Ruby/chef: IF ELSE statement

Trying to set template variable {USE_EXISTING_SCHEMA} to = true or false based on whether or not {CREATE_OID_SCHEMA} is = to true. should I be using == or = when specifying the IF condition of {CREATE_OID_SCHEMA}?

case node['fmw']['shortname']
      when /oid1/
        IS_SECOND_OID_INSTALL = "false"
        CONFIGURE_OVD_COMPONENT = "true"
        CREATE_OID_SCHEMA = "true"
          if CREATE_OID_SCHEMA = "true" then
            USE_EXISTING_SCHEMA = "false"
          else USE_EXISTING_SCHEMA = "true"
      when /oid2/
        IS_SECOND_OID_INSTALL = "true"
        CONFIGURE_OVD_COMPONENT = "false"
        CREATE_OID_SCHEMA = "false"
          if CREATE_OID_SCHEMA = "true" then
            USE_EXISTING_SCHEMA = "false"
          else USE_EXISTING_SCHEMA = "true"
    end