If I understand well, you would like to send data from the client to a server-side database.

Lightstreamer does not focus on this task, as it can be accomplished with the help of the Web Server which always sits beside it.
Anyway, a simple transport mechanism is available through the SendMessage API, by which you can send a raw text that will be received by the Metadata Adapter in notifyUserMessage method, where you can process it properly.

Some examples included in the distribution package use this feature.
See the Portfolio Demo, the Chat Demo and the Messenger Demo.