SOLR - Grouping results with group.limit return wrong numFound

Question

When I do a search with grouping result and perform group limit, I get that numFound is the same as I when I don’t use the limit.

It looks like SOLR first performs search and calculates numFound and then limit the results.

I can't use pagination and other stuff. Is there any workaround or I missed something ?

---

Example:

======================================
| id |  publisher | book_title      |
======================================
| 1  | A1         | Title Book      |
| 2  | A1         | Book title 123  |
| 3  | A1         | My book         |
| 4  | B2         | Hi book title   |
| 5  | B2         | Another Book    |

If I perform query:

q=book_title:book
&group=true 
&group.field=publisher 
&group.limit=1
&group.main=true 

I will get numFound 5 but only 2 in the results.

"response": {
    "numFound": 5,
    "docs": [
        {
            "book_title": "My book",
            "publisher":  "A1"
        },
        {
            "book_title": "Another Book",
            "publisher":  "B2"
        }
    ]
}

Answer 1

Set group.ngroups to true. That will produce

"grouped": {
"bl_version_id": {
  "matches": 53,
  "ngroups": 18,
  "groups": [
    {
...

Answer 2

I had the same problem, couldn't find a way to fix the root cause, but I will share my solution as a workaround.

What I did is

1. Facet by the field I'm grouping on.
2. Count the number of unique facets. This will match the number of unique documents (2 in your case)

Add these faceting parameters to your query:

&facet=true
&facet.limit=-1
&facet.field=publisher

Notes:

• This is a bit expensive, but it's the only way that worked for me (so far).
• This will only work if publisher is not multi-valued