add checks to block main graph create/drop

src/include/main/database_manager.h

@@ -33,11 +33,9 @@ class DatabaseManager {
     void loadGraphsFromCatalog(storage::MemoryManager* memoryManager,
         main::ClientContext* clientContext);
     void setDefaultGraph(const std::string& graphName);
-    void clearDefaultGraph();
     bool hasGraph(const std::string& graphName);
-    catalog::Catalog* getGraphCatalog(const std::string& graphName);
     catalog::Catalog* getDefaultGraphCatalog() const;
-    bool hasDefaultGraph() const { return defaultGraph != "" && defaultGraph != "main"; }
+    bool hasDefaultGraph() const { return defaultGraph != ""; }
     std::string getDefaultGraphName() const { return defaultGraph; }
     std::vector<catalog::Catalog*> getGraphs() const;
     storage::StorageManager* getDefaultGraphStorageManager() const;

src/main/database_manager.cpp

@@ -111,6 +111,11 @@ void DatabaseManager::createGraph(const std::string& graphName,
     storage::MemoryManager* memoryManager, main::ClientContext* clientContext, bool isAnyGraph) {
     auto upperCaseName = StringUtils::getUpper(graphName);
 
+    // main is the default graph
+    if (upperCaseName == "MAIN") {
+        throw RuntimeException{"MAIN is a reserved graph name."};
+    }
+
     // Check if graph already exists in system catalog
     auto mainCatalog = clientContext->getDatabase()->getCatalog();
     auto transaction = TransactionContext::Get(*clientContext)->getActiveTransaction();
@@ -196,9 +201,6 @@ void DatabaseManager::createGraph(const std::string& graphName,
     }
 
     graphs.push_back(std::move(catalog));
-    if (defaultGraph == "") {
-        defaultGraph = graphName;
-    }
 }
 
 void DatabaseManager::dropGraph(const std::string& graphName, main::ClientContext* clientContext) {
@@ -259,10 +261,12 @@ void DatabaseManager::dropGraph(const std::string& graphName, main::ClientContex
 
 void DatabaseManager::setDefaultGraph(const std::string& graphName) {
     auto upperCaseName = StringUtils::getUpper(graphName);
+
     if (upperCaseName == "MAIN") {
-        defaultGraph = "main";
+        defaultGraph = "";
         return;
     }
+
     for (auto& graph : graphs) {
         auto graphNameUpper = StringUtils::getUpper(graph->getCatalogName());
         if (graphNameUpper == upperCaseName) {
@@ -273,10 +277,6 @@ void DatabaseManager::setDefaultGraph(const std::string& graphName) {
     throw BinderException{std::format("No graph named {}.", graphName)};
 }
 
-void DatabaseManager::clearDefaultGraph() {
-    defaultGraph = "main";
-}
-
 void DatabaseManager::loadGraphsFromCatalog(storage::MemoryManager* memoryManager,
     main::ClientContext* clientContext) {
     auto mainCatalog = clientContext->getDatabase()->getCatalog();
@@ -322,11 +322,6 @@ void DatabaseManager::loadGraphsFromCatalog(storage::MemoryManager* memoryManage
         catalog->setStorageManager(std::move(storageManager));
 
         graphs.push_back(std::move(catalog));
-
-        // Set first loaded graph as default if no default set
-        if (defaultGraph == "") {
-            defaultGraph = graphName;
-        }
     }
 }
 
@@ -341,19 +336,8 @@ bool DatabaseManager::hasGraph(const std::string& graphName) {
     return false;
 }
 
-catalog::Catalog* DatabaseManager::getGraphCatalog(const std::string& graphName) {
-    auto upperCaseName = StringUtils::getUpper(graphName);
-    for (auto& graph : graphs) {
-        auto graphNameUpper = StringUtils::getUpper(graph->getCatalogName());
-        if (graphNameUpper == upperCaseName) {
-            return graph.get();
-        }
-    }
-    throw BinderException{std::format("No graph named {}.", graphName)};
-}
-
 catalog::Catalog* DatabaseManager::getDefaultGraphCatalog() const {
-    if (defaultGraph == "" || defaultGraph == "main") {
+    if (defaultGraph == "") {
         return nullptr;
     }
     auto upperCaseName = StringUtils::getUpper(defaultGraph);

src/processor/operator/ddl/drop.cpp

@@ -124,6 +124,11 @@ void Drop::dropGraph(const main::ClientContext* context) {
     auto dbManager = main::DatabaseManager::Get(*context);
     auto memoryManager = storage::MemoryManager::Get(*context);
 
+    // Protect the main graph unconditionally — IF EXISTS cannot bypass this.
+    if (StringUtils::getUpper(dropInfo.name) == "MAIN") {
+        throw BinderException("Cannot drop the main graph.");
+    }
+
     if (!dbManager->hasGraph(dropInfo.name)) {
         auto message = std::format("Graph {} does not exist.", dropInfo.name);
         switch (dropInfo.conflictAction) {
@@ -139,11 +144,6 @@ void Drop::dropGraph(const main::ClientContext* context) {
         }
     }
 
-    if (dbManager->hasDefaultGraph() && StringUtils::getUpper(dbManager->getDefaultGraphName()) ==
-                                            StringUtils::getUpper(dropInfo.name)) {
-        dbManager->clearDefaultGraph();
-    }
-
     dbManager->dropGraph(dropInfo.name, const_cast<main::ClientContext*>(context));
     appendMessage(std::format("Graph {} has been dropped.", dropInfo.name), memoryManager);
 }

test/test_files/graph/any_graph.test

@@ -33,3 +33,20 @@ _nodes
 
 -STATEMENT DROP GRAPH mygraph
 ---- ok
+
+-CASE AnyGraphNamedMain
+
+-LOG CreateAnyGraphNamedMain
+-STATEMENT CREATE GRAPH main ANY
+---- error
+Runtime exception: MAIN is a reserved graph name.
+
+-LOG CreateAnyGraphNamedMainUpperCase
+-STATEMENT CREATE GRAPH MAIN ANY
+---- error
+Runtime exception: MAIN is a reserved graph name.
+
+-LOG CreateAnyGraphNamedMainMixedCase
+-STATEMENT CREATE GRAPH Main ANY
+---- error
+Runtime exception: MAIN is a reserved graph name.

test/test_files/graph/graph.test

@@ -125,6 +125,51 @@ person|foo1(graph)
 -STATEMENT DROP GRAPH foo1
 ---- ok
 
+-CASE MainGraphProtection
+
+-LOG CreateGraphNamedMain
+-STATEMENT CREATE GRAPH main
+---- error
+Runtime exception: MAIN is a reserved graph name.
+
+-LOG CreateGraphNamedMainUpperCase
+-STATEMENT CREATE GRAPH MAIN
+---- error
+Runtime exception: MAIN is a reserved graph name.
+
+-LOG CreateGraphNamedMainMixedCase
+-STATEMENT CREATE GRAPH Main
+---- error
+Runtime exception: MAIN is a reserved graph name.
+
+-LOG DropGraphMain
+-STATEMENT DROP GRAPH main
+---- error
+Binder exception: Cannot drop the main graph.
+
+-LOG DropGraphMainUpperCase
+-STATEMENT DROP GRAPH MAIN
+---- error
+Binder exception: Cannot drop the main graph.
+
+-LOG DropGraphMainMixedCase
+-STATEMENT DROP GRAPH Main
+---- error
+Binder exception: Cannot drop the main graph.
+
+-LOG DropGraphIfExistsMain
+-STATEMENT DROP GRAPH IF EXISTS main
+---- error
+Binder exception: Cannot drop the main graph.
+
+-LOG UseGraphMain
+-STATEMENT USE GRAPH main
+---- ok
+
+-LOG UseGraphMainUpperCase
+-STATEMENT USE GRAPH MAIN
+---- ok
+
 -CASE ErrorCases
 -LOG DuplicateGraphError
 -STATEMENT CREATE GRAPH graph1_ec