Allowing empty result sets

Author: mariano

lib/node-db

@@ -83,10 +83,5 @@ node_db::Result* node_db_mysql::Connection::query(const std::string& query) cons
         throw node_db::Exception(mysql_error(this->connection));
     }
 
-    MYSQL_RES* result = mysql_store_result(this->connection);
-    if (result == NULL) {
-        throw node_db::Exception("Could not fetch result of query");
-    }
-
-    return new node_db_mysql::Result(this->connection, result);
+    return new node_db_mysql::Result(this->connection);
 }

src/connection.cc

@@ -67,36 +67,40 @@ node_db::Result::Column::type_t node_db_mysql::Result::Column::getType() const {
     return this->type;
 }
 
-node_db_mysql::Result::Result(MYSQL* connection, MYSQL_RES* result) throw(node_db::Exception&)
+node_db_mysql::Result::Result(MYSQL* connection) throw(node_db::Exception&)
     : columns(NULL),
     totalColumns(0),
     rowNumber(0),
+    empty(true),
     connection(connection),
-    result(result),
     previousRow(NULL),
     nextRow(NULL) {
-    if (this->result == NULL) {
-        throw node_db::Exception("Invalid result");
-    }
 
-    MYSQL_FIELD* fields = mysql_fetch_fields(this->result);
-    if (fields == NULL) {
-        throw node_db::Exception("Could not buffer columns");
-    }
+    this->result = mysql_store_result(this->connection);
+    if (result == NULL && mysql_field_count(this->connection) != 0) {
+        throw node_db::Exception(mysql_error(this->connection));
+    } else if (result != NULL) {
+        this->empty = false;
 
-    this->totalColumns = mysql_num_fields(this->result);
-    if (this->totalColumns > 0) {
-        this->columns = new Column*[this->totalColumns];
-        if (this->columns == NULL) {
-            throw node_db::Exception("Could not allocate storage for columns");
+        MYSQL_FIELD* fields = mysql_fetch_fields(this->result);
+        if (fields == NULL) {
+            throw node_db::Exception("Could not buffer columns");
         }
 
-        for (uint16_t i = 0; i < this->totalColumns; i++) {
-            this->columns[i] = new Column(fields[i]);
+        this->totalColumns = mysql_num_fields(this->result);
+        if (this->totalColumns > 0) {
+            this->columns = new Column*[this->totalColumns];
+            if (this->columns == NULL) {
+                throw node_db::Exception("Could not allocate storage for columns");
+            }
+
+            for (uint16_t i = 0; i < this->totalColumns; i++) {
+                this->columns[i] = new Column(fields[i]);
+            }
         }
-    }
 
-    this->nextRow = this->row();
+        this->nextRow = this->row();
+    }
 }
 
 node_db_mysql::Result::~Result() {
@@ -175,3 +179,7 @@ uint64_t node_db_mysql::Result::count() const throw(node_db::Exception&) {
 bool node_db_mysql::Result::isBuffered() const throw() {
     return (!this->result->handle || this->result->handle->status != MYSQL_STATUS_USE_RESULT);
 }
+
+bool node_db_mysql::Result::isEmpty() const throw() {
+    return this->empty;
+}

src/result.cc

@@ -25,7 +25,7 @@ class Result : public node_db::Result {
                 bool binary;
         };
 
-        explicit Result(MYSQL* connection, MYSQL_RES* result) throw(node_db::Exception&);
+        explicit Result(MYSQL* connection) throw(node_db::Exception&);
         ~Result();
         bool hasNext() const;
         char** next() throw(node_db::Exception&);
@@ -38,11 +38,13 @@ class Result : public node_db::Result {
         uint16_t warningCount() const;
         uint64_t count() const throw(node_db::Exception&);
         bool isBuffered() const throw();
+        bool isEmpty() const throw();
 
     protected:
         Column** columns;
         uint16_t totalColumns;
         uint64_t rowNumber;
+        bool empty;
 
         char** row() throw(node_db::Exception&);