RoR Find using Conditions, or find_by_sql?

Hi, im trying to query my database and am passing a type variable with value "Hardware", a manufacturer variable with value of "Dell and an invoice variable with value of "SI11244"

Here is the url im putting into my browser:
http://localhost:3000/assets/findbyparams?manufacturer=Dell&type=Hardware&invoice=SI11244

i have a findbyparams method in my controller but have no idea how to put these values into a find statement to return the aassets where the TYPE column equals "Hardware, the MANUFACTURER column equals "Dell" and INVOICE column equals "SI11244"

thanks