enh(MongoDB): Add read-preference validation to replica set connection and pool.

MongoDB/include/Poco/MongoDB/ReplicaSetConnection.h

@@ -100,6 +100,12 @@ public:
 	[[nodiscard]] bool isConnected() const;
 		/// Returns true if currently connected to a server.
 
+	[[nodiscard]] bool matchesReadPreference() const;
+		/// Returns true if the currently connected server still matches the read preference.
+		/// Returns false if not connected or if the server no longer satisfies the read preference.
+		/// This is useful for connection pool validation to detect when a server role has changed
+		/// (e.g., primary became secondary).
+
 private:
 	void ensureConnection();
 		/// Ensures we have an active connection, creating one if needed.

MongoDB/include/Poco/MongoDB/ReplicaSetPoolableConnectionFactory.h

@@ -62,8 +62,10 @@ public:
 
 	bool validateObject(MongoDB::ReplicaSetConnection::Ptr pObject)
 	{
-		// Check if the connection is still valid
-		return pObject->isConnected();
+		// Check if the connection is still valid and matches the read preference.
+		// This ensures that if a server changes role (e.g., primary becomes secondary),
+		// the cached connection is invalidated and a new one is created.
+		return pObject->isConnected() && pObject->matchesReadPreference();
 	}
 
 	void activateObject(MongoDB::ReplicaSetConnection::Ptr pObject)

MongoDB/src/ReplicaSetConnection.cpp

@@ -116,6 +116,42 @@ bool ReplicaSetConnection::isConnected() const
 }
 
 
+bool ReplicaSetConnection::matchesReadPreference() const
+{
+	if (!isConnected())
+	{
+		return false;
+	}
+
+	// Get the current topology
+	TopologyDescription topology = _replicaSet.topology();
+
+	// Get the server description for the currently connected server
+	ServerDescription server = topology.getServer(_connection->address());
+
+	// Check if the server is Unknown or has an error
+	if (server.type() == ServerDescription::Unknown || server.hasError())
+	{
+		return false;
+	}
+
+	// Use ReadPreference::selectServers to check if our current server
+	// would be selected with the current read preference
+	std::vector<ServerDescription> eligibleServers = _readPreference.selectServers(topology);
+
+	// Check if our current server is in the list of eligible servers
+	for (const auto& eligible : eligibleServers)
+	{
+		if (eligible.address() == _connection->address())
+		{
+			return true;
+		}
+	}
+
+	return false;
+}
+
+
 void ReplicaSetConnection::ensureConnection()
 {
 	if (_connection.isNull())