Android中简便使用数据库的方法：LitePal的使用方法

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An Android library that makes developers use SQLite database extremely easy.

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README.md

LitePal for Android

LitePal is an open source Android library that allows developers to use SQLite database extremely easy. You can finish most of the database operations without writing even a SQL statement, including create or upgrade tables, crud operations, aggregate functions, etc. The setup of LitePal is quite simple as well, you can integrate it into your project in less than 5 minutes.

Experience the magic right now and have fun!

Features

Using object-relational mapping (ORM) pattern.
Almost zero-configuration(only one configuration file with few properties).
Maintains all tables automatically(e.g. create, alter or drop tables).
Multi databases supported.
Encapsulated APIs for avoiding writing SQL statements.
Awesome fluent query API.
Alternative choice to use SQL still, but easier and better APIs than the originals.
More for you to explore.

Latest Downloads

litepal-1.5.1.jar (library contains *.class files)
litepal-1.5.1-src.jar (library contains *.class files and *.java files)

Quick Setup

1. Include library

Using Eclipse

Download the latest jar in the above section. Or browse all versions here to choose one to download.
Put the jar into libs folder of your Android project.

Using Android Studio

Edit your build.gradle file and add below dependency:

dependencies {    compile 'org.litepal.android:core:1.5.1'}

2. Configure litepal.xml

Create a file in the assets folder of your project and name it as litepal.xml. Then copy the following codes into it.

<?xml version="1.0" encoding="utf-8"?><litepal>    <!--    Define the database name of your application.     By default each database name should be end with .db.     If you didn't name your database end with .db,     LitePal would plus the suffix automatically for you.    For example:        <dbname value="demo" />    -->    <dbname value="demo" />    <!--    Define the version of your database. Each time you want     to upgrade your database, the version tag would helps.    Modify the models you defined in the mapping tag, and just     make the version value plus one, the upgrade of database    will be processed automatically without concern.For example:        <version value="1" />    -->    <version value="1" />    <!--    Define your models in the list with mapping tag, LitePal will    create tables for each mapping class. The supported fields    defined in models will be mapped into columns.    For example:        <list>    <mapping class="com.test.model.Reader" />    <mapping class="com.test.model.Magazine" />    </list>    -->    <list>    </list>        <!--        Define where the .db file should be. "internal" means the .db file        will be stored in the database folder of internal storage which no        one can access. "external" means the .db file will be stored in the        path to the directory on the primary external storage device where        the application can place persistent files it owns which everyone        can access. "internal" will act as default.        For example:        <storage value="external" />    -->    </litepal>

This is the only configuration file, and the properties are simple.

dbname configure the database name of project.
version configure the version of database. Each time you want to upgrade database, plus the value here.
list configure the mapping classes.
storage configure where the database file should be stored. internal and external are the only valid options.

3. Configure LitePalApplication

You don't want to pass the Context param all the time. To makes the APIs simple, just configure the LitePalApplication in AndroidManifest.xml as below:

<manifest>    <application        android:name="org.litepal.LitePalApplication"        ...    >        ...    </application></manifest>

Of course you may have your own Application and has already configured here, like:

<manifest>    <application        android:name="com.example.MyOwnApplication"        ...    >        ...    </application></manifest>

That's OK. LitePal can still live with that. Just call LitePal.initialize(context) in your own Application:

public class MyOwnApplication extends AnotherApplication {    @Override    public void onCreate() {        super.onCreate();        LitePal.initialize(this);    }    ...}

Make sure to call this method as early as you can. In the onCreate() method of Application will be fine. And always remember to use the application context as parameter. Do not use any instance of activity or service as parameter, or memory leaks might happen.

Get Started

After setup, you can experience the powerful function now.

1. Create tables

Define the models first. For example you have two models, Album and Song. The models can be defined as below:

public class Album extends DataSupport {    @Column(unique = true, defaultValue = "unknown")    private String name;    private float price;    private byte[] cover;    private List<Song> songs = new ArrayList<Song>();    // generated getters and setters.    ...}

public class Song extends DataSupport {    @Column(nullable = false)    private String name;    private int duration;    @Column(ignore = true)    private String uselessField;    private Album album;    // generated getters and setters.    ...}

Then add these models into the mapping list in litepal.xml:

<list>    <mapping class="org.litepal.litepalsample.model.Album" />    <mapping class="org.litepal.litepalsample.model.Song" /></list>

OK! The tables will be generated next time you operate database. For example, gets the SQLiteDatabase with following codes:

SQLiteDatabase db = LitePal.getDatabase();

Now the tables will be generated automatically with SQLs like this:

CREATE TABLE album (id integer primary key autoincrement,name text unique default 'unknown',price real,cover blob);CREATE TABLE song (id integer primary key autoincrement,name text not null,duration integer,album_id integer);

2. Upgrade tables

Upgrade tables in LitePal is extremely easy. Just modify your models anyway you want:

public class Album extends DataSupport {    @Column(unique = true, defaultValue = "unknown")    private String name;    @Column(ignore = true)    private float price;    private byte[] cover;    private Date releaseDate;    private List<Song> songs = new ArrayList<Song>();    // generated getters and setters.    ...}

A releaseDate field was added and price field was annotated to ignore. Then increase the version number in litepal.xml:

<!--    Define the version of your database. Each time you want     to upgrade your database, the version tag would helps.    Modify the models you defined in the mapping tag, and just     make the version value plus one, the upgrade of database    will be processed automatically without concern.    For example:        <version value="1" ></version>--><version value="2" ></version>

The tables will be upgraded next time you operate database. A releasedate column will be added into album table and the original price column will be removed. All the data in album table except those removed columns will be retained.

But there are some upgrading conditions that LitePal can't handle and all data in the upgrading table will be cleaned:

Add a field which annotated as unique = true.
Change a field's annotation into unique = true.
Change a field's annotation into nullable = false.

Be careful of the above conditions which will cause losing data.

3. Save data

The saving API is quite object oriented. Each model which inherits from DataSupport would have the save() method for free:

Album album = new Album();album.setName("album");album.setPrice(10.99f);album.setCover(getCoverImageBytes());album.save();Song song1 = new Song();song1.setName("song1");song1.setDuration(320);song1.setAlbum(album);song1.save();Song song2 = new Song();song2.setName("song2");song2.setDuration(356);song2.setAlbum(album);song2.save();

This will insert album, song1 and song2 into database with associations.

4. Update data

The simplest way, use save() method to update a record found by find():

Album albumToUpdate = DataSupport.find(Album.class, 1);albumToUpdate.setPrice(20.99f); // raise the pricealbumToUpdate.save();

Each model which inherits from DataSupport would also have update() and updateAll() method. You can update a single record with a specified id:

Album albumToUpdate = new Album();albumToUpdate.setPrice(20.99f); // raise the pricealbumToUpdate.update(id);

Or you can update multiple records with a where condition:

Album albumToUpdate = new Album();albumToUpdate.setPrice(20.99f); // raise the pricealbumToUpdate.updateAll("name = ?", "album");

5. Delete data

You can delete a single record using the static delete() method in DataSupport:

DataSupport.delete(Song.class, id);

Or delete multiple records using the static deleteAll() method in DataSupport:

DataSupport.deleteAll(Song.class, "duration > ?" , "350");

6. Query data

Find a single record from song table with specified id:

Song song = DataSupport.find(Song.class, id);

Find all records from song table:

List<Song> allSongs = DataSupport.findAll(Song.class);

Constructing complex query with fluent query:

List<Song> songs = DataSupport.where("name like ?", "song%").order("duration").find(Song.class);

7. Async operations

Every database operation is on main thread by default. If your operation might spent a long time, for example saving or querying tons of records. You may want to use async operations.

LitePal support async operations on all crud methods. If you want to find all records from song table on a background thread, use codes like this:

DataSupport.findAllAsync(Song.class).listen(new FindMultiCallback() {    @Override    public <T> void onFinish(List<T> t) {        List<Song> allSongs = (List<Song>) t;    }});

Just use findAllAsync() instead of findAll(), and append a listen() method, the finding result will be callback to onFinish() method once it finished.

Abd saving asynchronously is quite the same:

Album album = new Album();album.setName("album");album.setPrice(10.99f);album.setCover(getCoverImageBytes());album.saveAsync().listen(new SaveCallback() {    @Override    public void onFinish(boolean success) {    }});

Just use saveAsync() instead of save(). It will save Album into database on a background, and the saving result will be callback to onFinish() method.

8. Multiple databases

If your app needs multiple databases, LitePal support it completely. You can create as many databases as you want at runtime. For example:

LitePalDB litePalDB = new LitePalDB("demo2", 1);litePalDB.addClassName(Singer.class.getName());litePalDB.addClassName(Album.class.getName());litePalDB.addClassName(Song.class.getName());LitePal.use(litePalDB);

This will create a demo2 database with singer, album and song tables.

If you just want to create a new database but with same configuration as litepal.xml, you can do it with:

LitePalDB litePalDB = LitePalDB.fromDefault("newdb");LitePal.use(litePalDB);

You can always switch back to default database with:

LitePal.useDefault();

And you can delete any database by specified database name:

LitePal.deleteDatabase("newdb");

ProGuard

If you are using ProGuard you might need to add the following option:

-keep class org.litepal.** {    *;}-keep class * extends org.litepal.crud.DataSupport {    *;}

Developed By

Tony Green

Sample App

The sample app has been published onto Google Play for easy access.

Get it on:

Bugs Report

If you find any bug when using LitePal, please report here. Thanks for helping us making better.

Change logs

1.5.1

Support async operations for all crud methods.
Add saveOrUpdate() method in DataSupport.
Fix known bugs.

1.4.1

Fix bug of DateSupport.count error.
Fix bug of losing blob data when upgrading database.
Fix other known bugs.

1.4.0

Support multiple databases.
Support crud operations for generic collection data in models.
Add SQLite keywords convert function to avoid keywords conflict.
Fix known bugs.

1.3.2

Improve an outstanding speed up of querying and saving.
Support to store database file in external storage.
Support to mapping fields which inherit from superclass.
Add findFirst() and findLast() in fluent query.
Add isExist() and saveIfNotExist() method in DataSupport.

1.3.1

Support storing binary data. Byte array field will be mapped into database as blob type.
Add saveFast() method in DataSupport. If your model has no associations to handle, use saveFast() method will be much more efficient.
Improve query speed with optimized algorithm.

1.3.0

Add annotation functions to declare unique, not null and default constraints.
Remove the trick of ignore mapping fields with non-private modifier.
Support to use annotation to ignore mapping fields with ignore = true
Add some magical methods in DataSupport for those who understand LitePal deeper.
Fix known bugs.

License

Copyright (C)  Tony Green, LitePal Framework Open Source ProjectLicensed under the Apache License, Version 2.0 (the "License");you may not use this file except in compliance with the License.You may obtain a copy of the License at     http://www.apache.org/licenses/LICENSE-2.0Unless required by applicable law or agreed to in writing, softwaredistributed under the License is distributed on an "AS IS" BASIS,WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.See the License for the specific language governing permissions andlimitations under the License.

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