Will an empty SQLite cursor return true for isBeforeFirst, isAfterLast, both or not?

Question

This is a pretty simple question. I hope the answer is “both,” but I don't bother either. I carefully studied the Android developer docs for SQLiteDatabase and Cursor , but cannot find a definitive answer to this question.

The case I'm asking is where I get the cursor, call moveToFirst , and then loop until isAfterLast returns true. It would be very convenient for a template that I code several times if it just worked and executed a loop 0 times if the cursor has 0 records.

Or do I need to explicitly check for an empty cursor?

EDIT: Some of the answers show that people do not quite get what I ask. Basically, I would like to write the following:

 cursor = myDb.query(...) cursor.moveToFirst() while (!cursor.isAfterLast()) { processRow(...) } 

But I'm not 100% sure that I can. isAfterLast cannot return anything useful, but true for this case, but that does not mean that it really returns true for an empty request. The docs don't seem to indicate what the return value of most cursor methods is if the cursor is empty (in fact, Android docs look nonspecific in many cases with corners) other than getCount . So I'm worried that I need to do this:

 cursor = myDb.query(...) if (cusror.getCount() > 0) { cursor.moveToFirst() while (!cursor.isAfterLast()) { processRow(...) } } 

This is random and logically redundant. Keep in mind that in a real implementation there is more code and this extends to several methods. And one of the answers now suggests that I need to also check the cursor for null , which is completely undocumented ...

I just want to know if anyone knows about the actual behavior of isAfterLast when calling an empty cursor.

Answer 1

I do not use isAfterLast . I use the following template to read the result of a query.

  SQLiteDatabase db = new DbHelper().getWritableDatabase(); String sql = "SELECT ..."; String[] args = ...; Cursor cs = db.rawQuery(sql, args); while (cs.moveToNext()) { // cs.getXxx(0), cs.getXxx(1) } cs.close(); db.close(); 

DbHelper is the class that I continue from SQLiteOpenHelper

Answer 2

When the cursor is empty

cursor.moveToFirst () returns false
cursor.isBeforeFirst () returns true
cursor.isAfterLast () returns true

So yes, the first piece of code you posted will work just fine on an empty cursor.