Android SQLite事务

介绍一个ORM框架，LitePal。
GitHub：https://github.com/LitePalFramework/LitePal
使用方法很简单，导入xx包就不说了。

1. 创建一个类，继承DataSupport。

public class StudentBean extends DataSupport {

    private int studentID;
    private String studentName;
    private String studentAge;
    private String studentSex;
    private String studentPhone;

    public int getStudentID() {
        return studentID;
    }

    public void setStudentID(int studentID) {
        this.studentID = studentID;
    }

    public String getStudentName() {
        return studentName;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public String getStudentAge() {
        return studentAge;
    }

    public void setStudentAge(String studentAge) {
        this.studentAge = studentAge;
    }

    public String getStudentSex() {
        return studentSex;
    }

    public void setStudentSex(String studentSex) {
        this.studentSex = studentSex;
    }

    public String getStudentPhone() {
        return studentPhone;
    }

    public void setStudentPhone(String studentPhone) {
        this.studentPhone = studentPhone;
    }
}

2. assets目录下创建一个名为litepal.xml的配置文件

<?xml version="1.0" encoding="utf-8"?>
<litepal>
    <dbname value="litepal" >
    </dbname>
    <version value="3" >
    </version>
    <list>
         <mapping class="com.jeremy.universal_android.sqlite.bean.StudentBean"></mapping>
    </list>
</litepal>

3. application继承LitePalApplication

public class UniversalAndroidApplication extends LitePalApplication {
    @Override
    public void onCreate() {
        super.onCreate();
//        初始化sqlite库
        LitePalApplication.initialize(this);
    }
}

如何使用？

private void insertWithTs() {
    StudentBean studentBean = null;

    for (int i = 0; i < 1000; i++) {
        studentBean = new StudentBean();

        studentBean.setStudentName("小明" + i);
        studentBean.setStudentAge("" + i);

        studentBean.save();
    }
}

private void insertWithoutTs() {

    List<StudentBean> studentBeanList = new ArrayList<>();

    StudentBean studentBean = null;

    for (int i = 0; i < 1000; i++) {
        studentBean = new StudentBean();

        studentBean.setStudentName("小明" + i);
        studentBean.setStudentAge("" + i);

        studentBeanList.add(studentBean);
    }

    DataSupport.saveAll(studentBeanList);
}

问题来了，上面两个方法同样是插入1000条数据，区别是什么呢？insertWithTs()调用的是对象的save()，执行1000次；而insertWithoutTs()是把1000个对象放在一个集合中，最后调用一次saveAll()。

看一下两种方法效率如何。
insertWithTs()，单位是毫秒

E/SQLITE: begin --> 1470285148375
E/SQLITE: end --> 1470285156347
E/SQLITE: gap --> 7972

insertWithoutTs()，单位是毫秒

E/SQLITE: begin --> 1470285043075
E/SQLITE: end --> 1470285045001
E/SQLITE: gap --> 1926

差别如此之大，原因在哪里？看源码
save()方法是这样的

public synchronized void saveThrows() {
    SQLiteDatabase db = Connector.getDatabase();
    db.beginTransaction();
    try {
        // some code
        db.setTransactionSuccessful();
    } catch (Exception e) {
        throw new DataSupportException(e.getMessage());
    } finally {
        db.endTransaction();
    }
}

而saveAll()呢？

public static synchronized <T extends DataSupport> void saveAll(Collection<T> collection) {
    SQLiteDatabase db = Connector.getDatabase();
    db.beginTransaction();
    try {
        //code to save collection
        db.setTransactionSuccessful();
    } catch (Exception e) {
        throw new DataSupportException(e.getMessage());
    } finally {
        db.endTransaction();
    }
}

每一次save()都涉及到一个事务的begin和end，当数据量变大时，代码执行效率就会明显低于saveAll()的方式。另外需要注意的是，数据插入属于耗时操作，应开启线程。