6 files changed, 30 insertions, 0 deletions
diff --git a/src/mongo/db/catalog/collection.h b/src/mongo/db/catalog/collection.h
index fa2971473a3..be1d242abd9 100644
--- a/src/mongo/db/catalog/collection.h
+++ b/src/mongo/db/catalog/collection.h
@@ -586,6 +586,12 @@ public:
      */
     virtual void updateHiddenSetting(OperationContext* opCtx, StringData idxName, bool hidden) = 0;
 
+    /*
+     * Converts the the given index to be unique.
+     * This is a one-way transformation - the uniqueness constraint cannot be removed.
+     */
+    virtual void updateUniqueSetting(OperationContext* opCtx, StringData idxName) = 0;
+
     /**
      * Removes invalid index options on all indexes in this collection. Returns a list of index
      * names that contained invalid index options.
diff --git a/src/mongo/db/catalog/collection_impl.cpp b/src/mongo/db/catalog/collection_impl.cpp
index a121b6d67c2..324475d345a 100644
--- a/src/mongo/db/catalog/collection_impl.cpp
+++ b/src/mongo/db/catalog/collection_impl.cpp
@@ -1892,6 +1892,15 @@ void CollectionImpl::updateHiddenSetting(OperationContext* opCtx, StringData idx
     });
 }
 
+void CollectionImpl::updateUniqueSetting(OperationContext* opCtx, StringData idxName) {
+    int offset = _metadata->findIndexOffset(idxName);
+    invariant(offset >= 0);
+
+    _writeMetadata(opCtx, [&](BSONCollectionCatalogEntry::MetaData& md) {
+        md.indexes[offset].updateUniqueSetting();
+    });
+}
+
 std::vector<std::string> CollectionImpl::removeInvalidIndexOptions(OperationContext* opCtx) {
     std::vector<std::string> indexesWithInvalidOptions;
 
diff --git a/src/mongo/db/catalog/collection_impl.h b/src/mongo/db/catalog/collection_impl.h
index 55684e7e275..d1139a023c4 100644
--- a/src/mongo/db/catalog/collection_impl.h
+++ b/src/mongo/db/catalog/collection_impl.h
@@ -434,6 +434,8 @@ public:
 
     void updateHiddenSetting(OperationContext* opCtx, StringData idxName, bool hidden) final;
 
+    void updateUniqueSetting(OperationContext* opCtx, StringData idxName) final;
+
     std::vector<std::string> removeInvalidIndexOptions(OperationContext* opCtx) final;
 
     void setIsTemp(OperationContext* opCtx, bool isTemp) final;
diff --git a/src/mongo/db/catalog/collection_mock.h b/src/mongo/db/catalog/collection_mock.h
index 3340930e5dc..63e0515b92a 100644
--- a/src/mongo/db/catalog/collection_mock.h
+++ b/src/mongo/db/catalog/collection_mock.h
@@ -403,6 +403,10 @@ public:
         std::abort();
     }
 
+    void updateUniqueSetting(OperationContext* opCtx, StringData idxName) {
+        std::abort();
+    }
+
     std::vector<std::string> removeInvalidIndexOptions(OperationContext* opCtx) {
         std::abort();
     }
diff --git a/src/mongo/db/storage/bson_collection_catalog_entry.cpp b/src/mongo/db/storage/bson_collection_catalog_entry.cpp
index 5f474a5c82a..fca3b271332 100644
--- a/src/mongo/db/storage/bson_collection_catalog_entry.cpp
+++ b/src/mongo/db/storage/bson_collection_catalog_entry.cpp
@@ -140,6 +140,13 @@ void BSONCollectionCatalogEntry::IndexMetaData::updateHiddenSetting(bool hidden)
 }
 
 
+void BSONCollectionCatalogEntry::IndexMetaData::updateUniqueSetting() {
+    BSONObjBuilder b(spec);
+    b.appendBool("unique", true);
+    spec = b.obj();
+}
+
+
 // --------------------------
 
 int BSONCollectionCatalogEntry::MetaData::getTotalIndexCount() const {
diff --git a/src/mongo/db/storage/bson_collection_catalog_entry.h b/src/mongo/db/storage/bson_collection_catalog_entry.h
index 0d7125445ef..65f08aa3c95 100644
--- a/src/mongo/db/storage/bson_collection_catalog_entry.h
+++ b/src/mongo/db/storage/bson_collection_catalog_entry.h
@@ -97,6 +97,8 @@ public:
 
         void updateHiddenSetting(bool hidden);
 
+        void updateUniqueSetting();
+
         StringData nameStringData() const {
             return spec["name"].valueStringDataSafe();
         }