SQLite Android Bindings

<h1> 
SQLite Android Bindings 
</h1>

<p> The SQLite library is a core part of the Android environment. Java
applications and content providers access SQLite using the interface in
the 
<a href="http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html">android.database.sqlite</a> namespace.






<p> For most applications, this is convenient and works well. However,




it means that applications must be content with the SQLite version and

build installed on the target device as part of the operating system.

If your application happens to require a newer version of SQLite, or a build





with a custom extension or <a href=http://www.sqlite.org/vfs.html>VFS</a>



installed, you're out of luck. 


































<p> One solution is to bundle the SQLite library directly into the 

application, bypassing the version built-in to Android. This project,




the <i>SQLite Android bindings</i>, provides an easy way to do just



that. This allows an application to use a custom build or version of 




SQLite, regardless of the Android version to which it is deployed, while








continuing to use the standard Android interface.





















Available User Documentation:







  *  [./install.wiki | Installation Guide ] - this page describes the various



     ways the the SQLite Android bindings may be integrated with an

     application.






































  *  [./usage.wiki | Application Programming ] - this page describes the





     very minor code modifications required to use the SQLite Android bindings



     instead of Android's built-in SQLite support.










  *  [./see.wiki | Using the Simple Encryption Extension (SEE) ] - extra notes



  regarding the use of the proprietary encryption extension SEE.

<h1>Installation</h1>


<p> There are three ways to add the SQLite Android bindings to an application:

<ol>
  <li> By adding a pre-built aar file to the applications 
  <a href=https://developer.android.com/studio/index.html>Android Studio</a>
       project.

  <li> By building an aar file, then adding it to the applications Android
       Studio project as in (1).

  <li> By adding the SQLite Android bindings source code to and building it 
       along with the other application code.
</ol>

<p> By default, the SQLite Android bindings support Android API levels 16 
and greater (Android versions 4.1 and up). There is also a separate version
that supports Android API levels 15 and greater (Android version 4.0.2 and 
up). Please note the extra step involved in [#obtaincode|obtaining the code] 
if you wish to use the version compatible with API level 15.

<h2> <a name=prebuilt></a> 1. Using a Pre-Built aar File</h2>

<p>
  This is the most straightforward option. An "aar" file is similar to a 
  jar file, except that it may contain both compiled java classes and 
  native code. An aar file for the latest SQLite release usable with
  API levels 16 and up is available from 
  <a href=http://sqlite.org/download.html>this page</a>.
  
<p>
  There are two steps involved in adding an aar file to an Android Studio
  project:

<p>
  <ol>
    <li> <b>Import the module</b>. In Android Studio 2.1 this is
    accomplished by selecting the <code>"File" -> "New" -> "New
    Module..."</code> menu and then choosing <code>"Import JAR/AAR
    Package"</code>.

    <li> <b>Add a dependency on the new module to the main application</b>
    module (or to all modules that will use the SQLite Android bindings).  In
    Android Studio 2.1 the dependency may be created using the project
    structure dialog (select <code>"File" -> "Project Structure..."</code>) or
    by adding code similar to the following to the application modules
    <code>build.gradle</code> file: <verbatim>
    dependencies {
        <i>// Change "sqlite3-release" to the name of the new module!</i>
        compile project(':sqlite3-release')
    }</verbatim>
</ol>
<p>
  At time of writing, aar files may only be used directly in Android Studio
  projects, not projects created using other IDEs (e.g. Eclipse, IntelliJ
  IDEA). However, an aar is just a zip archive containing a
  <code>classes.jar</code> file that in turn contains the SQLite Android
  binding java classes and a <code>jni/</code> directory that contains the 
  native library for each platform.  By extracting these two things from the 
  aar file and adding them to the project separately it is often possible to 
  use an aar file in non-Android Studio projects.

<h2>2. <a name=customaar></a> Building a Custom aar File</h2>

<p>
  Building a custom aar file requires both the Android SDK and NDK. 

<ol>
  <li><a name=obtaincode></a><b>Obtain the code</b>. The code for the SQLite Android bindings may
  be obtained either by checking out 
  the <a href=http://fossil-scm.org>fossil</a> repository, or by downloading
  a zip file.
  <p>
  To obtain the code using fossil, use the following series of commands.
  In this case, the "project directory" refered to in subsequent steps is
  the <code>sqlite</code> directory created by the second command below:
  <p>
  <verbatim>
    $ fossil clone http://www.sqlite.org/android android.fossil
    $ mkdir sqlite
    $ cd sqlite
    $ fossil open ../android.fossil</verbatim>
  <p>
  Alternatively, the latest code may be downloaded as a 
  <a href=http://www.sqlite.org/android/zip/SQLite+Android+Bindings.zip?uuid=trunk>zip archive</a>. 
  In this case, the "project directory" is the
  <code>SQLite_Android_Bindings/</code> directory created by unzipping the
  downloaded archive.
  <p>
  <i>API level 15 users:</i> The code for the version that is
  compatible with Android API level 15 may be obtained as a zip
  file 
  <a href=http://www.sqlite.org/android/zip/SQLite+Android+Bindings.zip?uuid=api-level-15>from here</a>.
  Or, if using fossil, the <code>fossil open</code> command above should be
  replaced with: 
  <verbatim>
    $ fossil open ../android.fossil api-level-15</verbatim>

  <li><a name=buildnative></a> <b>Build the native libraries.</b>
  <p> To build the native libraries, navigate to the
      <code>sqlite3/src/main/</code> directory of the project directory and
      run the <code>ndk-build</code> command. For example, on Linux if 
      Android Studio and the NDK are installed using their default paths:
<verbatim>
    $ cd sqlite3/src/main
    $ ~/Android/Sdks/ndk-bundle/ndk-build</verbatim>
  <p> On modern hardware, this command takes roughly 2 minutes to build the
      native libraries for all Android architectures.
  <p> 
  The latest release of the public domain SQLite library comes bundled 
  with the SQLite Android bindings code downloaded in step 1. If you wish
  to use a different version of SQLite, for example one that contains the
  proprietry [./see.wiki | SEE extension], then replace the <code>sqlite3.c</code>
  and <code>sqlite3.h</code> files at the following locations before running
  the <code>ndk-build</code> command:

<verbatim>
    sqlite3/src/main/jni/sqlite/sqlite3.c
    sqlite3/src/main/jni/sqlite/sqlite3.h</verbatim>
  <p> 
  If you wish to build the SQLite library with non-standard command line
  switches, for example the -DSQLITE_ENABLE_FTS5 switch used to enable 
  <a href=http://www.sqlite.org/fts5.html>FTS5</a>, they should be added to
  the <code>Android.mk</code> file at this location:

<verbatim>
    sqlite3/src/main/jni/sqlite/Android.mk</verbatim>
  <p>
  If the <code>Android.mk</code> or <code>sqlite3.&lsp;ch&rsp;</code> files
  are edited after <code>ndk-build</code> is run, it may be necessary to run
  the <code>ndk-build clean</code> command before rerunning 
  <code>ndk-build</code> to ensure a correct build.
  <p>
  Once <code>ndk-build</code> has been run successfully, unless you modify
  the <code>Android.mk</code> or <code>sqlite3.&lsp;ch&rsp;</code> files,
  it should not be necessary to run it again. It <i>does not</i> have to be 
  run each time the application is rebuilt.

  <li> <b>Assemble the aar file</b>. To assemble the aar file using the 
  command line, first set environment variable ANDROID_HOME to the SDK
  directory, then run the gradle "assembleRelease" target from within the
  "sqlite3" sub-directory of the project directory. For example:
<verbatim>
    $ export ANDROID_HOME=~/Android/Sdk/
    $ cd sqlite3
    $ ../gradlew assembleRelease</verbatim>
  <p>
  Assembling an aar file using Android Studio is similar. Open the SQLite
  Android bindings project using Android Studio, run a "gradle sync", then
  run the "assembleRelease" gradle task within the "sqlite3" module.
  <p>
  Using either the command line or Android Studio to run the gradle task
  causes the aar file to be created at:
  <code>sqlite3/build/outputs/aar/sqlite3-release.aar</code>.
  <p>
  Once the custom aar file has been created, it may be used in an Android
  Studio application as described above. The aar file should be roughly
  3MB in size. If it is much smaller than this (closer to 100KB), this
  indicates that the aar file is missing the native libraries. The usual
  cause of this is an unnoticed error while building the native libraries 
  (step 2 above).
</ol>

<h2> <a name=directint></a> 3. Adding Source Code Directly to the Application</h2>

<p>
The SQLite Android bindings code may also be added directly to the 
application project, so that it is built and deployed in the same way 
as all other application code.

<p>
To copy the SQLite Android bindings code into an application:

<ol>
  <li> Obtain the code in the same way as [#obtaincode | described above].

  <li> Recursively copy the contents of the <code>sqlite3/main/src/jni/</code>
       directory into the application or application modules <code>jni/</code> 
       directory. Then, from the parent of the <code>jni/</code> directory, run
       the <code>ndk-build</code> command, as [#buildnative | described here]. 

  <li> Recursively copy the contents of the <code>sqlite3/main/src/java/</code>
       directory to whereever the application java code is.
</ol>

<h1>Using The SQLite Encryption Extension</h1>

<p>
  The <a href=http://www.sqlite.org/see/doc/trunk/www/readme.wiki>The SQLite Encryption Extension</a> 
  provides an easy way to create, read and write encrypted database files.
  It may be used with the SQLite Android bindings to add encrypted database
  capability to any application.

<h2> Building a SEE Enabled Version </h2>
<p>
Unless you are using a [./install.wiki#prebuilt | pre-built aar file] to use
the SEE extension with the SQLite Android bindings you will need to build
a custom version, either as a [./install.wiki#customaar | custom aar file]
or by [./install.wiki#directint|directly integrating] the code with the application.
<p>
To do this, follow the instructions linked above. Except, before running
the <code>ndk-build</code> command to build the native libraries:

<ol>
  <li> Replace the <code>sqlite3.c</code> and <code>sqlite3.h</code> files
  with the SEE enable versions (i.e. the concatenation of sqlite3.c and see.c -
  refer to the link above for details). 

  <li> Edit the Android.mk file so as to uncomment the second of the two
  lines reproduced below:

<verbatim>
  # If using SEE, uncomment the following:
  # LOCAL_CFLAGS += -DSQLITE_HAS_CODEC
</verbatim>
</ol>

<h2> Application Code Notes </h2>

<p>
  After opening or creating an encrypted database, the application must
  immediately execute a PRAGMA to configure the encryption key. This must
  be done before any other database methods are called. For example:

<verbatim>
  import org.sqlite.database.sqlite.SQLiteDatabase;

    ...

  SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase("my.db", null);
  db.execSQL("PRAGMA key = 'secretkey'");
</verbatim>

<p>
  Or, if you are using the
  <a href=http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html>SQLiteOpenHelper</a>
  helper class, the PRAGMA must be the first thing executed within the
  onConfigure() callback. For example:

<verbatim>
  import org.sqlite.database.sqlite.SQLiteDatabase;
  import org.sqlite.database.sqlite.SQLiteHelper;

    ...

  class MyHelper extends SQLiteOpenHelper {
    ...
    void onConfigure(SQLiteDatabase db){
      db.execSQL("PRAGMA key = 'secretkey'");
    }
    ...
  }
</verbatim>

<p>
  Refer to the <a href=http://www.sqlite.org/see/doc/trunk/www/readme.wiki>
  SEE documentation</a> for further details regarding encryption keys.

<p>Aside from supporting encrypted databases, SEE-enabled builds behave
differently in two more respects:

<ol>
  <li> <p>The SQLiteDatabase.<a href="http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html#enableWriteAheadLogging()">enableWriteAheadLogging()</a> method does not enable
       connection pooling. It is not possible for connection pooling to be
       used with a SEE-enabled build (even if the database is unencrypted).

  <li> <p>In Android, if database corruption is encountered, or if an attempt is
       made to open a file that is not an SQLite database, the default
       behaviour is to delete the file and create an empty database file in 
       its place. In a SEE-enabled build, the default behaviour is to throw
       an exception.<br><br>
       The reason for this is that supplying an incorrect encryption key
       is indistinguishable from opening a file that is not a database file.
       And it seems too dangerous to simply delete the file in this case.
       <br><br>
       The default behaviour can be overriden using the
       <a href="http://developer.android.com/reference/android/database/DatabaseErrorHandler.html">DatabaseErrorHandler</a> interface.
</ol>

<h1>Application Programming</h1>

<h2>Loading the Shared Library</h2>

<p>
  Before using any SQLite related methods or objects, the native SQLite
  library must be loaded into the application using the following code:

<verbatim>
  System.loadLibrary("sqliteX");
</verbatim>

<p>
  One way to ensure that the shared library is loaded early enough is
  to add it to a "static" block within the declaration of the application's
  main Activity class.

<h2>Using the SQLite Android bindings classes</h2>

<p>
  The classes that make up the built-in Android SQLite interface reside in
  the "android.database.sqlite" namespace. This interface provides all of
  the same classes, except within the "org.sqlite.database.sqlite" namespace.
  This means that to modify an application to use the custom version of 
  SQLite, all that is usually required is to replace all occurrences
  "android.database.sqlite" within the source code with
  "org.sqlite.database.sqlite". For example, the following:

<verbatim>
  import android.database.sqlite.SQLiteDatabase;
</verbatim>

<p>should be replaced with:

<verbatim>
  import org.sqlite.database.sqlite.SQLiteDatabase;
</verbatim>

<p>
  As well as replacing all uses of the classes in the 
  android.database.sqlite.* namespace, the application must also be sure 
  to use the following two:

<verbatim>
  org.sqlite.database.SQLException
  org.sqlite.database.DatabaseErrorHandler
</verbatim>

<p>instead of:

<verbatim>
  android.database.SQLException
  android.database.DatabaseErrorHandler
</verbatim>

<h2>Differences From the Built-in SQLite Support</h2>
  
<p>Aside from namespace changes, there are other differences from the
stock Android interface that applications need to be aware of:

<ol>
  <li> The SQLiteStatement.<a href="http://developer.android.com/reference/android/database/sqlite/SQLiteStatement.html#simpleQueryForBlobFileDescriptor()">simpleQueryForBlobFileDescriptor()</a> 
       API is not available.

  <li> The collation sequence "UNICODE" is not available.

  <li> The collation sequence "LOCALIZED", which normally changes with the 
       system's current locale, is always equivalent to SQLite's built
       in collation BINARY.
</ol>