rx java - Sequential Observable Web Service and Database Query Call -

how implement sequential web service , database query call using rxjava observable? first call database query (cache) display result (onnext or oncompleted) , after network call display (replace) current result (cache). i'm using volley listener display data.

sequential actions can implemented using concat. because 2 concatenated observables can of different types ignoreelements , cast can useful:

databasequeryobservable     .doonnext(displayresult)     .dooncomplete(something)     .ignoreelements()     .cast(object.class)     .concatwith(         networkcall             .doonnext(displaynetworkcallresult)             .dooncomplete(somethingelse)             .ignoreelements()             .cast(object.class)     ).subscribe(onnextaction, onerroraction, oncompletedaction);