solrj api for partial document update - solr

Question

Solr 4 beta is out, the GA version will follow soon. Partial document updates has been around for a while as explained here: http://solr.pl/en/2012/07/09/solr-4-0-partial-documents-update/
However, I haven't figured out how to do it with solrj api.
Does anyone knows if it is possible with solrj? Or is solrj just not up-to-speed with this feature?
update: as I describe in the mailing list (see reply here), I found that in the solrj api, the value of a SolrInputField can be a map - it doesn't have to be a simple scalar value.
If it is a map, solrj adds an additional update attribute to the field's xml element.
For example,
This code:
SolrInputDocument doc = new SolrInputDocument();
Map<String, String> partialUpdate = new HashMap<String, String>();
partialUpdate.put("set", "foo");
doc.addField("id", "test_123");
doc.addField("description", partialUpdate);
yields this document:
<doc boost="1.0">
<field name="id">test_123</field>
<field name="description" update="set">foo</field>
</doc>
In this example I used the word "set" for this additional attribute, but it doesn't work.
Solr doesn't update the field as I expected.
According to this link:
http://solr.pl/en/2012/07/09/solr-4-0-partial-documents-update/
valid values are "set" and "add".
Any idea?

Answer 1

As it turns out, the code snippet shown above in the question actually works. I don't know what was wrong the first time I tried it, perhaps I simply forgot to commit or my schema was misconfigured.
In any case, this question is very localized. However, since the api with the hash map is so poorly documented, I thought maybe it is worth to keep this question and answer.
The key of the hash map can be one of three values:
set - to set a field.
add - to add to a multi-valued field.
inc - to increment a field.
There is an example of this code in the solrj unit tests, in a method called testUpdateField.

Answer 2

You can update parts of documents using the SOLR API's update endpoint
curl 'https://solr-url/update?commitWithin=1000&overwrite=true&wt=json' \
-X POST \
-H 'accept: application/json, text/plain, */*' \
--data-raw '[{ "the-unique-filed": "value", "field-to-change":{"set": "new-value"} }]' \
--compressed
Or from UI