Litpal数据库的使用
1首先在build.gradle中加入compile 'org.litpal.android:core:1.4.1'
2在src/main目录中NEW-Directory，创建assessts目录，新建一个litepal.xml文件，如下所示：
<litepal>
<dbname value="BookStore"></dbname>
<version value = "2"></version>
<list>
<mapping class="com.example.litepaltest.Book"></mapping>
</list>
</litpal>
3需要Application中继承LitePalApplication
4创建和升级数据库
public class Book{
private int id;
public int getId(注意大写){
return id;
}
public void setId(int id){
this.id = id;
}
}
5添加数据：
Book book = new Book();
book.setName("sadsada");
book.save();
6更新数据：
Book book = new Book();
book.setName("sadsada");
book.updateAll("name=? and author = ?","dasd","das");
7列数据变成默认值
Book book = new Book();
book.setToDefault("pages");
book.updateAll();
8删除数据
DataSupport.deleteAll(Book.class,"price < ?","15");
deleteAll()如果不指定约束条件，意味删除所有数据
9查询数据
（1）查询所有数据：List<Book> books = DataSupport.findAll(Book.class);
(2)查询第一条数据：DataSupport.findFirst(Book.class);
(3)查询最后一条数据：DataSupport.findLast(Book.class);
(4)查询那几列的数据：DataSupport.select("name","author").find(Book.class);
(5)查询约束条件:DataSupport.where("page > ?","400").find(Book.class);
(6)查询排序：DataSupport.order("price desc").find(Book.class);降序
asc或者不屑标示降序
(7)只查询表前三条数据：DataSupport.limit(3).find(Book.class)
(8)指定查询结果的偏移量：查询2、3、4条数据
DataSupport.limit(3).offset(1).find(Book.class);
(9)组合查询：Datasupport.select("name","author","pages").where("page > ?","400").order("pages").limit(10).offest(10).find(Book.class);查询11到22条数，页数大于400这个条件