The following is the first few sections of a chapter from Android's Architecture Components, plus headings for the remaining major sections, to give you an idea about the content of the chapter.
So far, this book has portrayed Room as being an ORM-style bridge between your code and SQLite.
Technically, that is not accurate.
Part of what we get with Room is a series of classes and interfaces in the
android.support.persistence.db package. These classes come from a separate
android.arch.persistence.room:support-db) and represent an abstraction
for SQLite-style database access. This book will refer to this as “the support
We also get implementations of that abstraction, in the form of the “framework”
android.arch.persistence.room:support-db-impl). Those classes
use the Android standard SQLite environment. Room’s artifacts pull in these
support artifacts by default, and when we use
RoomDatabase.Builder to set up
RoomDatabase, we are using those “framework” classes for the database access.
In this chapter, we will explore in greater detail why this support database API exists and how we can use it, because while most of the time we will be able to use Room-generated code to work with the database, sometimes we cannot.
To many developers, SQLite “is what it is”. Android ships with a SQLite implementation, and we use it, either directly or via some form of wrapper library.
However, in truth, there are many SQLite implementations. After all, SQLite is a library, and so there is nothing stopping people from using a separate, independent copy of SQLite from what is in Android. Even in Android itself, what SQLite you get depends on what device you run on:
And so, sometimes, we need a facade: an API that we can code to that supports a pluggable implementation. The following sections outline some examples.
One of the best-known alternative SQLite implementations for Android is Zetitec’s SQLCipher for Android, which offers transparent encryption of database contents. However, Room knows nothing about SQLCipher for Android… which is why the author of this book wrote CWAC-SafeRoom, described in another chapter. The bulk of CWAC-SafeRoom is an implementation of the support database API that completely replaces the use of the framework SQLite with SQLCipher for Android.
Sometimes, you may want to package a database with the app, either as starter
data or as a read-only data source. Jeff Gilfelt’s
handle this for you, but Room does not know about it.
General/AssetRoom sample app profiled in another chapter
contains a partial implementation of the support database API. Mostly, it is
a pass-through to the stock implementation of that API that uses the framework’s
copy of SQLite. However, it uses a modified version of
handle the timely unpacking of a database stored in
Both of those use cases offer other implementations of the support database API. The idea is that not only can Room use that API, but so could other similar object-relational mapping (ORM) libraries. If those libraries write to the support database API and allow pluggable implementations the way that Room does, then solutions like CWAC-SafeRoom can work for those libraries in the same way that it works for Room itself.
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