perf(nextcloud): batch oc:fileid resolution to kill PROPFIND N+1

Resolving the stable numeric oc:fileid for every child in a NextCloud
listing issued one `INSERT ... ON CONFLICT DO UPDATE` per entry — a write
(row rewrite + WAL + dead tuple) even when the mapping already existed.
A Depth:1 PROPFIND of a folder with N children meant N sequential write
round-trips on a read-only operation that sync clients repeat constantly.

- Repository: replace the single `get_or_create` (DO UPDATE) with
  `get_or_create_many` — one idempotent bulk `INSERT ... SELECT unnest(...)
  ON CONFLICT DO NOTHING` (existing rows untouched) plus a single
  `SELECT ... WHERE object_id = ANY(...)`. Two statements instead of N.
- Service: add an Arc-backed moka cache (uuid -> i64; the mapping is
  immutable, so warm entries never go stale) and batch APIs
  `get_or_create_file_ids` / `get_or_create_folder_ids` that only query
  the misses. Warm listings cost zero queries.
- Handlers (PROPFIND, REPORT favorites/search, trashbin, OCS unified
  search): pre-resolve all ids in two batched queries — file and folder
  run concurrently via `tokio::join!` — and turn the XML/JSON emission
  into a synchronous map lookup.

https://claude.ai/code/session_01Dp3oWon5GBMVn4j3QXZdgx

src/application/services/nextcloud_file_id_service.rs

@@ -1,12 +1,25 @@
+use std::collections::HashMap;
 use std::sync::Arc;
 
+use moka::future::Cache;
+use uuid::Uuid;
+
 use crate::common::errors::{DomainError, ErrorKind, Result};
 use crate::infrastructure::repositories::pg::NextcloudObjectIdRepository;
 
+/// Capacity of the in-memory UUID→numeric-id cache. The mapping is immutable
+/// once created, so a warm entry never goes stale and eviction only costs a
+/// re-query; ~100k entries is a few MB.
+const ID_CACHE_CAPACITY: u64 = 100_000;
+
 #[derive(Clone)]
 pub struct NextcloudFileIdService {
     repo: Option<Arc<NextcloudObjectIdRepository>>,
     instance_id: String,
+    /// Object-UUID → stable numeric id. `moka` caches are `Arc`-backed, so all
+    /// clones of the service share one cache and the per-child resolution in a
+    /// listing costs zero queries once warm.
+    cache: Cache<Uuid, i64>,
 }
 
 impl NextcloudFileIdService {
@@ -14,6 +27,7 @@ impl NextcloudFileIdService {
         Self {
             repo: Some(repo),
             instance_id,
+            cache: Cache::new(ID_CACHE_CAPACITY),
         }
     }
 
@@ -21,29 +35,76 @@ impl NextcloudFileIdService {
         Self {
             repo: None,
             instance_id: "ocnca".to_string(),
+            cache: Cache::new(ID_CACHE_CAPACITY),
         }
     }
 
-    pub async fn get_or_create_file_id(&self, file_id: &str) -> Result<i64> {
-        let repo = self.repo.as_ref().ok_or_else(|| {
-            DomainError::internal_error("NextcloudFileId", "Repository not initialized")
-        })?;
-        repo.get_or_create("file", file_id).await
+    /// Resolve — creating when absent — stable numeric file IDs for many
+    /// UUIDs at once. Cache hits cost nothing; the misses are resolved with a
+    /// single backing query. The returned map is keyed by the caller's
+    /// original id strings; unresolvable inputs are simply absent (mirroring
+    /// the `.ok()` behaviour the callers relied on).
+    pub async fn get_or_create_file_ids(
+        &self,
+        file_ids: &[String],
+    ) -> Result<HashMap<String, i64>> {
+        self.get_or_create_many("file", file_ids).await
     }
 
-    pub async fn get_or_create_folder_id(&self, folder_id: &str) -> Result<i64> {
-        let repo = self.repo.as_ref().ok_or_else(|| {
+    /// Folder counterpart of [`Self::get_or_create_file_ids`].
+    pub async fn get_or_create_folder_ids(
+        &self,
+        folder_ids: &[String],
+    ) -> Result<HashMap<String, i64>> {
+        self.get_or_create_many("folder", folder_ids).await
+    }
+
+    async fn get_or_create_many(
+        &self,
+        object_type: &str,
+        raw_ids: &[String],
+    ) -> Result<HashMap<String, i64>> {
+        let mut result = HashMap::with_capacity(raw_ids.len());
+        // Parsed-UUID → caller's original string; also dedupes the miss list.
+        let mut pending: HashMap<Uuid, String> = HashMap::new();
+
+        for raw in raw_ids {
+            let Ok(uuid) = Uuid::parse_str(raw) else {
+                continue; // Unparseable ids never had a mapping — skip silently.
+            };
+            if let Some(id) = self.cache.get(&uuid).await {
+                result.insert(raw.clone(), id);
+            } else {
+                pending.entry(uuid).or_insert_with(|| raw.clone());
+            }
+        }
+
+        if !pending.is_empty() {
+            let misses: Vec<Uuid> = pending.keys().copied().collect();
+            let resolved = self
+                .repo()?
+                .get_or_create_many(object_type, &misses)
+                .await?;
+            for (uuid, id) in resolved {
+                self.cache.insert(uuid, id).await;
+                if let Some(original) = pending.get(&uuid) {
+                    result.insert(original.clone(), id);
+                }
+            }
+        }
+
+        Ok(result)
+    }
+
+    fn repo(&self) -> Result<&Arc<NextcloudObjectIdRepository>> {
+        self.repo.as_ref().ok_or_else(|| {
             DomainError::internal_error("NextcloudFileId", "Repository not initialized")
-        })?;
-        repo.get_or_create("folder", folder_id).await
+        })
     }
 
     /// Get the OxiCloud file UUID from a Nextcloud numeric ID.
     pub async fn get_oxicloud_id(&self, nc_file_id: i64) -> Result<String> {
-        let repo = self.repo.as_ref().ok_or_else(|| {
-            DomainError::internal_error("NextcloudFileId", "Repository not initialized")
-        })?;
-        repo.get_object_id(nc_file_id, "file").await
+        self.repo()?.get_object_id(nc_file_id, "file").await
     }
 
     pub fn format_oc_id(&self, id: i64) -> String {
@@ -59,6 +120,7 @@ impl NextcloudFileIdService {
         Self {
             repo: None,
             instance_id: instance_id.to_string(),
+            cache: Cache::new(ID_CACHE_CAPACITY),
         }
     }
 
@@ -107,4 +169,25 @@ mod tests {
         let svc = NextcloudFileIdService::new_stub();
         assert!(svc.ensure_ready().is_err());
     }
+
+    // Empty input resolves to an empty map without ever touching the repo, so
+    // it succeeds even on the repo-less stub.
+    #[tokio::test]
+    async fn test_get_or_create_file_ids_empty_is_noop() {
+        let svc = NextcloudFileIdService::new_stub();
+        let map = svc.get_or_create_file_ids(&[]).await.unwrap();
+        assert!(map.is_empty());
+    }
+
+    // Unparseable ids never had a mapping, so they are skipped before any repo
+    // call — the stub (no repo) must not error on them.
+    #[tokio::test]
+    async fn test_get_or_create_file_ids_skips_unparseable() {
+        let svc = NextcloudFileIdService::new_stub();
+        let map = svc
+            .get_or_create_file_ids(&["not-a-uuid".to_string()])
+            .await
+            .unwrap();
+        assert!(map.is_empty());
+    }
 }

src/infrastructure/repositories/pg/nextcloud_object_id_repository.rs

@@ -1,5 +1,7 @@
 use sqlx::{PgPool, Row};
+use std::collections::HashMap;
 use std::sync::Arc;
+use uuid::Uuid;
 
 use crate::common::errors::{DomainError, ErrorKind, Result};
 
@@ -12,29 +14,73 @@ impl NextcloudObjectIdRepository {
         Self { pool }
     }
 
-    pub async fn get_or_create(&self, object_type: &str, object_id: &str) -> Result<i64> {
-        let row = sqlx::query(
+    /// Resolve — creating when absent — stable numeric IDs for a batch of
+    /// object UUIDs sharing one `object_type`.
+    ///
+    /// Two statements instead of one per id: an idempotent bulk insert that
+    /// leaves existing rows untouched (`ON CONFLICT DO NOTHING` — no row
+    /// rewrite, no WAL churn, no dead tuples, unlike the former `DO UPDATE`),
+    /// followed by a single read of every requested mapping. The insert
+    /// auto-commits before the read, so the read observes both our own rows
+    /// and any created concurrently. Returns a map keyed by object UUID;
+    /// unresolvable inputs are simply absent.
+    pub async fn get_or_create_many(
+        &self,
+        object_type: &str,
+        object_ids: &[Uuid],
+    ) -> Result<HashMap<Uuid, i64>> {
+        if object_ids.is_empty() {
+            return Ok(HashMap::new());
+        }
+
+        // 1. Create missing mappings only. `DO NOTHING` skips the write for
+        //    UUIDs that already map, eliminating the per-listing row rewrite.
+        sqlx::query(
             r#"
             INSERT INTO storage.nextcloud_object_ids (object_type, object_id)
-            VALUES ($1, $2::uuid)
-            ON CONFLICT (object_type, object_id)
-            DO UPDATE SET object_id = EXCLUDED.object_id
-            RETURNING id
+            SELECT $1, u FROM unnest($2::uuid[]) AS u
+            ON CONFLICT (object_type, object_id) DO NOTHING
             "#,
         )
         .bind(object_type)
-        .bind(object_id)
-        .fetch_one(&*self.pool)
+        .bind(object_ids)
+        .execute(&*self.pool)
         .await
         .map_err(|e| {
             DomainError::new(
                 ErrorKind::DatabaseError,
                 "NextcloudFileId",
-                format!("Failed to get/create Nextcloud ID: {}", e),
+                format!("Failed to create Nextcloud IDs: {}", e),
             )
         })?;
 
-        Ok(row.get::<i64, _>("id"))
+        // 2. Read every requested mapping back in a single round-trip.
+        let rows = sqlx::query(
+            r#"
+            SELECT id, object_id
+            FROM storage.nextcloud_object_ids
+            WHERE object_type = $1 AND object_id = ANY($2::uuid[])
+            "#,
+        )
+        .bind(object_type)
+        .bind(object_ids)
+        .fetch_all(&*self.pool)
+        .await
+        .map_err(|e| {
+            DomainError::new(
+                ErrorKind::DatabaseError,
+                "NextcloudFileId",
+                format!("Failed to load Nextcloud IDs: {}", e),
+            )
+        })?;
+
+        let mut map = HashMap::with_capacity(rows.len());
+        for row in rows {
+            let object_id: Uuid = row.get("object_id");
+            let id: i64 = row.get("id");
+            map.insert(object_id, id);
+        }
+        Ok(map)
     }
 
     /// Get the OxiCloud object ID from a Nextcloud numeric ID.

src/interfaces/nextcloud/ocs_handler.rs

@@ -5,6 +5,7 @@ use axum::{
     response::{IntoResponse, Response},
 };
 use serde_json::json;
+use std::collections::HashMap;
 use std::sync::Arc;
 
 use crate::application::dtos::search_dto::SearchCriteriaDto;
@@ -384,6 +385,17 @@ pub async fn handle_search(
 
     let file_id_svc = state.nextcloud.as_ref().map(|n| &n.file_ids);
 
+    // Pre-resolve numeric ids for every file result in a single batch query
+    // (was one INSERT round-trip per result).
+    let file_uuids: Vec<String> = results.files.iter().map(|f| f.id.clone()).collect();
+    let file_id_map: HashMap<String, i64> = match file_id_svc {
+        Some(svc) => svc
+            .get_or_create_file_ids(&file_uuids)
+            .await
+            .unwrap_or_default(),
+        None => HashMap::new(),
+    };
+
     let mut entries: Vec<serde_json::Value> = Vec::new();
 
     // Map file results
@@ -394,11 +406,7 @@ pub async fn handle_search(
             .unwrap_or(&file.path);
         let display_path = format!("/{}", display_path);
 
-        let numeric_id = if let Some(svc) = file_id_svc {
-            svc.get_or_create_file_id(&file.id).await.ok()
-        } else {
-            None
-        };
+        let numeric_id = file_id_map.get(&file.id).copied();
 
         let thumbnail_url = match numeric_id {
             Some(nid) => format!("/index.php/core/preview?fileId={}&x=32&y=32", nid),

src/interfaces/nextcloud/report_handler.rs

@@ -25,8 +25,7 @@ use crate::domain::entities::file::File;
 use crate::interfaces::errors::AppError;
 use crate::interfaces::middleware::auth::CurrentUser;
 use crate::interfaces::nextcloud::webdav_handler::{
-    format_oc_id, nc_href, resolve_file_id, resolve_folder_id, write_file_response,
-    write_folder_response,
+    batch_resolve_ids, format_oc_id, nc_href, write_file_response, write_folder_response,
 };
 
 /// Handle WebDAV REPORT and SEARCH methods for Nextcloud compatibility.
@@ -87,56 +86,71 @@ async fn handle_filter_files(
 
     let home_prefix = format!("My Folder - {}/", user.username);
 
+    // Pass 1: fetch the favorited DTOs (the per-item fetch is a separate
+    // concern from the oc:fileid resolution batched below).
+    let mut files: Vec<FileDto> = Vec::new();
+    let mut folders: Vec<FolderDto> = Vec::new();
+    for fav in &favorites {
+        match fav.item_type.as_str() {
+            "file" => {
+                if let Ok(f) = file_service.get_file(&fav.item_id).await {
+                    files.push(f);
+                }
+            }
+            "folder" => {
+                if let Ok(f) = folder_service.get_folder(&fav.item_id).await {
+                    folders.push(f);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    // Pass 2: resolve every oc:fileid in two batch queries (was one per item).
+    let file_uuids: Vec<String> = files.iter().map(|f| f.id.clone()).collect();
+    let folder_uuids: Vec<String> = folders.iter().map(|f| f.id.clone()).collect();
+    let (file_id_map, folder_id_map) =
+        batch_resolve_ids(file_id_svc, &file_uuids, &folder_uuids).await;
+
+    // Pass 3: write the multistatus XML (pure synchronous map lookups).
     let mut buf = Vec::new();
     {
         let mut xml = Writer::new(&mut buf);
 
         write_multistatus_start(&mut xml)?;
 
-        for fav in &favorites {
-            match fav.item_type.as_str() {
-                "file" => {
-                    let file = match file_service.get_file(&fav.item_id).await {
-                        Ok(f) => f,
-                        Err(_) => continue, // Deleted or inaccessible -- skip.
-                    };
-                    let subpath = strip_home_prefix(&file.path, &home_prefix);
-                    let href = nc_href(&user.username, subpath);
-                    let fid = resolve_file_id(file_id_svc, &file.id).await;
-                    let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
-                    write_file_response(
-                        &mut xml,
-                        &file,
-                        &href,
-                        fid,
-                        oc_id.as_deref(),
-                        &user.username,
-                        &favorite_ids,
-                    )
-                    .map_err(|e| AppError::internal_error(format!("XML write error: {}", e)))?;
-                }
-                "folder" => {
-                    let folder = match folder_service.get_folder(&fav.item_id).await {
-                        Ok(f) => f,
-                        Err(_) => continue,
-                    };
-                    let subpath = strip_home_prefix(&folder.path, &home_prefix);
-                    let href = format!("{}/", nc_href(&user.username, subpath));
-                    let fid = resolve_folder_id(file_id_svc, &folder.id).await;
-                    let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
-                    write_folder_response(
-                        &mut xml,
-                        &folder,
-                        &href,
-                        fid,
-                        oc_id.as_deref(),
-                        &user.username,
-                        &favorite_ids,
-                    )
-                    .map_err(|e| AppError::internal_error(format!("XML write error: {}", e)))?;
-                }
-                _ => continue,
-            }
+        for file in &files {
+            let subpath = strip_home_prefix(&file.path, &home_prefix);
+            let href = nc_href(&user.username, subpath);
+            let fid = file_id_map.get(&file.id).copied();
+            let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
+            write_file_response(
+                &mut xml,
+                file,
+                &href,
+                fid,
+                oc_id.as_deref(),
+                &user.username,
+                &favorite_ids,
+            )
+            .map_err(|e| AppError::internal_error(format!("XML write error: {}", e)))?;
+        }
+
+        for folder in &folders {
+            let subpath = strip_home_prefix(&folder.path, &home_prefix);
+            let href = format!("{}/", nc_href(&user.username, subpath));
+            let fid = folder_id_map.get(&folder.id).copied();
+            let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
+            write_folder_response(
+                &mut xml,
+                folder,
+                &href,
+                fid,
+                oc_id.as_deref(),
+                &user.username,
+                &favorite_ids,
+            )
+            .map_err(|e| AppError::internal_error(format!("XML write error: {}", e)))?;
         }
 
         xml.write_event(Event::End(BytesEnd::new("d:multistatus")))
@@ -192,6 +206,15 @@ async fn handle_search(
     // No favorite checking for search results -- pass an empty set.
     let favorite_ids: HashSet<String> = HashSet::new();
 
+    // Materialize DTOs, then resolve every oc:fileid in two batch queries
+    // (was one INSERT round-trip per result).
+    let files: Vec<FileDto> = results.files.iter().map(file_dto_from_search).collect();
+    let folders: Vec<FolderDto> = results.folders.iter().map(folder_dto_from_search).collect();
+    let file_uuids: Vec<String> = files.iter().map(|f| f.id.clone()).collect();
+    let folder_uuids: Vec<String> = folders.iter().map(|f| f.id.clone()).collect();
+    let (file_id_map, folder_id_map) =
+        batch_resolve_ids(file_id_svc, &file_uuids, &folder_uuids).await;
+
     let mut buf = Vec::new();
     {
         let mut xml = Writer::new(&mut buf);
@@ -199,15 +222,14 @@ async fn handle_search(
         write_multistatus_start(&mut xml)?;
 
         // Files.
-        for fr in &results.files {
-            let file = file_dto_from_search(fr);
+        for file in &files {
             let subpath = strip_home_prefix(&file.path, &home_prefix);
             let href = nc_href(&user.username, subpath);
-            let fid = resolve_file_id(file_id_svc, &file.id).await;
+            let fid = file_id_map.get(&file.id).copied();
             let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
             write_file_response(
                 &mut xml,
-                &file,
+                file,
                 &href,
                 fid,
                 oc_id.as_deref(),
@@ -218,15 +240,14 @@ async fn handle_search(
         }
 
         // Folders.
-        for sr in &results.folders {
-            let folder = folder_dto_from_search(sr);
+        for folder in &folders {
             let subpath = strip_home_prefix(&folder.path, &home_prefix);
             let href = format!("{}/", nc_href(&user.username, subpath));
-            let fid = resolve_folder_id(file_id_svc, &folder.id).await;
+            let fid = folder_id_map.get(&folder.id).copied();
             let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));
             write_folder_response(
                 &mut xml,
-                &folder,
+                folder,
                 &href,
                 fid,
                 oc_id.as_deref(),

src/interfaces/nextcloud/trashbin_handler.rs

@@ -14,7 +14,7 @@ use crate::common::di::AppState;
 use crate::interfaces::errors::AppError;
 use crate::interfaces::middleware::auth::{AuthUser, CurrentUser};
 use crate::interfaces::nextcloud::webdav_handler::{
-    format_oc_id, resolve_file_id, resolve_folder_id, write_text_element,
+    batch_resolve_ids, format_oc_id, write_text_element,
 };
 
 const HEADER_DAV: HeaderName = HeaderName::from_static("dav");
@@ -198,6 +198,7 @@ fn strip_home_prefix<'a>(original_path: &'a str, username: &str) -> &'a str {
 
 use crate::application::dtos::trash_dto::TrashedItemDto;
 use crate::application::services::nextcloud_file_id_service::NextcloudFileIdService;
+use std::collections::HashMap;
 
 /// Generate a complete Nextcloud-compatible multistatus XML response for the trashbin.
 async fn write_trashbin_multistatus<W: std::io::Write>(
@@ -219,9 +220,25 @@ async fn write_trashbin_multistatus<W: std::io::Write>(
     // Root container entry for the trash collection itself.
     write_trash_root_response(&mut xml, username)?;
 
+    // Pre-resolve every oc:fileid in two batch queries by object type (was one
+    // INSERT round-trip per item). File and folder UUIDs are disjoint, so the
+    // two maps merge cleanly into one keyed by original_id.
+    let mut file_uuids: Vec<String> = Vec::new();
+    let mut folder_uuids: Vec<String> = Vec::new();
+    for item in items {
+        if item.item_type == "folder" {
+            folder_uuids.push(item.original_id.clone());
+        } else {
+            file_uuids.push(item.original_id.clone());
+        }
+    }
+    let (mut id_map, folder_id_map) =
+        batch_resolve_ids(file_id_svc, &file_uuids, &folder_uuids).await;
+    id_map.extend(folder_id_map);
+
     // Individual trashed items.
     for item in items {
-        write_trash_item_response(&mut xml, item, username, file_id_svc).await?;
+        write_trash_item_response(&mut xml, item, username, file_id_svc, &id_map)?;
     }
 
     xml.write_event(Event::End(BytesEnd::new("d:multistatus")))
@@ -267,11 +284,12 @@ fn write_trash_root_response<W: std::io::Write>(
 }
 
 /// Write a single trashed item as a `<d:response>` element.
-async fn write_trash_item_response<W: std::io::Write>(
+fn write_trash_item_response<W: std::io::Write>(
     xml: &mut Writer<W>,
     item: &TrashedItemDto,
     username: &str,
     file_id_svc: Option<&Arc<NextcloudFileIdService>>,
+    id_map: &HashMap<String, i64>,
 ) -> Result<(), String> {
     xml.write_event(Event::Start(BytesStart::new("d:response")))
         .map_err(|e| e.to_string())?;
@@ -318,12 +336,8 @@ async fn write_trash_item_response<W: std::io::Write>(
     // d:getcontentlength
     write_text_element(xml, "d:getcontentlength", "0")?;
 
-    // oc:fileid and oc:id — resolve numeric ID via file_id service
-    let file_id = if item.item_type == "folder" {
-        resolve_folder_id(file_id_svc, &item.original_id).await
-    } else {
-        resolve_file_id(file_id_svc, &item.original_id).await
-    };
+    // oc:fileid and oc:id — resolved up front in a batch query.
+    let file_id = id_map.get(&item.original_id).copied();
     if let Some(id) = file_id {
         write_text_element(xml, "oc:fileid", &id.to_string())?;
         let oc_id = format_oc_id(id, file_id_svc);

src/interfaces/nextcloud/webdav_handler.rs

@@ -9,7 +9,7 @@ use quick_xml::{
     Writer,
     events::{BytesEnd, BytesStart, BytesText, Event},
 };
-use std::collections::HashSet;
+use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 
 use crate::application::adapters::webdav_adapter::{PropFindRequest, WebDavAdapter};
@@ -1001,6 +1001,26 @@ async fn write_nc_multistatus<W: std::io::Write>(
     file_id_svc: Option<&Arc<NextcloudFileIdService>>,
     favorite_ids: &HashSet<String>,
 ) -> Result<(), String> {
+    // When folder is None, files are the target resource itself (single-file
+    // PROPFIND) and must always be emitted. When folder is Some, files/subfolders
+    // are children and should only be listed when depth > 0.
+    let emit_children = folder.is_none() || depth != "0";
+
+    // Pre-resolve every oc:fileid up front in two batch queries (one per
+    // object type) instead of one INSERT round-trip per child. The XML writing
+    // below is then a pure synchronous map lookup.
+    let mut file_uuids: Vec<String> = Vec::new();
+    let mut folder_uuids: Vec<String> = Vec::new();
+    if let Some(f) = folder {
+        folder_uuids.push(f.id.clone());
+    }
+    if emit_children {
+        file_uuids.extend(files.iter().map(|f| f.id.clone()));
+        folder_uuids.extend(subfolders.iter().map(|sf| sf.id.clone()));
+    }
+    let (file_id_map, folder_id_map) =
+        batch_resolve_ids(file_id_svc, &file_uuids, &folder_uuids).await;
+
     let mut xml = Writer::new(writer);
 
     // Root element with all required namespaces.
@@ -1015,7 +1035,7 @@ async fn write_nc_multistatus<W: std::io::Write>(
     // §5.2 + strict NC-client enforcement — see `nc_collection_href`).
     if let Some(f) = folder {
         let href = nc_collection_href(username, subpath);
-        let file_id = resolve_folder_id(file_id_svc, &f.id).await;
+        let file_id = folder_id_map.get(&f.id).copied();
         let oc_id = file_id.map(|id| format_oc_id(id, file_id_svc));
         write_folder_response(
             &mut xml,
@@ -1028,11 +1048,6 @@ async fn write_nc_multistatus<W: std::io::Write>(
         )?;
     }
 
-    // When folder is None, files are the target resource itself (single-file
-    // PROPFIND) and must always be emitted. When folder is Some, files/subfolders
-    // are children and should only be listed when depth > 0.
-    let emit_children = folder.is_none() || depth != "0";
-
     if emit_children {
         // Files.
         for file in files {
@@ -1045,7 +1060,7 @@ async fn write_nc_multistatus<W: std::io::Write>(
                 format!("{}/{}", subpath.trim_end_matches('/'), file.name)
             };
             let href = nc_href(username, &child_sub);
-            let file_id = resolve_file_id(file_id_svc, &file.id).await;
+            let file_id = file_id_map.get(&file.id).copied();
             let oc_id = file_id.map(|id| format_oc_id(id, file_id_svc));
             write_file_response(
                 &mut xml,
@@ -1066,7 +1081,7 @@ async fn write_nc_multistatus<W: std::io::Write>(
                 format!("{}/{}", subpath.trim_end_matches('/'), sf.name)
             };
             let href = nc_collection_href(username, &child_sub);
-            let file_id = resolve_folder_id(file_id_svc, &sf.id).await;
+            let file_id = folder_id_map.get(&sf.id).copied();
             let oc_id = file_id.map(|id| format_oc_id(id, file_id_svc));
             write_folder_response(
                 &mut xml,
@@ -1273,20 +1288,24 @@ pub fn write_text_element<W: std::io::Write>(
     Ok(())
 }
 
-pub async fn resolve_file_id(
+/// Resolve every `oc:fileid` for a listing in two batch queries (one per
+/// object type) instead of one INSERT round-trip per child. Returns
+/// `(file_map, folder_map)` keyed by object UUID; entries are absent when the
+/// service is disabled or an id can't be resolved, mirroring the previous
+/// per-call `Option` behaviour. The two batches run concurrently.
+pub async fn batch_resolve_ids(
     svc: Option<&Arc<NextcloudFileIdService>>,
-    file_uuid: &str,
-) -> Option<i64> {
-    let svc = svc?;
-    svc.get_or_create_file_id(file_uuid).await.ok()
-}
-
-pub async fn resolve_folder_id(
-    svc: Option<&Arc<NextcloudFileIdService>>,
-    folder_uuid: &str,
-) -> Option<i64> {
-    let svc = svc?;
-    svc.get_or_create_folder_id(folder_uuid).await.ok()
+    file_uuids: &[String],
+    folder_uuids: &[String],
+) -> (HashMap<String, i64>, HashMap<String, i64>) {
+    let Some(svc) = svc else {
+        return (HashMap::new(), HashMap::new());
+    };
+    let (files, folders) = tokio::join!(
+        svc.get_or_create_file_ids(file_uuids),
+        svc.get_or_create_folder_ids(folder_uuids),
+    );
+    (files.unwrap_or_default(), folders.unwrap_or_default())
 }
 
 pub fn format_oc_id(id: i64, svc: Option<&Arc<NextcloudFileIdService>>) -> String {