diff --git a/docs/interfaces/datastore-service.txt b/docs/interfaces/datastore-service.txt
index 582243e6f..b684ad9a0 100644
--- a/docs/interfaces/datastore-service.txt
+++ b/docs/interfaces/datastore-service.txt
@@ -72,7 +72,7 @@ Interface WriteRequest {
     locked_fields: {
         <fqid>: Position;
         <fqfield>: Position;
-        <CollectionField>: Position;
+        <CollectionField>: Position | CollectionFieldLock;
     }
 }
 
@@ -104,6 +104,15 @@ Interface DeleteEvent {
     fqid: Fqid;
 }
 
+// Collection fields can not only be locked to a specific position, but also filtered
+// first, e.g. when selecting all models from a specific meeting. WARNING: the filter
+// should always contain an equals check with the meeting_id, since this will be
+// indexed. Other filters can lead to long query times.
+Interface CollectionFieldLock {
+    position: Position;
+    filter: Filter;
+}
+
 // Note: The modified fqfields include:
 // - all updated fqfields
 // - all deleted fqfields
@@ -213,16 +222,22 @@ get_all(collection: Collection, mapped_fields?: Field[], get_deleted_models?: De
  */
 get_everything(get_deleted_models?: DeletedModelsBehaviour): Map<Collection, Model[]>;
 
+interface FilterResponse {
+    position: Position;
+    data: Map<Id, Partial<Model>>;
+}
+
 /**
  * Returns all models of one collection that satisfy the filter condition.
  * Url: POST to /internal/datastore/reader/filter
  *
+ * The global max position of the datastore is returned next the the filtered data.
  * This method does not take a position and can not be used when browsing the history.
  *
  * @returns see get_many
  * @throws InvalidFormat
  */
-filter(collection: Collection, filter: Filter, mapped_fields?: Field[]): Map<Id, Partial<Model>>
+filter(collection: Collection, filter: Filter, mapped_fields?: Field[]): FilterResponse
 
 /**
  * Url: POST to /internal/datastore/reader/exists