisMax parameters, Extended DisMax includes these query parameters:

These two examples are equivalent:

q={!edismax qf=name}ipod
boost=div(1,sum(1,price))

q={!boost b=div(1,sum(1,price)) v=$qq}
qq={!edismax qf=name}ipod

Examples of eDismax Queries

All of the sample URLs in this section assume you are running Solr’s “techproducts” example:

bin/solr -e techproducts

Boost the result of the query term "hello" based on the document’s popularity:

http://localhost:8983/solr/techproducts/select?defType=edismax&q=hello&pf=text&qf=text&boost=popularity

Search for iPods OR video:

http://localhost:8983/solr/techproducts/select?defType=edismax&q=ipod+OR+video

Search across multiple fields, specifying (via boosts) how important each field is relative each other:

http://localhost:8983/solr/techproducts/select?q=video&defType=edismax&qf=features^20.0+text^0.3

You can boost results that have a field that matches a specific value:

http://localhost:8983/solr/techproducts/select?q=video&defType=edismax&qf=features^20.0+text^0.3&bq=cat:electronics^5.0

Using the mm parameter, 1 and 2 word queries require that all of the optional clauses match, but for queries with three or more clauses one missing clause is allowed:

http://localhost:8983/solr/techproducts/select?q=belkin+ipod&defType=edismax&mm=2
http://localhost:8983/solr/techproducts/select?q=belkin+ipod+gibberish&defType=edismax&mm=2
http://localhost:8983/solr/techproducts/select?q=belkin+ipod+apple&defType=edismax&mm=2

In the example below, we see a per-field override of the qf parameter being used to alias "name" in the query string to either the “last_name” and “first_name” fields:

defType=edismax
q=sysadmin name:Mike
qf=title text last_name first_name
f.name.qf=last_name first_name

Using 'Slop'

Dismax and Edismax can run queries against all query fields, and also run a query in the form of a phrase against the phrase fields. (This will work only for boosting documents, not actually for matching.) However, that phrase query can have a 'slop,' which is the distance between the terms of the query while still considering it a phrase match. For example:

q=foo bar
qf=field1^5 field2^10
pf=field1^50 field2^20
defType=dismax

With these parameters, the Dismax Query Parser generates a query that looks something like this:

 (+(field1:foo^5 OR field2:foo^10) AND (field1:bar^5 OR field2:bar^10))

But it also generates another query that will only be used for boosting results:

field1:"foo bar"^50 OR field2:"foo bar"^20

Thus, any document that has the terms "foo" and "bar" will match; however if some of those documents have both of the terms as a phrase, it will score much higher because it’s more relevant.

If you add the parameter ps (phrase slop), the second query will instead be:

ps=10 field1:"foo bar"~10^50 OR field2:"foo bar"~10^20

This means that if the terms "foo" and "bar" appear in the document with less than 10 terms between each other, the phrase will match. For example the doc that says:

*Foo* term1 term2 term3 *bar*

will match the phrase query.

How does one use phrase slop? Usually it is configured in the request handler (in solrconfig).

With query slop (qs) the concept is similar, but it applies to explicit phrase queries from the user. For example, if you want to search for a name, you could enter:

q="Hans Anderson"

A document that contains "Hans Anderson" will match, but a document that contains the middle name "Christian" or where the name is written with the last name first ("Anderson, Hans") won’t. For those cases one could configure the query field qs, so that even if the user searches for an explicit phrase query, a slop is applied.

Finally, in addition to the phrase fields (pf) parameter, edismax also supports the pf2 and pf3 parameters, for fields over which to create bigram and trigram phrase queries. The phrase slop for these parameters' queries can be specified using the ps2 and ps3 parameters, respectively. If you use pf2/pf3 but not ps2/ps3, then the phrase slop for these parameters' queries will be taken from the ps parameter, if any.