diff --git a/src/rime/dict/db.h b/src/rime/dict/db.h
index 111eac923..1cade68f5 100644
--- a/src/rime/dict/db.h
+++ b/src/rime/dict/db.h
@@ -93,7 +93,7 @@ class Recoverable {
 
 class ResourceResolver;
 
-class DbComponentBase : virtual public ComponentBase {
+class DbComponentBase {
  public:
   DbComponentBase();
   virtual ~DbComponentBase();
@@ -108,7 +108,7 @@ template <class DbClass>
 class DbComponent : public DbClass::Component,
                     protected DbComponentBase {
  public:
-  virtual string extension() const { return string(); }
+  virtual string extension() const;
 
   DbClass* Create(const string& name) override {
     return new DbClass(DbFilePath(name, extension()), name);
diff --git a/src/rime/dict/level_db.cc b/src/rime/dict/level_db.cc
index 1ab591f99..859605e57 100644
--- a/src/rime/dict/level_db.cc
+++ b/src/rime/dict/level_db.cc
@@ -349,11 +349,6 @@ string UserDbComponent<LevelDb>::extension() const {
   return ".userdb";
 }
 
-template <>
-string UserDbComponent<LevelDb>::snapshot_extension() const {
-  return ".userdb.txt";
-}
-
 template <>
 UserDbWrapper<LevelDb>::UserDbWrapper(const string& file_name,
                                       const string& db_name)
diff --git a/src/rime/dict/table_db.cc b/src/rime/dict/table_db.cc
index 7366e16fc..611a55161 100644
--- a/src/rime/dict/table_db.cc
+++ b/src/rime/dict/table_db.cc
@@ -69,8 +69,6 @@ TableDb::TableDb(const string& file_name, const string& db_name)
     : TextDb(file_name, db_name, "tabledb", TableDb::format) {
 }
 
-// StableDb
-
 StableDb::StableDb(const string& file_name, const string& db_name)
     : TableDb(file_name, db_name) {}
 
@@ -83,4 +81,14 @@ bool StableDb::Open() {
   return TableDb::OpenReadOnly();
 }
 
+template <>
+string DbComponent<TableDb>::extension() const {
+  return ".txt";
+}
+
+template <>
+string DbComponent<StableDb>::extension() const {
+  return ".txt";
+}
+
 }  // namespace rime
diff --git a/src/rime/dict/user_db.cc b/src/rime/dict/user_db.cc
index d10495042..c35efac33 100644
--- a/src/rime/dict/user_db.cc
+++ b/src/rime/dict/user_db.cc
@@ -60,8 +60,7 @@ string UserDbComponent<TextDb>::extension() const {
   return plain_userdb_extension;
 }
 
-template <>
-string UserDbComponent<TextDb>::snapshot_extension() const {
+string UserDb::snapshot_extension() {
   return plain_userdb_extension;
 }
 
diff --git a/src/rime/dict/user_db.h b/src/rime/dict/user_db.h
index 4aa7398b7..8823cea0b 100644
--- a/src/rime/dict/user_db.h
+++ b/src/rime/dict/user_db.h
@@ -38,19 +38,21 @@ struct UserDbValue {
  */
 class UserDb {
  public:
+  static string snapshot_extension();
+
   /// Abstract class for a user db component.
   class Component : public Db::Component {
    public:
     virtual string extension() const = 0;
-    virtual string snapshot_extension() const = 0;
   };
 
   /// Requires a registered component for a user db class.
   static Component* Require(const string& name) {
-    return static_cast<Component*>(Db::Require(name));
+    return dynamic_cast<Component*>(Db::Require(name));
   }
 
   UserDb() = delete;
+
 };
 
 /// A helper class to provide extra functionalities related to user db.
@@ -102,16 +104,14 @@ class UserDbWrapper : public BaseDb {
 /// Implements a component that serves as a factory for a user db class.
 template <class BaseDb>
 class UserDbComponent : public UserDb::Component,
-                        protected DbComponent<UserDbWrapper<BaseDb>> {
+                        protected DbComponentBase {
  public:
   using UserDbImpl = UserDbWrapper<BaseDb>;
-
-  UserDbImpl* Create(const string& name) override {
-    return DbComponent<UserDbImpl>::Create(name);
+  Db* Create(const string& name) override {
+    return new UserDbImpl(DbFilePath(name, extension()), name);
   }
 
   string extension() const override;
-  string snapshot_extension() const override;
 };
 
 class UserDbMerger : public Sink {
diff --git a/src/rime/dict/user_db_recovery_task.cc b/src/rime/dict/user_db_recovery_task.cc
index 83699b7ca..b50ae8afa 100644
--- a/src/rime/dict/user_db_recovery_task.cc
+++ b/src/rime/dict/user_db_recovery_task.cc
@@ -67,8 +67,7 @@ void UserDbRecoveryTask::RestoreUserDataFromSnapshot(Deployer* deployer) {
   // locate snapshot file
   boost::filesystem::path dir(deployer->user_data_sync_dir());
   // try *.userdb.txt
-  fs::path snapshot_path =
-      dir / (dict_name + component->snapshot_extension());
+  fs::path snapshot_path = dir / (dict_name + UserDb::snapshot_extension());
   if (!fs::exists(snapshot_path)) {
     // try *.userdb.*.snapshot
     string legacy_snapshot_file =
diff --git a/src/rime/lever/user_dict_manager.cc b/src/rime/lever/user_dict_manager.cc
index 2a23f049d..c5258266e 100644
--- a/src/rime/lever/user_dict_manager.cc
+++ b/src/rime/lever/user_dict_manager.cc
@@ -67,7 +67,7 @@ bool UserDictManager::Backup(const string& dict_name) {
       return false;
     }
   }
-  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
+  string snapshot_file = dict_name + UserDb::snapshot_extension();
   return db->Backup((dir / snapshot_file).string());
 }
 
@@ -177,7 +177,7 @@ bool UserDictManager::UpgradeUserDict(const string& dict_name) {
       return false;
     }
   }
-  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
+  string snapshot_file = dict_name + UserDb::snapshot_extension();
   fs::path snapshot_path = trash / snapshot_file;
   return legacy_db->Backup(snapshot_path.string()) &&
          legacy_db->Close() &&
@@ -197,7 +197,7 @@ bool UserDictManager::Synchronize(const string& dict_name) {
     }
   }
   // *.userdb.txt
-  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
+  string snapshot_file = dict_name + UserDb::snapshot_extension();
   for (fs::directory_iterator it(sync_dir), end; it != end; ++it) {
     if (!fs::is_directory(it->path()))
       continue;