Android开发系列（九）：创建数据库以及完成简单的CRUD操作

本篇博文主要实现简单的创建数据库以及实现CRUD操作。

首先，我们建立一个Android Project，命名为db

一、完成数据库的创建操作：

用SQLiteOpenHelper类中的getWritableDatabase()和getReadableDatabase()都可以获取一个操作数据库的SQLiteDatabase实例，其中getReadableDatabase()方法中会调用getWritableDatabase()方法。

区别：其中，getWritableDatabase() 方法以读写方式打开数据库，一旦数据库的磁盘空间满了，数据库就只能读而不能写，倘若使用的是getWritableDatabase() 方法就会出错。getReadableDatabase()方法则是先以读写方式打开数据库，如果数据库的磁盘空间满了，就会打开失败，当打开失败后会继续尝试以只读方式打开数据库；如果此时数据库空间出现了空余，则会成功获取一个操作数据库的SQLiteDatabase对象。

我们首先建立一个类（继承SQLiteOpenHelper）DBOpenHelper.java：

package cn.itcast.service;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteDatabase.CursorFactory;import android.database.sqlite.SQLiteOpenHelper;public class DBOpenHelper extends SQLiteOpenHelper {//构造函数，调用父类的SQLiteOpenHelper的构造函数public DBOpenHelper(Context context) {super(context, "itcast.db", null, 1);//<包>/databases/}@Overridepublic void onCreate(SQLiteDatabase db) {//是在数据库每一次被创建的时候调用的db.execSQL("CREATE TABLE person(personid integer primary key autoincrement, name varchar(20), phone VARCHAR(12) NULL)");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {//在数据库的版本发生变化时会被调用db.execSQL("ALTER TABLE person ADD amount integer");}}

onCreate()方法在初次生成数据库时才会被调用，在onCreate()方法里可以生成数据库表结构及添加一些应用使用到的初始化数据。

onUpgrade()方法在数据库的版本发生变化时会被调用，一般在软件升级时才需改变版本号，而数据库的版本是由程序员控制的。

然后，我们建立一个测试类，来实现调用DBOpenHelper中的方法来创建数据库DBTest.java：

package cn.itcast.test;public class DBTest extends AndroidTestCase {   public void testCreateDB() throws Exception{DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());dbOpenHelper.getWritableDatabase();}}

关于测试需要在AndroidManifest.xml中配置几条语句，这点不要忘了。

运行测试发现在File Explorer视图中的/data/data/cn.itcast.db/databases目录下有个itcast.db的文件，就是我们创建的数据库了。

二、完成增删改查CRUD操作：

我们用Person来做例子

首先，用建立一个javabean：Person.java

package cn.itcast.domain;public class Person {private Integer id;private String name;private String phone;private Integer amount;public Person(){}public Person(String name, String phone, Integer amount) {this.name = name;this.phone = phone;this.amount = amount;}public Person(Integer id, String name, String phone, Integer amount) {this.id = id;this.name = name;this.phone = phone;this.amount = amount;}public Integer getAmount() {return amount;}public void setAmount(Integer amount) {this.amount = amount;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}@Overridepublic String toString() {return "Person [id=" + id + ", name=" + name + ", phone=" + phone+ ", amount=" + amount + "]";}}

然后，我们需要编写业务层的类，PersonService.java

package cn.itcast.service;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import cn.itcast.domain.Person;public class PersonService {private DBOpenHelper dbOpenHelper;public PersonService(Context context) {this.dbOpenHelper = new DBOpenHelper(context);}/** * 添加记录 * @param person */public void save(Person person){SQLiteDatabase db = dbOpenHelper.getWritableDatabase();db.execSQL("insert into person(name, phone, amount) values(?,?,?)",new Object[]{person.getName(), person.getPhone(), person.getAmount()});}/** * 删除记录 * @param id 记录ID */public void delete(Integer id){SQLiteDatabase db = dbOpenHelper.getWritableDatabase();db.execSQL("delete from person where personid=?", new Object[]{id});}/** * 更新记录 * @param person */public void update(Person person){SQLiteDatabase db = dbOpenHelper.getWritableDatabase();db.execSQL("update person set name=?,phone=?,amount=? where personid=?",new Object[]{person.getName(), person.getPhone(),  person.getAmount(), person.getId()});}/** * 查询记录 * @param id 记录ID * @return */public Person find(Integer id){SQLiteDatabase db = dbOpenHelper.getReadableDatabase();Cursor cursor = db.rawQuery("select * from person where personid=?", new String[]{id.toString()});if(cursor.moveToFirst()){int personid = cursor.getInt(cursor.getColumnIndex("personid"));int amount = cursor.getInt(cursor.getColumnIndex("amount"));String name = cursor.getString(cursor.getColumnIndex("name"));String phone = cursor.getString(cursor.getColumnIndex("phone"));return new Person(personid, name, phone, amount);}cursor.close();return null;}/** * 分页获取记录 * @param offset 跳过前面多少条记录 * @param maxResult 每页获取多少条记录 * @return */public List<Person> getScrollData(int offset, int maxResult){List<Person> persons = new ArrayList<Person>();SQLiteDatabase db = dbOpenHelper.getReadableDatabase();Cursor cursor = db.rawQuery("select * from person order by personid asc limit ?,?",new String[]{String.valueOf(offset), String.valueOf(maxResult)});while(cursor.moveToNext()){int personid = cursor.getInt(cursor.getColumnIndex("personid"));int amount = cursor.getInt(cursor.getColumnIndex("amount"));String name = cursor.getString(cursor.getColumnIndex("name"));String phone = cursor.getString(cursor.getColumnIndex("phone"));persons.add(new Person(personid, name, phone, amount));}cursor.close();return persons;}/** * 分页获取记录 * @param offset 跳过前面多少条记录 * @param maxResult 每页获取多少条记录 * @return */public Cursor getCursorScrollData(int offset, int maxResult){SQLiteDatabase db = dbOpenHelper.getReadableDatabase();Cursor cursor = db.rawQuery("select personid as _id,name,phone,amount from person order by personid asc limit ?,?",new String[]{String.valueOf(offset), String.valueOf(maxResult)});return cursor;}/** * 获取记录总数 * @return */public long getCount(){SQLiteDatabase db = dbOpenHelper.getReadableDatabase();Cursor cursor = db.rawQuery("select count(*) from person", null);cursor.moveToFirst();long result = cursor.getLong(0);cursor.close();return result;}}

然后，我们就需要执行测试了PersonServiceTest.java:

package cn.itcast.test;import java.util.List;import cn.itcast.domain.Person;import cn.itcast.service.DBOpenHelper;import cn.itcast.service.PersonService;import android.test.AndroidTestCase;import android.util.Log;public class PersonServiceTest extends AndroidTestCase {private static final String TAG = "PersonServiceTest";public void testCreateDB() throws Exception{DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());dbOpenHelper.getWritableDatabase();}public void testSave() throws Exception{PersonService service = new PersonService(this.getContext());for(int i = 0 ; i < 20 ; i++){Person person = new Person("zhangxx"+ i, "136765765"+ i, 100);service.save(person);}}public void testDelete() throws Exception{PersonService service = new PersonService(this.getContext());service.delete(21);}public void testUpdate() throws Exception{PersonService service = new PersonService(this.getContext());Person person = service.find(1);person.setName("zhangxiaoxiao");service.update(person);}public void testFind() throws Exception{PersonService service = new PersonService(this.getContext());Person person = service.find(1);Log.i(TAG, person.toString());}public void testScrollData() throws Exception{PersonService service = new PersonService(this.getContext());List<Person> persons = service.getScrollData(0, 5);for(Person person : persons){Log.i(TAG, person.toString());}}public void testCount() throws Exception{PersonService service = new PersonService(this.getContext());long result = service.getCount();Log.i(TAG, result+"");}public void testUpdateAmount() throws Exception{PersonService service = new PersonService(this.getContext());Person person1 = service.find(1);Person person2 = service.find(2);person1.setAmount(100);person2.setAmount(50);service.update(person1);service.update(person2);}}

可以在找到itcast.db之后，通过下载：SQLite Explorer来打开查看