diff --git a/src/DAO/IDiariesDAO.h b/src/DAO/IDiariesDAO.h
index 3b7db99..fb416e4 100644
--- a/src/DAO/IDiariesDAO.h
+++ b/src/DAO/IDiariesDAO.h
@@ -10,22 +10,22 @@ namespace uad
 class IDiariesDAO
 {
 public:
-  virtual std::vector<diary_dto> GetDiariesByUserUUID(const std::string& login) = 0;
+  virtual std::vector<diary_dto> GetDiariesByUserUUID(std::string_view login) = 0;
 
   virtual void СreateDiary(
-    const std::string& user_uuid,
+    std::string_view user_uuid,
     const diary_dto& dto
   ) const = 0;
 
   virtual void UpdateDiary(
-    const std::string& user_uuid,
-    const std::string& diary_uuid,
+    std::string_view user_uuid,
+    std::string_view diary_uuid,
     const diary_dto& dto
   ) const = 0;
 
   virtual void DeleteDiary(
-    const std::string& user_uuid,
-    const std::string& diary_uuid
+    std::string_view user_uuid,
+    std::string_view diary_uuid
   ) const = 0;
 
   virtual ~IDiariesDAO() = default;
diff --git a/src/DAO/IUserDAO.h b/src/DAO/IUserDAO.h
index a49881b..4ac96f4 100644
--- a/src/DAO/IUserDAO.h
+++ b/src/DAO/IUserDAO.h
@@ -13,15 +13,15 @@ class IUserDAO
 public:
   virtual std::string Create(const user_dto& created_user) = 0;
 
-  virtual std::optional<user_dto> GetByUUID(const std::string& uuid) = 0;
+  virtual std::optional<user_dto> GetByUUID(std::string_view uuid) = 0;
 
-  virtual std::optional<user_dto> GetByLogin(const std::string& login) = 0;
+  virtual std::optional<user_dto> GetByLogin(std::string_view login) = 0;
 
   virtual std::pair<bool, std::vector<user_dto>> GetAll(size_t limit, size_t offset) = 0;
 
   virtual bool Update(const user_dto& u) = 0;
 
-  virtual bool Delete(const std::string& uuid) = 0;
+  virtual bool Delete(std::string_view uuid) = 0;
 
   virtual ~IUserDAO() = default;
 };
diff --git a/src/DAO/IUserTreatmentSchemesDAO.h b/src/DAO/IUserTreatmentSchemesDAO.h
index a9664c0..36a332b 100644
--- a/src/DAO/IUserTreatmentSchemesDAO.h
+++ b/src/DAO/IUserTreatmentSchemesDAO.h
@@ -8,10 +8,10 @@ namespace uad
 {
 class IUserTreatmentSchemeDAO {
 public:
-  virtual std::vector<user_treatment_scheme_dto> FindByUserUUID(const std::string& login) = 0;
+  virtual std::vector<user_treatment_scheme_dto> FindByUserUUID(std::string_view login) = 0;
 
   virtual void CreateUserTreatmentScheme(
-        const std::string& user_login,
+        std::string_view user_login,
         const user_treatment_scheme_dto& dto
     ) = 0;
 
diff --git a/src/DAO/MySQLDiariesDAO.cpp b/src/DAO/MySQLDiariesDAO.cpp
index 30efd2d..658daf3 100644
--- a/src/DAO/MySQLDiariesDAO.cpp
+++ b/src/DAO/MySQLDiariesDAO.cpp
@@ -8,7 +8,7 @@ MySqlDiariesDAO::MySqlDiariesDAO(mysqlx::Session& session) : session_(session)
 {
 }
 
-std::vector<diary_dto> MySqlDiariesDAO::GetDiariesByUserUUID(const std::string& user_uuid)
+std::vector<diary_dto> MySqlDiariesDAO::GetDiariesByUserUUID(std::string_view user_uuid)
 {
   static const std::string query = R"(
           SELECT
@@ -30,7 +30,7 @@ std::vector<diary_dto> MySqlDiariesDAO::GetDiariesByUserUUID(const std::string&
 
   mysqlx::SqlResult result = session_
                              .sql(query)
-                             .bind(user_uuid)
+                             .bind(user_uuid.data())
                              .execute();
 
   std::vector<diary_dto> diaries;
@@ -60,7 +60,7 @@ std::vector<diary_dto> MySqlDiariesDAO::GetDiariesByUserUUID(const std::string&
   return diaries;
 }
 
-void MySqlDiariesDAO::СreateDiary(const std::string& user_uuid, const diary_dto& dto) const
+void MySqlDiariesDAO::СreateDiary(std::string_view user_uuid, const diary_dto& dto) const
 {
   auto stmt = session_.sql(R"(
         INSERT INTO `up_and_down`.`diaries` (
@@ -94,7 +94,7 @@ void MySqlDiariesDAO::СreateDiary(const std::string& user_uuid, const diary_dto
 
   stmt.bind(
       dto.uuid,
-      user_uuid,
+      user_uuid.data(),
       dto.time_ms,
       dto.mania_level,
       dto.depression_level,
@@ -111,8 +111,8 @@ void MySqlDiariesDAO::СreateDiary(const std::string& user_uuid, const diary_dto
 }
 
 void MySqlDiariesDAO::UpdateDiary(
-  const std::string& user_uuid,
-  const std::string& diary_uuid,
+  std::string_view user_uuid,
+  std::string_view diary_uuid,
   const diary_dto& dto) const
 {
   auto stmt = session_.sql(R"(
@@ -140,7 +140,7 @@ void MySqlDiariesDAO::UpdateDiary(
       dto.anxiety_level,
       dto.comment,
       dto.user_treatment_scheme_uuid,
-      dto.uuid
+      diary_uuid.data()
   );
 
   auto res = stmt.execute();
@@ -151,15 +151,15 @@ void MySqlDiariesDAO::UpdateDiary(
 }
 
 void MySqlDiariesDAO::DeleteDiary(
-  const std::string& user_uuid,
-  const std::string& diary_uuid) const
+  std::string_view user_uuid,
+  std::string_view diary_uuid) const
 {
   auto stmt = session_.sql(R"(
         DELETE FROM `up_and_down`.`diaries`
         WHERE uuid = ? AND user_uuid = ?
     )");
 
-  stmt.bind(diary_uuid, user_uuid);
+  stmt.bind(diary_uuid.data(), user_uuid.data());
 
   auto res = stmt.execute();
 
diff --git a/src/DAO/MySQLDiariesDAO.h b/src/DAO/MySQLDiariesDAO.h
index dda3f91..4926927 100644
--- a/src/DAO/MySQLDiariesDAO.h
+++ b/src/DAO/MySQLDiariesDAO.h
@@ -15,22 +15,22 @@ class MySqlDiariesDAO final : public IDiariesDAO
 public:
   explicit MySqlDiariesDAO(mysqlx::Session& session);
 
-  std::vector<diary_dto> GetDiariesByUserUUID(const std::string& user_uuid) override;
+  std::vector<diary_dto> GetDiariesByUserUUID(std::string_view user_uuid) override;
 
   void СreateDiary(
-    const std::string& user_uuid,
+    std::string_view user_uuid,
     const diary_dto& dto
   ) const override;
 
   void UpdateDiary(
-    const std::string& user_uuid,
-    const std::string& diary_uuid,
+    std::string_view user_uuid,
+    std::string_view diary_uuid,
     const diary_dto& dto
   ) const override;
 
   void DeleteDiary(
-    const std::string& user_uuid,
-    const std::string& diary_uuid
+    std::string_view user_uuid,
+    std::string_view diary_uuid
   ) const override;
 };
 }
diff --git a/src/DAO/MySQLUserDAO.cpp b/src/DAO/MySQLUserDAO.cpp
index 0736382..4887c3e 100644
--- a/src/DAO/MySQLUserDAO.cpp
+++ b/src/DAO/MySQLUserDAO.cpp
@@ -31,23 +31,23 @@ string MySQLUserDAO::Create(const user_dto& created_user)
   return uuid_str;
 }
 
-optional<user_dto> MySQLUserDAO::GetByUUID(const string& uuid)
+optional<user_dto> MySQLUserDAO::GetByUUID(std::string_view uuid)
 {
   static const string sql_script = "SELECT * FROM `up_and_down`.`users` WHERE (uuid = ?) LIMIT 1;"s;
   mysqlx::SqlResult sql_result = session_.
                                  sql(sql_script)
-                                 .bind(uuid)
+                                 .bind(uuid.data())
                                  .execute();
 
   return GetSingleUserBySQLResult(std::move(sql_result));
 }
 
-optional<user_dto> MySQLUserDAO::GetByLogin(const string& login)
+optional<user_dto> MySQLUserDAO::GetByLogin(std::string_view login)
 {
   static const std::string sql_script = "SELECT * FROM `up_and_down`.`users` WHERE (login = ?) LIMIT 1;"s;
-  mysqlx::SqlResult sql_result = session_.
-                                 sql(sql_script)
-                                 .bind(login)
+  mysqlx::SqlResult sql_result = session_
+                                 .sql(sql_script)
+                                 .bind(login.data())
                                  .execute();
 
   return GetSingleUserBySQLResult(std::move(sql_result));
@@ -107,12 +107,12 @@ bool MySQLUserDAO::Update(const user_dto& u)
   return !!schema.getAffectedItemsCount();
 }
 
-bool MySQLUserDAO::Delete(const string& uuid)
+bool MySQLUserDAO::Delete(std::string_view uuid)
 {
   static const string sql_script = "DELETE FROM `up_and_down`.`users` WHERE `uuid` = ?;";
 
   auto schema = session_.sql(sql_script)
-                        .bind(uuid)
+                        .bind(uuid.data())
                         .execute();
 
   return !!schema.getAffectedItemsCount();
diff --git a/src/DAO/MySQLUserDAO.h b/src/DAO/MySQLUserDAO.h
index 4e5864a..165f704 100644
--- a/src/DAO/MySQLUserDAO.h
+++ b/src/DAO/MySQLUserDAO.h
@@ -13,15 +13,15 @@ public:
 
   std::string Create(const user_dto& created_user) override;
 
-  std::optional<user_dto> GetByUUID(const std::string& uuid) override;
+  std::optional<user_dto> GetByUUID(std::string_view uuid) override;
 
-  std::optional<user_dto> GetByLogin(const std::string& login) override;
+  std::optional<user_dto> GetByLogin(std::string_view login) override;
 
   std::pair<bool, std::vector<user_dto>> GetAll(size_t limit, size_t offset) override;
 
   bool Update(const user_dto& u) override;
 
-  bool Delete(const std::string& uuid) override;
+  bool Delete(std::string_view uuid) override;
 
 private:
   std::optional<user_dto> GetSingleUserBySQLResult(mysqlx::SqlResult&& sql_result);
diff --git a/src/DAO/MySQLUserTreatmentSchemesDAO.cpp b/src/DAO/MySQLUserTreatmentSchemesDAO.cpp
index b6fa68e..6d68db0 100644
--- a/src/DAO/MySQLUserTreatmentSchemesDAO.cpp
+++ b/src/DAO/MySQLUserTreatmentSchemesDAO.cpp
@@ -11,7 +11,7 @@ MySQLUserTreatmentSchemesDAO::MySQLUserTreatmentSchemesDAO(mysqlx::Session& sess
 }
 
 std::vector<user_treatment_scheme_dto> MySQLUserTreatmentSchemesDAO::FindByUserUUID(
-  const std::string& user_uuid)
+  std::string_view user_uuid)
 {
   static const std::string query = R"(
             SELECT
@@ -30,7 +30,7 @@ std::vector<user_treatment_scheme_dto> MySQLUserTreatmentSchemesDAO::FindByUserU
 
   mysqlx::SqlResult result = session_
                              .sql(query)
-                             .bind(user_uuid)
+                             .bind(user_uuid.data())
                              .execute();
 
   std::unordered_map<std::string, user_treatment_scheme_dto> scheme_map;
@@ -69,7 +69,7 @@ std::vector<user_treatment_scheme_dto> MySQLUserTreatmentSchemesDAO::FindByUserU
 }
 
 void MySQLUserTreatmentSchemesDAO::CreateUserTreatmentScheme(
-  const std::string& user_uuid,
+  std::string_view user_uuid,
   const user_treatment_scheme_dto& dto)
 {
   session_.startTransaction();
@@ -85,7 +85,7 @@ void MySQLUserTreatmentSchemesDAO::CreateUserTreatmentScheme(
             )")
     .bind(
         dto.uuid,
-        user_uuid,
+        user_uuid.data(),
         dto.treatment_name,
         dto.instructions
     )
diff --git a/src/DAO/MySQLUserTreatmentSchemesDAO.h b/src/DAO/MySQLUserTreatmentSchemesDAO.h
index a8802f1..e743af7 100644
--- a/src/DAO/MySQLUserTreatmentSchemesDAO.h
+++ b/src/DAO/MySQLUserTreatmentSchemesDAO.h
@@ -11,10 +11,10 @@ class MySQLUserTreatmentSchemesDAO : public IUserTreatmentSchemeDAO
 public:
   explicit MySQLUserTreatmentSchemesDAO(mysqlx::Session& session);
 
-  std::vector<user_treatment_scheme_dto> FindByUserUUID(const std::string& uuid) override;
+  std::vector<user_treatment_scheme_dto> FindByUserUUID(std::string_view uuid) override;
 
   void CreateUserTreatmentScheme(
-        const std::string& user_login,
+        std::string_view user_login,
         const user_treatment_scheme_dto& dto
     ) override;
 };
diff --git a/src/helpers/helpers.cpp b/src/helpers/helpers.cpp
index dee82aa..07a5ce9 100644
--- a/src/helpers/helpers.cpp
+++ b/src/helpers/helpers.cpp
@@ -117,9 +117,9 @@ std::string ToHex(std::byte* src, size_t len)
   return ret;
 }
 
-std::string HashPassword(const std::string& password)
+std::string HashPassword(std::string_view password)
 {
-  size_t calculated_hash = std::hash<string>{}(password);
+  size_t calculated_hash = std::hash<std::string_view>{}(password);
   return ToHex((byte*)&calculated_hash, sizeof(calculated_hash));
 }
 
diff --git a/src/helpers/helpers.h b/src/helpers/helpers.h
index e1def2f..625c549 100644
--- a/src/helpers/helpers.h
+++ b/src/helpers/helpers.h
@@ -12,7 +12,7 @@ void Fail(boost::beast::error_code ec, char const* what);
 
 std::string ToHex(std::byte* src, size_t len);
 
-std::string HashPassword(const std::string& password);
+std::string HashPassword(std::string_view password);
 
 std::string GenerateUUID();