上一篇文章中介绍了手工拼写sql语句进行数据库的CRUD操作,本文将介绍调用sqlite内置的方法实现CRUD操作,其实质也是通过拼写sql语句.
首先,创建一个新的android项目:
其次,查看代码实现增删查改:
1.创建DB工具类
MyDBHelper.java(创建数据库的操作)
package com.amos.android_db;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper; /**
* Created by amosli on 14-6-12.
*/
public class MyDBHelper extends SQLiteOpenHelper{
/**
*
* @param context
*/
public MyDBHelper(Context context) {
super(context, "sqlitedb", null, 1);
} /**
* 数据库第一次创建的时候调用此方法
* @param db
*/
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table if not exists person (personid integer primary key autoincrement ,name varchar(30) ,age integer(3) )");
} @Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
2.配置测试环境
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.amos.android_db"
android:versionCode="1"
android:versionName="1.0">
<instrumentation android:name="android.test.InstrumentationTestRunner"
android:targetPackage="com.amos.android_db"/>
<uses-sdk android:minSdkVersion="7"/>
<application android:label="@string/app_name">
<uses-library android:name="android.test.runner"/>
<activity android:name="MyActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
</application>
</manifest>
3.PersonDao.java(实现增删查改的方法)
package com.amos.android_db.dao; import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import com.amos.android_db.MyDBHelper; import java.util.ArrayList;
import java.util.List; /**
* Created by amosli on 14-6-12.
*/
public class PersonDao {
private Context context;
MyDBHelper dbHelper; public PersonDao(Context context) {
this.context = context;
dbHelper = new MyDBHelper(context);
} /**
* 添加一条记录
*/
public void add(String name, int age) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
if (db.isOpen()) {
ContentValues values = new ContentValues();
values.put("age", age);
values.put("name", name);
//不允许插入一个空值,如果contentvalue,一般第二个参
db.insert("person", null, values);//通过组拼完成的添加的操作
}
db.close();
} }
１)测试add方法:
package com.amos.android_db.test; import android.test.AndroidTestCase;
import com.amos.android_db.dao.PersonDao; /**
* Created by amosli on 14-6-13.
*/
public class TestPersonDao extends AndroidTestCase{ public void testAdd() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
personDao.add("amosli",10);
personDao.add("amosli",10);
for(int i=0;i<10;i++){
personDao.add("amos"+i,10+i);
} }
}
查看结果:
打开新创建的数据库sqlitedb
./adb shell
#cd /data/data/com.amos.android_db/databases
# ls
sqlitedb
# sqlite3 sqlitedb
SQLite version 3.6.
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> .database
seq name file
--- --------------- ----------------------------------------------------------
main /data/data/com.amos.android_db/databases/sqlitedb
sqlite> .table
android_metadata person
查看写入的值:
sqlite> select * from person;
|amosli|
|amosli|
|amos0|
|amos1|
|amos2|
|amos3|
|amos4|
|amos5|
|amos6|
|amos7|
|amos8|
|amos9|
２)删除数据
delete方法,主要是调用了SQLiteDatabase的delete方法.其实质上也是在拼sql语句.
public void delete(String name) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
if (db.isOpen()) {
db.delete("person", "name=?", new String[]{name});
db.close();
}
}
测试delete方法:
public void testDelete() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
personDao.delete("amosli");
}
查看结果:
sqlite> select * from person;
|amos0|
|amos1|
|amos2|
|amos3|
|amos4|
|amos5|
|amos6|
|amos7|
|amos8|
|amos9|
3)更新数据
public void update(String name, String newname, int newage) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
if (db.isOpen()) {
ContentValues contentValues = new ContentValues();
contentValues.put("name", newname);
contentValues.put("age", newage);
db.update("person", contentValues, "name=?", new String[]{name});
db.close();
}
}
测试方法:
public void testUpdate() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
personDao.update("amos0","0amos",35);
}
查看结果:
sqlite> select * from person;
|0amos|
|amos1|
|amos2|
|amos3|
|amos4|
|amos5|
|amos6|
|amos7|
|amos8|
|amos9|
4)查找数据
public boolean find(String name) {
boolean status_result = false;
SQLiteDatabase db = dbHelper.getReadableDatabase();
// public android.database.Cursor query(
// String table,
// String[] columns,
// String selection,
// String[] selectionArgs,
// String groupBy,
// String having,
// String orderBy)
if (db.isOpen()) {
Cursor cursor = db.query("person", null, "name=?", new String[]{name}, null, null, null);
if (cursor.moveToFirst()) {
status_result = true;
}
cursor.close();
db.close();
}
return status_result;
}
测试方法:
public void testFind() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
assertEquals(true,personDao.find("amos1"));
}
5)查找所有数据
public List<Person> findAll(){
List<Person> persons = null;
SQLiteDatabase db = dbHelper.getReadableDatabase();
if(db.isOpen()){
persons = new ArrayList<Person>();
Cursor cursor = db.query("person", null, null, null, null, null, null);
while(cursor.moveToNext()){
Person person = new Person();
person.setName(cursor.getString(cursor.getColumnIndex("name")));
person.setAge(cursor.getInt(cursor.getColumnIndex("age")));
persons.add(person);
}
cursor.close();
db.close();
}
return persons;
}
测试方法:
public void testFindAll() throws Exception{
PersonDao personDao = new PersonDao(getContext());
List<Person> personList = personDao.findAll();
for(Person person:personList){
Log.d("person:",person.toString());
}
}
输出结果:
4.扩展--SQLite中的事务
这里以amos1向amos2转钱200元为例:
1),amos1账户初始1000元,amos2账户初始0元.
2),从amos1中减去200元,amos2中加上200元,这两个步骤要么同时成功,要么同时失败,不能一方成功,另一主失败,这就是事务.
代码实现:
package com.amos.android_db; import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper; /**
* Created by amosli on 14-6-12.
*/
public class MyDBHelper extends SQLiteOpenHelper{ public MyDBHelper(Context context) {
super(context, "sqlitedb", null, 2);
} /**
* 数据库第一次创建的时候调用此方法
* @param db
*/
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table if not exists person (personid integer primary key autoincrement ,name varchar(30) ,age integer(3) )");
} @Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("alter table person add account integer null");
}
}
在初始化时更新表的结构,添加account一列,用来表示账户余额.
在PersonDao中添加如下方法:
public void transferMoney() {
SQLiteDatabase db = dbHelper.getWritableDatabase();
if(db.isOpen()){
try{
db.beginTransaction();
//给amos1账户里设置1000元,amost account=0;
db.execSQL("update person set account=? where name = ?",new Object[]{1000,"amos1"});
db.execSQL("update person set account=? where name = ?",new Object[]{0,"amos2"});
//从amos1账户里扣除200元
db.execSQL("update person set account=account-? where name = ?",new Object[]{200,"amos1"});
//把amos1的钱转给amos2
db.execSQL("update person set account=account+? where name=?",new Object[]{200,"amos2"});
}catch(Exception e){
e.printStackTrace();
}finally{
//显示的设置数据事务是否成功
db.setTransactionSuccessful();
db.endTransaction();
db.close();
}
}
}
和hibernate里的事务调用很类似,这里先beginTransaction,然后要注意的是setTransactionSuccessful和endTransaction.
测试方法:
public void testTransaction() throws Exception{
PersonDao personDao = new PersonDao(getContext());
personDao.transferMoney();
}
测试结果:
sqlite> select * from person;
|0amos||
|amos1||
|amos2||
|amos3||
|amos4||
|amos5||
|amos6||
|amos7||
|amos8||
|amos9||
本文源码:https://github.com/amosli/android_basic/tree/android_db