Android - Parameter to execute dynamic query

I have a query in my main application, that shows all the registers of my database.

I have a button in my application that gets into another activity. There, i can filter my query ( for example, i have a book table and i just want books from an author and with an specific price)

So with a spinner i select my options and with an intent and put extra i pass the variables to my principal activity, so i can show the query filtered.

Here is the example

String selGrado =  this.getIntent().getExtras().getString("grado");


 String query = "Select * FROM Incidentes WHERE 1=1";

   if () query+= " AND codGr='"+selGrado+"'";



     Cursor d = db2.rawQuery(query,null);

So, i want my query to execute with the parameter selGrado that i filled in my "filter" activity. Which condition should i put? Because when application starts, i want to show all registers so its no problem avoiding the filter, and i want to execute just Select * from Incidentes .. 开发者_开发问答and if i query trough FILTER activity, i want the query knows about which option i selected. is there any way to ask if the getExtra i receive is null or something like that? thanks

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Yes you can check extras by using the intent method hasExtra:

this.getIntent().hasExtra("grado");

but you could also check to see if selGrado is null

if(selGrado!=null)

a better way to do this is with the regular query instead of rawquery

String selection = null;
String[] selectionArgs = null;

if(getIntent().hasExtra("grado")) 
{
    selection = "codGr=?";
    selectionArgs = new String[]{getIntent().getStringExtra("grado")};
}

Cursor c = db2.query("Incidentes",null,selection, selectionargs, null);