Client-Side Data Storage by Raymond Camden

Author:Raymond Camden
Language: eng
Format: epub
Publisher: O'Reilly Media, Inc.
Published: 2016-01-10T16:00:00+00:00

Working with Ranges and Indexes

The cursor example you saw previously is useful for printing all the data, but typically you will want to work only with a subset of your data. This is where indexes come in. Indexes are based on a property of your data. Within that data, you can request a range of data.

So imagine an object store of people with an index on name. You could request a range of data based on names that begin with B and upward. (C, D, and so on.) You could instead request a range that begins at the “lowest” value for a name and goes up to T. Finally, you could request a range between R and S.

And to make things even more complex, for all of the preceding examples you can switch between an inclusive and exclusive mode. What does that mean? Imagine a range between B and E. An inclusive range will include B and E itself, giving you names like Barry and Elric. An exclusive range will give you values between B and E but not including names starting with those letters. So the first result may be Corwin. (And yes, numerical ranges work too.)

Finally, you can also create a “range” of one value, so, for example, just names that begin with R (like Raymond).

Working with ranges is only slightly different than cursors. Instead of opening a cursor on an object store, you open it on an index instead. As an example:

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