From 3f3462ab62abbf5d8af7621755ab2b7e87f1ea8c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Renault?= <clement@meilisearch.com>
Date: Wed, 10 Jan 2024 16:34:40 +0100
Subject: [PATCH] Limit the number of values returned by the facet search

---
 meilisearch/src/search.rs                |  3 +++
 meilisearch/tests/search/facet_search.rs | 18 ++++++++++++++++++
 milli/src/search/mod.rs                  | 22 +++++++++++++++++-----
 3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/meilisearch/src/search.rs b/meilisearch/src/search.rs
index b5dba8a58..399c7b95d 100644
--- a/meilisearch/src/search.rs
+++ b/meilisearch/src/search.rs
@@ -735,6 +735,9 @@ pub fn perform_facet_search(
     if let Some(facet_query) = &facet_query {
         facet_search.query(facet_query);
     }
+    if let Some(max_facets) = index.max_values_per_facet(&rtxn)? {
+        facet_search.max_values(max_facets as usize);
+    }
 
     Ok(FacetSearchResult {
         facet_hits: facet_search.execute()?,
diff --git a/meilisearch/tests/search/facet_search.rs b/meilisearch/tests/search/facet_search.rs
index 8c1229f1a..5f9f631f9 100644
--- a/meilisearch/tests/search/facet_search.rs
+++ b/meilisearch/tests/search/facet_search.rs
@@ -105,6 +105,24 @@ async fn more_advanced_facet_search() {
     snapshot!(response["facetHits"].as_array().unwrap().len(), @"1");
 }
 
+#[actix_rt::test]
+async fn simple_facet_search_with_max_values() {
+    let server = Server::new().await;
+    let index = server.index("test");
+
+    let documents = DOCUMENTS.clone();
+    index.update_settings_faceting(json!({ "maxValuesPerFacet": 1 })).await;
+    index.update_settings_filterable_attributes(json!(["genres"])).await;
+    index.add_documents(documents, None).await;
+    index.wait_task(2).await;
+
+    let (response, code) =
+        index.facet_search(json!({"facetName": "genres", "facetQuery": "a"})).await;
+
+    assert_eq!(code, 200, "{}", response);
+    assert_eq!(dbg!(response)["facetHits"].as_array().unwrap().len(), 1);
+}
+
 #[actix_rt::test]
 async fn non_filterable_facet_search_error() {
     let server = Server::new().await;
diff --git a/milli/src/search/mod.rs b/milli/src/search/mod.rs
index 3e4849578..7bac5ea0c 100644
--- a/milli/src/search/mod.rs
+++ b/milli/src/search/mod.rs
@@ -27,8 +27,8 @@ static LEVDIST0: Lazy<LevBuilder> = Lazy::new(|| LevBuilder::new(0, true));
 static LEVDIST1: Lazy<LevBuilder> = Lazy::new(|| LevBuilder::new(1, true));
 static LEVDIST2: Lazy<LevBuilder> = Lazy::new(|| LevBuilder::new(2, true));
 
-/// The maximum number of facets returned by the facet search route.
-const MAX_NUMBER_OF_FACETS: usize = 100;
+/// The maximum number of values per facet returned by the facet search route.
+const DEFAULT_MAX_NUMBER_OF_VALUES_PER_FACET: usize = 100;
 
 pub mod facet;
 mod fst_utils;
@@ -306,6 +306,7 @@ pub struct SearchForFacetValues<'a> {
     query: Option<String>,
     facet: String,
     search_query: Search<'a>,
+    max_values: usize,
     is_hybrid: bool,
 }
 
@@ -315,7 +316,13 @@ impl<'a> SearchForFacetValues<'a> {
         search_query: Search<'a>,
         is_hybrid: bool,
     ) -> SearchForFacetValues<'a> {
-        SearchForFacetValues { query: None, facet, search_query, is_hybrid }
+        SearchForFacetValues {
+            query: None,
+            facet,
+            search_query,
+            max_values: DEFAULT_MAX_NUMBER_OF_VALUES_PER_FACET,
+            is_hybrid,
+        }
     }
 
     pub fn query(&mut self, query: impl Into<String>) -> &mut Self {
@@ -323,6 +330,11 @@ impl<'a> SearchForFacetValues<'a> {
         self
     }
 
+    pub fn max_values(&mut self, max: usize) -> &mut Self {
+        self.max_values = max;
+        self
+    }
+
     fn one_original_value_of(
         &self,
         field_id: FieldId,
@@ -462,7 +474,7 @@ impl<'a> SearchForFacetValues<'a> {
                             .unwrap_or_else(|| left_bound.to_string());
                         results.push(FacetValueHit { value, count });
                     }
-                    if results.len() >= MAX_NUMBER_OF_FACETS {
+                    if results.len() >= self.max_values {
                         break;
                     }
                 }
@@ -507,7 +519,7 @@ impl<'a> SearchForFacetValues<'a> {
                     .unwrap_or_else(|| query.to_string());
                 results.push(FacetValueHit { value, count });
             }
-            if results.len() >= MAX_NUMBER_OF_FACETS {
+            if results.len() >= self.max_values {
                 return Ok(ControlFlow::Break(()));
             }
         }