hydrates federated search

crates/dump/src/lib.rs

@@ -317,6 +317,7 @@ pub(crate) mod test {
                 FilterableAttributesRule::Field(S("race")),
                 FilterableAttributesRule::Field(S("age")),
             ]),
+            foreign_keys: Setting::NotSet,
             sortable_attributes: Setting::Set(btreeset! { S("age") }),
             ranking_rules: Setting::NotSet,
             stop_words: Setting::NotSet,

crates/dump/src/reader/compat/v5_to_v6.rs

@@ -349,6 +349,7 @@ impl<T> From<v5::Settings<T>> for v6::Settings<v6::Unchecked> {
                 v5::settings::Setting::Reset => v6::Setting::Reset,
                 v5::settings::Setting::NotSet => v6::Setting::NotSet,
             },
+            foreign_keys: v6::Setting::NotSet,
             sortable_attributes: settings.sortable_attributes.into(),
             ranking_rules: {
                 match settings.ranking_rules {

crates/index-scheduler/src/features.rs

@@ -171,6 +171,19 @@ impl RoFeatures {
             .into())
         }
     }
+
+    pub fn check_foreign_keys_setting(&self, disabled_action: &'static str) -> Result<()> {
+        if self.runtime.foreign_keys {
+            Ok(())
+        } else {
+            Err(FeatureNotEnabledError {
+                disabled_action,
+                feature: "foreign_keys",
+                issue_link: "https://github.com/orgs/meilisearch/discussions/873",
+            }
+            .into())
+        }
+    }
 }
 
 impl FeatureData {

crates/index-scheduler/src/scheduler/snapshots/test.rs/test_settings_update/after_registering_settings_task.snap

@@ -6,7 +6,7 @@ source: crates/index-scheduler/src/scheduler/test.rs
 []
 ----------------------------------------------------------------------
 ### All Tasks:
-0 {uid: 0, status: enqueued, details: { settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> } }, kind: SettingsUpdate { index_uid: "doggos", new_settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> }, is_deletion: false, allow_index_creation: true }}
+0 {uid: 0, status: enqueued, details: { settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, foreign_keys: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> } }, kind: SettingsUpdate { index_uid: "doggos", new_settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, foreign_keys: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> }, is_deletion: false, allow_index_creation: true }}
 ----------------------------------------------------------------------
 ### Status:
 enqueued [0,]

crates/index-scheduler/src/scheduler/snapshots/test.rs/test_settings_update/settings_update_processed.snap

@@ -6,7 +6,7 @@ source: crates/index-scheduler/src/scheduler/test.rs
 []
 ----------------------------------------------------------------------
 ### All Tasks:
-0 {uid: 0, batch_uid: 0, status: succeeded, details: { settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> } }, kind: SettingsUpdate { index_uid: "doggos", new_settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> }, is_deletion: false, allow_index_creation: true }}
+0 {uid: 0, batch_uid: 0, status: succeeded, details: { settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, foreign_keys: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> } }, kind: SettingsUpdate { index_uid: "doggos", new_settings: Settings { displayed_attributes: WildcardSetting(NotSet), searchable_attributes: WildcardSetting(NotSet), filterable_attributes: NotSet, sortable_attributes: NotSet, foreign_keys: NotSet, ranking_rules: NotSet, stop_words: NotSet, non_separator_tokens: NotSet, separator_tokens: NotSet, dictionary: NotSet, synonyms: NotSet, distinct_attribute: NotSet, proximity_precision: NotSet, typo_tolerance: NotSet, faceting: NotSet, pagination: NotSet, embedders: Set({"default": Set(EmbeddingSettings { source: Set(Rest), model: NotSet, revision: NotSet, pooling: NotSet, api_key: Set("My super secret"), dimensions: Set(4), binary_quantized: NotSet, document_template: NotSet, document_template_max_bytes: NotSet, url: Set("http://localhost:7777"), indexing_fragments: NotSet, search_fragments: NotSet, request: Set(String("{{text}}")), response: Set(String("{{embedding}}")), headers: NotSet, search_embedder: NotSet, indexing_embedder: NotSet, distribution: NotSet })}), search_cutoff_ms: NotSet, localized_attributes: NotSet, facet_search: NotSet, prefix_search: NotSet, chat: NotSet, vector_store: NotSet, _kind: PhantomData<meilisearch_types::settings::Unchecked> }, is_deletion: false, allow_index_creation: true }}
 ----------------------------------------------------------------------
 ### Status:
 enqueued []

crates/meilisearch-types/src/error.rs

@@ -327,6 +327,7 @@ InvalidSettingsFacetSearch                     , InvalidRequest       , BAD_REQU
 InvalidSettingsPrefixSearch                    , InvalidRequest       , BAD_REQUEST ;
 InvalidSettingsFaceting                        , InvalidRequest       , BAD_REQUEST ;
 InvalidSettingsFilterableAttributes            , InvalidRequest       , BAD_REQUEST ;
+InvalidSettingsForeignKeys                     , InvalidRequest       , BAD_REQUEST ;
 InvalidSettingsPagination                      , InvalidRequest       , BAD_REQUEST ;
 InvalidSettingsSearchCutoffMs                  , InvalidRequest       , BAD_REQUEST ;
 InvalidSettingsEmbedders                       , InvalidRequest       , BAD_REQUEST ;

crates/meilisearch-types/src/features.rs

@@ -22,6 +22,7 @@ pub struct RuntimeTogglableFeatures {
     pub chat_completions: bool,
     pub multimodal: bool,
     pub vector_store_setting: bool,
+    pub foreign_keys: bool,
 }
 
 #[derive(Default, Debug, Clone, Copy)]

crates/meilisearch-types/src/settings.rs

@@ -15,7 +15,10 @@ pub use milli::update::ChatSettings;
 use milli::update::Setting;
 use milli::vector::db::IndexEmbeddingConfig;
 use milli::vector::VectorStoreBackend;
-use milli::{Criterion, CriterionError, FilterableAttributesRule, Index, DEFAULT_VALUES_PER_FACET};
+use milli::{
+    Criterion, CriterionError, FilterableAttributesRule, ForeignKey, Index,
+    DEFAULT_VALUES_PER_FACET,
+};
 use serde::{Deserialize, Serialize, Serializer};
 use utoipa::ToSchema;
 
@@ -221,6 +224,12 @@ pub struct Settings<T> {
     #[schema(value_type = Option<Vec<String>>, example = json!(["release_date"]))]
     pub sortable_attributes: Setting<BTreeSet<String>>,
 
+    /// Foreign keys to use for cross-index filtering search.
+    #[serde(default, skip_serializing_if = "Setting::is_not_set")]
+    #[deserr(default, error = DeserrJsonError<InvalidSettingsForeignKeys>)]
+    #[schema(value_type = Option<Vec<ForeignKey>>, example = json!([{"foreignIndexUid": "products", "fieldName": "productId"}]))]
+    pub foreign_keys: Setting<Vec<ForeignKey>>,
+
     /// List of ranking rules sorted by order of importance. The order is customizable.
     /// [A list of ordered built-in ranking rules](https://www.meilisearch.com/docs/learn/relevancy/relevancy).
     #[serde(default, skip_serializing_if = "Setting::is_not_set")]
@@ -376,6 +385,7 @@ impl Settings<Checked> {
             displayed_attributes: Setting::Reset.into(),
             searchable_attributes: Setting::Reset.into(),
             filterable_attributes: Setting::Reset,
+            foreign_keys: Setting::Reset,
             sortable_attributes: Setting::Reset,
             ranking_rules: Setting::Reset,
             stop_words: Setting::Reset,
@@ -404,6 +414,7 @@ impl Settings<Checked> {
             displayed_attributes,
             searchable_attributes,
             filterable_attributes,
+            foreign_keys,
             sortable_attributes,
             ranking_rules,
             stop_words,
@@ -431,6 +442,7 @@ impl Settings<Checked> {
             searchable_attributes,
             filterable_attributes,
             sortable_attributes,
+            foreign_keys,
             ranking_rules,
             stop_words,
             non_separator_tokens,
@@ -482,6 +494,7 @@ impl Settings<Unchecked> {
             displayed_attributes: displayed_attributes.into(),
             searchable_attributes: searchable_attributes.into(),
             filterable_attributes: self.filterable_attributes,
+            foreign_keys: self.foreign_keys,
             sortable_attributes: self.sortable_attributes,
             ranking_rules: self.ranking_rules,
             stop_words: self.stop_words,
@@ -543,6 +556,7 @@ impl Settings<Unchecked> {
                 .sortable_attributes
                 .clone()
                 .or(self.sortable_attributes.clone()),
+            foreign_keys: other.foreign_keys.clone().or(self.foreign_keys.clone()),
             ranking_rules: other.ranking_rules.clone().or(self.ranking_rules.clone()),
             stop_words: other.stop_words.clone().or(self.stop_words.clone()),
             non_separator_tokens: other
@@ -604,6 +618,7 @@ pub fn apply_settings_to_builder(
         searchable_attributes,
         filterable_attributes,
         sortable_attributes,
+        foreign_keys,
         ranking_rules,
         stop_words,
         non_separator_tokens,
@@ -651,6 +666,12 @@ pub fn apply_settings_to_builder(
         Setting::NotSet => (),
     }
 
+    match foreign_keys {
+        Setting::Set(ref keys) => builder.set_foreign_keys(keys.clone().into_iter().collect()),
+        Setting::Reset => builder.reset_foreign_keys(),
+        Setting::NotSet => (),
+    }
+
     match ranking_rules {
         Setting::Set(ref criteria) => {
             builder.set_criteria(criteria.iter().map(|c| c.clone().into()).collect())
@@ -868,6 +889,8 @@ pub fn settings(
 
     let sortable_attributes = index.sortable_fields(rtxn)?.into_iter().collect();
 
+    let foreign_keys = index.foreign_keys(rtxn)?.into_iter().collect();
+
     let criteria = index.criteria(rtxn)?;
 
     let stop_words = index
@@ -965,6 +988,7 @@ pub fn settings(
         .into(),
         filterable_attributes: Setting::Set(filterable_attributes),
         sortable_attributes: Setting::Set(sortable_attributes),
+        foreign_keys: Setting::Set(foreign_keys),
         ranking_rules: Setting::Set(criteria.iter().map(|c| c.clone().into()).collect()),
         stop_words: Setting::Set(stop_words),
         non_separator_tokens: Setting::Set(non_separator_tokens),
@@ -1207,6 +1231,7 @@ pub(crate) mod test {
             searchable_attributes: Setting::Set(vec![String::from("hello")]).into(),
             filterable_attributes: Setting::NotSet,
             sortable_attributes: Setting::NotSet,
+            foreign_keys: Setting::NotSet,
             ranking_rules: Setting::NotSet,
             stop_words: Setting::NotSet,
             non_separator_tokens: Setting::NotSet,
@@ -1240,6 +1265,7 @@ pub(crate) mod test {
                 .into(),
             filterable_attributes: Setting::NotSet,
             sortable_attributes: Setting::NotSet,
+            foreign_keys: Setting::NotSet,
             ranking_rules: Setting::NotSet,
             stop_words: Setting::NotSet,
             non_separator_tokens: Setting::NotSet,

crates/meilisearch/src/analytics/segment_analytics.rs

@@ -208,6 +208,7 @@ struct Infos {
     experimental_no_edition_2024_for_prefix_post_processing: bool,
     experimental_no_edition_2024_for_facet_post_processing: bool,
     experimental_vector_store_setting: bool,
+    experimental_foreign_keys: bool,
     experimental_personalization: bool,
     gpu_enabled: bool,
     db_path: bool,
@@ -317,6 +318,7 @@ impl Infos {
             chat_completions,
             multimodal,
             vector_store_setting,
+            foreign_keys,
         } = features;
 
         // We're going to override every sensible information.
@@ -343,6 +345,7 @@ impl Infos {
             experimental_no_snapshot_compaction,
             experimental_no_edition_2024_for_dumps,
             experimental_vector_store_setting: vector_store_setting,
+            experimental_foreign_keys: foreign_keys,
             gpu_enabled: meilisearch_types::milli::vector::is_cuda_enabled(),
             db_path: db_path != Path::new("./data.ms"),
             import_dump: import_dump.is_some(),

crates/meilisearch/src/routes/features.rs

@@ -56,6 +56,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
             chat_completions: Some(false),
             multimodal: Some(false),
             vector_store_setting: Some(false),
+            foreign_keys: Some(false),
         })),
         (status = 401, description = "The authorization header is missing", body = ResponseError, content_type = "application/json", example = json!(
             {
@@ -106,6 +107,8 @@ pub struct RuntimeTogglableFeatures {
     pub multimodal: Option<bool>,
     #[deserr(default)]
     pub vector_store_setting: Option<bool>,
+    #[deserr(default)]
+    pub foreign_keys: Option<bool>,
 }
 
 impl From<meilisearch_types::features::RuntimeTogglableFeatures> for RuntimeTogglableFeatures {
@@ -121,6 +124,7 @@ impl From<meilisearch_types::features::RuntimeTogglableFeatures> for RuntimeTogg
             chat_completions,
             multimodal,
             vector_store_setting,
+            foreign_keys,
         } = value;
 
         Self {
@@ -134,6 +138,7 @@ impl From<meilisearch_types::features::RuntimeTogglableFeatures> for RuntimeTogg
             chat_completions: Some(chat_completions),
             multimodal: Some(multimodal),
             vector_store_setting: Some(vector_store_setting),
+            foreign_keys: Some(foreign_keys),
         }
     }
 }
@@ -150,6 +155,7 @@ pub struct PatchExperimentalFeatureAnalytics {
     chat_completions: bool,
     multimodal: bool,
     vector_store_setting: bool,
+    foreign_keys: bool,
 }
 
 impl Aggregate for PatchExperimentalFeatureAnalytics {
@@ -169,6 +175,7 @@ impl Aggregate for PatchExperimentalFeatureAnalytics {
             chat_completions: new.chat_completions,
             multimodal: new.multimodal,
             vector_store_setting: new.vector_store_setting,
+            foreign_keys: new.foreign_keys,
         })
     }
 
@@ -197,6 +204,7 @@ impl Aggregate for PatchExperimentalFeatureAnalytics {
             chat_completions: Some(false),
             multimodal: Some(false),
             vector_store_setting: Some(false),
+            foreign_keys: Some(false),
          })),
         (status = 401, description = "The authorization header is missing", body = ResponseError, content_type = "application/json", example = json!(
             {
@@ -244,6 +252,7 @@ async fn patch_features(
             .0
             .vector_store_setting
             .unwrap_or(old_features.vector_store_setting),
+        foreign_keys: new_features.0.foreign_keys.unwrap_or(old_features.foreign_keys),
     };
 
     // explicitly destructure for analytics rather than using the `Serialize` implementation, because
@@ -260,6 +269,7 @@ async fn patch_features(
         chat_completions,
         multimodal,
         vector_store_setting,
+        foreign_keys,
     } = new_features;
 
     analytics.publish(
@@ -274,6 +284,7 @@ async fn patch_features(
             chat_completions,
             multimodal,
             vector_store_setting,
+            foreign_keys,
         },
         &req,
     );

crates/meilisearch/src/routes/indexes/settings.rs

@@ -531,6 +531,17 @@ make_setting_routes!(
         camelcase_attr: "vectorStore",
         analytics: VectorStoreAnalytics
     },
+    {
+        route: "/foreign-keys",
+        update_verb: put,
+        value_type: Vec<meilisearch_types::milli::ForeignKey>,
+        err_type: meilisearch_types::deserr::DeserrJsonError<
+            meilisearch_types::error::deserr_codes::InvalidSettingsForeignKeys,
+        >,
+        attr: foreign_keys,
+        camelcase_attr: "foreignKeys",
+        analytics: ForeignKeysAnalytics
+    },
 );
 
 #[utoipa::path(
@@ -595,6 +606,7 @@ pub async fn update_all(
             filterable_attributes: FilterableAttributesAnalytics::new(
                 new_settings.filterable_attributes.as_ref().set(),
             ),
+            foreign_keys: ForeignKeysAnalytics::new(new_settings.foreign_keys.as_ref().set()),
             distinct_attribute: DistinctAttributeAnalytics::new(
                 new_settings.distinct_attribute.as_ref().set(),
             ),
@@ -688,6 +700,10 @@ pub async fn get_all(
         new_settings.vector_store = Setting::NotSet;
     }
 
+    if features.check_foreign_keys_setting("showing index `foreignKeys` settings").is_err() {
+        new_settings.foreign_keys = Setting::NotSet;
+    }
+
     debug!(returns = ?new_settings, "Get all settings");
     Ok(HttpResponse::Ok().json(new_settings))
 }
@@ -793,5 +809,9 @@ fn validate_settings(
         features.check_vector_store_setting("setting `vectorStore` in the index settings")?;
     }
 
+    if let Setting::Set(_) = &settings.foreign_keys {
+        features.check_foreign_keys_setting("setting `foreignKeys` in the index settings")?;
+    }
+
     Ok(settings.validate()?)
 }

crates/meilisearch/src/routes/indexes/settings_analytics.rs

@@ -9,7 +9,7 @@ use meilisearch_types::facet_values_sort::FacetValuesSort;
 use meilisearch_types::locales::{Locale, LocalizedAttributesRuleView};
 use meilisearch_types::milli::update::Setting;
 use meilisearch_types::milli::vector::VectorStoreBackend;
-use meilisearch_types::milli::FilterableAttributesRule;
+use meilisearch_types::milli::{FilterableAttributesRule, ForeignKey};
 use meilisearch_types::settings::{
     ChatSettings, FacetingSettings, PaginationSettings, PrefixSearchSettings,
     ProximityPrecisionView, RankingRuleView, SettingEmbeddingSettings, TypoSettings,
@@ -25,6 +25,7 @@ pub struct SettingsAnalytics {
     pub displayed_attributes: DisplayedAttributesAnalytics,
     pub sortable_attributes: SortableAttributesAnalytics,
     pub filterable_attributes: FilterableAttributesAnalytics,
+    pub foreign_keys: ForeignKeysAnalytics,
     pub distinct_attribute: DistinctAttributeAnalytics,
     pub proximity_precision: ProximityPrecisionAnalytics,
     pub typo_tolerance: TypoToleranceAnalytics,
@@ -98,6 +99,10 @@ impl Aggregate for SettingsAnalytics {
                     .has_patterns
                     .or(self.filterable_attributes.has_patterns),
             },
+            foreign_keys: ForeignKeysAnalytics {
+                set: new.foreign_keys.set | self.foreign_keys.set,
+                total: new.foreign_keys.total.or(self.foreign_keys.total),
+            },
             distinct_attribute: DistinctAttributeAnalytics {
                 set: self.distinct_attribute.set | new.distinct_attribute.set,
             },
@@ -362,6 +367,22 @@ impl FilterableAttributesAnalytics {
     }
 }
 
+#[derive(Serialize, Default)]
+pub struct ForeignKeysAnalytics {
+    pub set: bool,
+    pub total: Option<usize>,
+}
+
+impl ForeignKeysAnalytics {
+    pub fn new(settings: Option<&Vec<ForeignKey>>) -> Self {
+        Self { set: settings.is_some(), total: settings.as_ref().map(|s| s.len()) }
+    }
+
+    pub fn into_settings(self) -> SettingsAnalytics {
+        SettingsAnalytics { foreign_keys: self, ..Default::default() }
+    }
+}
+
 #[derive(Serialize, Default)]
 pub struct DistinctAttributeAnalytics {
     pub set: bool,

crates/meilisearch/src/search/federated/perform.rs

@@ -10,12 +10,17 @@ use actix_http::StatusCode;
 use index_scheduler::{IndexScheduler, RoFeatures};
 use itertools::Itertools;
 use meilisearch_types::error::ResponseError;
+use meilisearch_types::heed::RoTxn;
 use meilisearch_types::milli::order_by_map::OrderByMap;
 use meilisearch_types::milli::score_details::{ScoreDetails, WeightedScoreValue};
 use meilisearch_types::milli::vector::Embedding;
-use meilisearch_types::milli::{self, DocumentId, OrderBy, TimeBudget, DEFAULT_VALUES_PER_FACET};
+use meilisearch_types::milli::{
+    self, DocumentId, ForeignKey, OrderBy, TimeBudget, DEFAULT_VALUES_PER_FACET,
+};
 use meilisearch_types::network::{Network, Remote};
+use permissive_json_pointer::map_leaf_values;
 use roaring::RoaringBitmap;
+use serde_json::Value;
 use tokio::task::JoinHandle;
 use uuid::Uuid;
 
@@ -1075,7 +1080,7 @@ impl SearchByIndex {
                     },
                 )
                 .collect();
-        let merged_result = merged_result?;
+        let mut merged_result = merged_result?;
         let estimated_total_hits = candidates.len() as usize;
         let facets = facets_by_index
             .map(|facets_by_index| {
@@ -1100,6 +1105,9 @@ impl SearchByIndex {
                 );
                 error
             })?;
+
+        let foreign_keys = index.foreign_keys(&rtxn)?;
+        hydrate_documents(&mut merged_result, &foreign_keys, &params.index_scheduler)?;
         self.results_by_index.push(SearchResultByIndex {
             index: index_uid,
             primary_key,
@@ -1272,3 +1280,87 @@ impl FacetOrder {
         (facet_distribution, facet_stats, facets_by_index)
     }
 }
+
+fn hydrate_documents(
+    documents: &mut Vec<SearchHitByIndex>,
+    foreign_keys: &[ForeignKey],
+    index_scheduler: &IndexScheduler,
+) -> Result<(), ResponseError> {
+    for foreign_key in foreign_keys {
+        let index = index_scheduler.index(&foreign_key.foreign_index_uid)?;
+        let rtxn = index.read_txn()?;
+
+        // TODO: replace with a simpler formatter
+        let attributes_format = AttributesFormat {
+            attributes_to_retrieve: None,
+            retrieve_vectors: RetrieveVectors::Hide,
+            attributes_to_highlight: None,
+            attributes_to_crop: None,
+            crop_length: 0,
+            crop_marker: "".to_string(),
+            highlight_pre_tag: "".to_string(),
+            highlight_post_tag: "".to_string(),
+            show_matches_position: false,
+            sort: None,
+            show_ranking_score: false,
+            show_ranking_score_details: false,
+            locales: None,
+        };
+        let tokenizer = HitMaker::tokenizer(None, None);
+        let formatter_builder =
+            HitMaker::formatter_builder(milli::MatchingWords::default(), tokenizer);
+        let hit_maker = HitMaker::new(&index, &rtxn, attributes_format, formatter_builder)?;
+
+        for document in documents.iter_mut() {
+            let mut res = Ok(());
+            map_leaf_values(
+                &mut document.hit.document,
+                [foreign_key.field_name.as_str()],
+                |_key, _array_indices, value| {
+                    res = hydrate_document_value(
+                        &rtxn,
+                        &hit_maker,
+                        &index.external_documents_ids(),
+                        value,
+                    );
+                },
+            );
+
+            // TODO: Trick to avoid modifying the map_leaf_values signature, we may use a custom map_leaf_values that returns a Result
+            res?;
+        }
+    }
+
+    Ok(())
+}
+
+fn hydrate_document_value(
+    rtxn: &RoTxn,
+    hit_maker: &HitMaker,
+    external_documents_ids: &milli::ExternalDocumentsIds,
+    value: &mut Value,
+) -> Result<(), ResponseError> {
+    match value {
+        Value::String(inner_value) => {
+            let Some(docid) = external_documents_ids.get(rtxn, inner_value)? else {
+                todo!("Document not found")
+            };
+            let SearchHit { document, .. } = hit_maker.make_hit(docid, &[])?;
+            *value = Value::Object(document);
+        }
+        Value::Number(inner_value) => {
+            let Some(docid) = external_documents_ids.get(rtxn, inner_value.to_string())? else {
+                todo!("Document not found")
+            };
+            let SearchHit { document, .. } = hit_maker.make_hit(docid, &[])?;
+            *value = Value::Object(document);
+        }
+        Value::Array(values) => {
+            for value in values {
+                hydrate_document_value(rtxn, hit_maker, external_documents_ids, value)?;
+            }
+        }
+        _ => unreachable!("Invalid foreign key value type: {value:?}"),
+    }
+    Ok(())
+}

crates/meilisearch/tests/dumps/mod.rs

@@ -237,6 +237,7 @@ async fn import_dump_v1_movie_with_settings() {
       "sortableAttributes": [
         "genres"
       ],
+      "foreignKeys": [],
       "rankingRules": [
         "typo",
         "words",
@@ -411,6 +412,7 @@ async fn import_dump_v1_rubygems_with_settings() {
       "sortableAttributes": [
         "version"
       ],
+      "foreignKeys": [],
       "rankingRules": [
         "typo",
         "words",
@@ -740,6 +742,7 @@ async fn import_dump_v2_movie_with_settings() {
         "genres"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "words",
         "typo",
@@ -911,6 +914,7 @@ async fn import_dump_v2_rubygems_with_settings() {
         "version"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "typo",
         "words",
@@ -1240,6 +1244,7 @@ async fn import_dump_v3_movie_with_settings() {
         "genres"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "words",
         "typo",
@@ -1411,6 +1416,7 @@ async fn import_dump_v3_rubygems_with_settings() {
         "version"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "typo",
         "words",
@@ -1740,6 +1746,7 @@ async fn import_dump_v4_movie_with_settings() {
         "genres"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "words",
         "typo",
@@ -1911,6 +1918,7 @@ async fn import_dump_v4_rubygems_with_settings() {
         "version"
       ],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "typo",
         "words",
@@ -2190,7 +2198,8 @@ async fn import_dump_v6_containing_experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 

crates/meilisearch/tests/features/mod.rs

@@ -27,7 +27,8 @@ async fn experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 
@@ -45,7 +46,8 @@ async fn experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 
@@ -63,7 +65,8 @@ async fn experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 
@@ -82,7 +85,8 @@ async fn experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 
@@ -101,7 +105,8 @@ async fn experimental_features() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 }
@@ -127,7 +132,8 @@ async fn experimental_feature_metrics() {
       "compositeEmbedders": false,
       "chatCompletions": false,
       "multimodal": false,
-      "vectorStoreSetting": false
+      "vectorStoreSetting": false,
+      "foreignKeys": false
     }
     "###);
 
@@ -174,7 +180,7 @@ async fn errors() {
     meili_snap::snapshot!(code, @"400 Bad Request");
     meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
     {
-      "message": "Unknown field `NotAFeature`: expected one of `metrics`, `logsRoute`, `editDocumentsByFunction`, `containsFilter`, `network`, `getTaskDocumentsRoute`, `compositeEmbedders`, `chatCompletions`, `multimodal`, `vectorStoreSetting`",
+      "message": "Unknown field `NotAFeature`: expected one of `metrics`, `logsRoute`, `editDocumentsByFunction`, `containsFilter`, `network`, `getTaskDocumentsRoute`, `compositeEmbedders`, `chatCompletions`, `multimodal`, `vectorStoreSetting`, `foreignKeys`",
       "code": "bad_request",
       "type": "invalid_request",
       "link": "https://docs.meilisearch.com/errors#bad_request"

crates/meilisearch/tests/settings/get_settings.rs

@@ -318,6 +318,7 @@ async fn secrets_are_hidden_in_settings() {
       ],
       "filterableAttributes": [],
       "sortableAttributes": [],
+      "foreignKeys": [],
       "rankingRules": [
         "words",
         "typo",

crates/milli/src/index.rs

@@ -53,6 +53,7 @@ pub mod main_key {
     pub const HIDDEN_FACETED_FIELDS_KEY: &str = "hidden-faceted-fields";
     pub const FILTERABLE_FIELDS_KEY: &str = "filterable-fields";
     pub const SORTABLE_FIELDS_KEY: &str = "sortable-fields";
+    pub const FOREIGN_KEYS_KEY: &str = "foreign-keys";
     pub const FIELD_DISTRIBUTION_KEY: &str = "fields-distribution";
     pub const FIELDS_IDS_MAP_KEY: &str = "fields-ids-map";
     pub const FIELDIDS_WEIGHTS_MAP_KEY: &str = "fieldids-weights-map";

crates/milli/src/lib.rs

@@ -19,6 +19,7 @@ mod external_documents_ids;
 pub mod facet;
 mod fields_ids_map;
 mod filterable_attributes_rules;
+mod foreign_key;
 pub mod heed_codec;
 pub mod index;
 mod localized_attributes_rules;
@@ -71,6 +72,7 @@ pub use self::filterable_attributes_rules::{
     FilterFeatures, FilterableAttributesFeatures, FilterableAttributesPatterns,
     FilterableAttributesRule,
 };
+pub use self::foreign_key::ForeignKey;
 pub use self::heed_codec::{
     BEU16StrCodec, BEU32StrCodec, BoRoaringBitmapCodec, BoRoaringBitmapLenCodec,
     CboRoaringBitmapCodec, CboRoaringBitmapLenCodec, FieldIdWordCountCodec, ObkvCodec,

crates/milli/src/update/settings.rs

@@ -45,7 +45,8 @@ use crate::vector::{
     VectorStoreBackend,
 };
 use crate::{
-    ChannelCongestion, FieldId, FilterableAttributesRule, Index, LocalizedAttributesRule, Result,
+    ChannelCongestion, FieldId, FilterableAttributesRule, ForeignKey, Index,
+    LocalizedAttributesRule, Result,
 };
 
 #[derive(Default, Debug, Clone, PartialEq, Eq, Copy)]
@@ -171,6 +172,7 @@ pub struct Settings<'a, 't, 'i> {
     displayed_fields: Setting<Vec<String>>,
     filterable_fields: Setting<Vec<FilterableAttributesRule>>,
     sortable_fields: Setting<HashSet<String>>,
+    foreign_keys: Setting<Vec<ForeignKey>>,
     criteria: Setting<Vec<Criterion>>,
     stop_words: Setting<BTreeSet<String>>,
     non_separator_tokens: Setting<BTreeSet<String>>,
@@ -212,6 +214,7 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
             displayed_fields: Setting::NotSet,
             filterable_fields: Setting::NotSet,
             sortable_fields: Setting::NotSet,
+            foreign_keys: Setting::NotSet,
             criteria: Setting::NotSet,
             stop_words: Setting::NotSet,
             non_separator_tokens: Setting::NotSet,
@@ -273,6 +276,14 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
         self.sortable_fields = Setting::Reset;
     }
 
+    pub fn set_foreign_keys(&mut self, keys: Vec<ForeignKey>) {
+        self.foreign_keys = Setting::Set(keys);
+    }
+
+    pub fn reset_foreign_keys(&mut self) {
+        self.foreign_keys = Setting::Reset;
+    }
+
     pub fn reset_criteria(&mut self) {
         self.criteria = Setting::Reset;
     }
@@ -817,6 +828,19 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
         Ok(())
     }
 
+    fn update_foreign_keys(&mut self) -> Result<()> {
+        match self.foreign_keys {
+            Setting::Set(ref keys) => {
+                self.index.put_foreign_keys(self.wtxn, keys)?;
+            }
+            Setting::Reset => {
+                self.index.delete_foreign_keys(self.wtxn)?;
+            }
+            Setting::NotSet => (),
+        }
+        Ok(())
+    }
+
     fn update_criteria(&mut self) -> Result<()> {
         match &self.criteria {
             Setting::Set(criteria) => {
@@ -1450,6 +1474,7 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
         self.update_sort_facet_values_by()?;
         self.update_pagination_max_total_hits()?;
         self.update_search_cutoff()?;
+        self.update_foreign_keys()?;
 
         // could trigger re-indexing
         self.update_filterable()?;
@@ -1588,6 +1613,7 @@ impl<'a, 't, 'i> Settings<'a, 't, 'i> {
             displayed_fields: Setting::NotSet,
             filterable_fields: Setting::NotSet,
             sortable_fields: Setting::NotSet,
+            foreign_keys: Setting::NotSet,
             criteria: Setting::NotSet,
             stop_words: Setting::NotSet, // TODO (require force reindexing of searchables)
             non_separator_tokens: Setting::NotSet, // TODO (require force reindexing of searchables)

crates/milli/src/update/test_settings.rs

@@ -867,6 +867,7 @@ fn test_correct_settings_init() {
                 displayed_fields,
                 filterable_fields,
                 sortable_fields,
+                foreign_keys,
                 criteria,
                 stop_words,
                 non_separator_tokens,
@@ -897,6 +898,7 @@ fn test_correct_settings_init() {
             assert!(matches!(displayed_fields, Setting::NotSet));
             assert!(matches!(filterable_fields, Setting::NotSet));
             assert!(matches!(sortable_fields, Setting::NotSet));
+            assert!(matches!(foreign_keys, Setting::NotSet));
             assert!(matches!(criteria, Setting::NotSet));
             assert!(matches!(stop_words, Setting::NotSet));
             assert!(matches!(non_separator_tokens, Setting::NotSet));