[TYPO3-Solr] how to filter on a specific SOLR field using a HTML-dropdown

[Michael Huber]

Hi,

I'd like to set up a SOLR search in TYPO3 with additional search params 
which should be available in a dropdown before sending the search 
request.

For example I have a custom SOLR core with adjusted schema.xml where 
each entry has a field "category" (e.g. "car" or "motorcycle", "truck") 
and a field "description" containing a long text to this vehicle. Now 
user should be able to search for a word in the field "description" and 
additionally choose a category in a dropdown-box.

Unfortunately I've now idea how to figure this in typoscript. Could you 
please give me some advice how to configure the additional param to be a 
filter on "category"?

Which name-attribute should the dropdown-input have to send the right 
url-param? I know the regular search-field is sent as "tx_solr[q]" so 
how should this be for the category?


Kind regards

Michael