migrations now run with savepoints

db/Schema.cpp

@@ -3,7 +3,6 @@
 
 #include "migrations/1624829187_create_events.h"
 
-
 namespace db {
   namespace db_builder = db::migrations::builder;
 
@@ -23,37 +22,64 @@ namespace db {
   void Schema::set_user_version(uint32_t version) {
     try {
       m_db->exec("PRAGMA user_version = " + std::to_string(version) + ";");
+      m_user_version = version;
     } catch (std::exception& e) {
       std::cout << "Exception: " << e.what() << std::endl;
     }
   }
 
-  void Schema::run_migrations() {
+  void Schema::set_savepoint() {
+    try {
+      m_db->exec("BEGIN;");
+      m_db->exec("SAVEPOINT " + m_migration_savepoint + ";");
+    } catch (std::exception& e) {
+      std::cout << "Exception: " << e.what() << std::endl;
+    }
+  }
+
+  void Schema::rollback_migrations() {
+    try {
+      m_db->exec("ROLLBACK TO " + m_migration_savepoint + ";");
+    } catch (std::exception& e) {
+      std::cout << "Exception: " << e.what() << std::endl;
+    }
+  }
+
+  void Schema::commit_migrations() {
+    try {
+      m_db->exec("COMMIT;");
+    } catch (std::exception& e) {
+      std::cout << "Exception: " << e.what() << std::endl;
+    }
+
+  }
+
+  uint32_t Schema::run_migrations() {
     assemble_migrations();
     if(migrations.begin() == migrations.end()) {
       DEBUG << "No migrations found...";
-      return;
+      return ERROR_NO_MIGRATIONS;
     }
-    // TODO try and catch block
-    // migration should stop on error and restore old schema
-
+    set_savepoint();
     uint32_t user_version = get_user_version();
     for(auto const& [epoch, migration] : migrations) {
       if(epoch <= user_version) {
         DEBUG << "Skipping: " << migration->get_migration_name();
         continue;
       }
-      DEBUG << "migrating: " << migration->get_migration_name();
+      std::cout << "migrating: " << migration->get_migration_name() << std::endl;
       try {
         m_db->exec(migration->get_statement());
       } catch (std::exception& e) {
         std::cout << "Exception: " << e.what() << std::endl;
+        std::cout << "Rolling back migrations..." << std::endl;
+        rollback_migrations();
+        return ERROR_FAULTY_MIGRATION;
       }
     }
-    DEBUG << migrations.rbegin()->first;
+    commit_migrations();
     set_user_version(migrations.rbegin()->first);
-    user_version = get_user_version();
-    DEBUG << user_version;
+    return 0;
   }
 
   void Schema::assemble_migrations() {

db/Schema.h

@@ -8,14 +8,19 @@ namespace db {
   class Schema {
   public:
     Schema(sql::Database* db);
-    void run_migrations();
+    uint32_t run_migrations();
 
   private:
     uint32_t get_user_version() const;
     void set_user_version(uint32_t user_version);
+    void set_savepoint();
+    void rollback_migrations();
+    void commit_migrations();
     void assemble_migrations();
 
     sql::Database* m_db;
+    uint32_t m_user_version;
+    const std::string m_migration_savepoint = "migrations_savepoint";
     std::map<uint32_t, db::migrations::Migration*> migrations;
   };
 }

db/db.h

@@ -3,6 +3,9 @@
 #include <SQLiteCpp.h>
 #include <io/debug.h>
 
+#define ERROR_NO_MIGRATIONS -2
+#define ERROR_FAULTY_MIGRATION -1
+
 namespace sql = SQLite;
 
 #include <db/Schema.h>