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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) { } }
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PersonDao.java (实现增删改查)
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(); } }
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测试添加方法
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); } }
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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"); }
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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update
public void testUpdate() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
personDao.update("amos0","0amos",35);
}
- 查询数据
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select
public void testFind() throws Exception{
PersonDao personDao = new PersonDao(this.getContext());
assertEquals(true,personDao.find("amos1"));
}
- 查询所有数据
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
public void testFindAll() throws Exception{
PersonDao personDao = new PersonDao(getContext());
List<Person> personList = personDao.findAll();
for(Person person:personList){
Log.d("person:",person.toString());
}
}
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扩展 (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:升级数据库
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(); } } }
这里先beginTransaction,然后要注意的是setTransactionSuccessful和endTransaction.
public void testTransaction() throws Exception{ PersonDao personDao = new PersonDao(getContext()); personDao.transferMoney(); }