Android学习---SQLite数据库的增删改查和事务(transaction)调用

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