Android开发入门之数据库例子
第一步：新建一个Android工程命名为db目录结构如下图：
第二步：在cn.leigo.service包下新建DBOpenHelper类，该类继承自DBOpenHelper如下：
package cn.leigo.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper {
public DBOpenHelper(Context context) {
super(context, "leigo.db", null, 2); //<包>/databases/
}
@Override
public void onCreate(SQLiteDatabase db) {// 数据库第一次被创建的时候调用的
db.execSQL("CREATE TABLE person (personid integer primary key autoincrement, name varchar(20))");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("ALTER TABLE person ADD phone VARCHAR(12) NULL");
}
}
第三步：引入测试类，在cn.leigo.test包下新建PersonServiceTest类，该类继承AndroidTestCase：
package cn.leigo.test;
import cn.leigo.service.DBOpenHelper;
import android.test.AndroidTestCase;
public class PersonServiceTest extends AndroidTestCase {
public void testCreateDB() throws Exception {
DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
dbOpenHelper.getWritableDatabase();
}
}
右键Outline视图中的PersonServiceTest,Run as ->Android JUnit Test
运行成功！
在File Explorer中找到该数据库文件
我们可以看到数据库字段已经创建成功了，将数据库文件导出到桌面上然后打开
同时android自动帮你生成了一张名为android_metadata的表，该表存储了所使用的语言信息
现在我们将数据库的版本升级为2，然后再进行测试，此时只会调用onUpgrade方法,我们看到结果如下：
下面到SQLiteOpenHelper源码下查看它是怎样实现的
/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.database.sqlite;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.util.Log;
/**
* A helper class to manage database creation and version management.
*
* <p>You create a subclass implementing {@link #onCreate}, {@link #onUpgrade} and
* optionally {@link #onOpen}, and this class takes care of opening the database
* if it exists, creating it if it does not, and upgrading it as necessary.
* Transactions are used to make sure the database is always in a sensible state.
*
* <p>This class makes it easy for {@link android.content.ContentProvider}
* implementations to defer opening and upgrading the database until first use,
* to avoid blocking application startup with long-running database upgrades.
*
* <p>For an example, see the NotePadProvider class in the NotePad sample application,
* in the <em>samples/</em> directory of the SDK.</p>
*
* <p class="note"><strong>Note:</strong> this class assumes
* monotonically increasing version numbers for upgrades. Also, there
* is no concept of a database downgrade; installing a new version of
* your app which uses a lower version number than a
* previously-installed version will result in undefined behavior.</p>
*/
public abstract class SQLiteOpenHelper {
private static final String TAG = SQLiteOpenHelper.class.getSimpleName();
private final Context mContext;
private final String mName;
private final CursorFactory mFactory;
private final int mNewVersion;
private SQLiteDatabase mDatabase = null;
private boolean mIsInitializing = false;
/**
* Create a helper object to create, open, and/or manage a database.
* This method always returns very quickly. The database is not actually
* created or opened until one of {@link #getWritableDatabase} or
* {@link #getReadableDatabase} is called.
*
* @param context to use to open or create the database
* @param name of the database file, or null for an in-memory database
* @param factory to use for creating cursor objects, or null for the default
* @param version number of the database (starting at 1); if the database is older,
* {@link #onUpgrade} will be used to upgrade the database
*/
public SQLiteOpenHelper(Context context, String name, CursorFactory factory, int version) {
if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version);
mContext = context;
mName = name;
mFactory = factory;
mNewVersion = version;
}
/**
* Create and/or open a database that will be used for reading and writing.
* The first time this is called, the database will be opened and
* {@link #onCreate}, {@link #onUpgrade} and/or {@link #onOpen} will be
* called.
*
* <p>Once opened successfully, the database is cached, so you can
* call this method every time you need to write to the database.
* (Make sure to call {@link #close} when you no longer need the database.)
* Errors such as bad permissions or a full disk may cause this method
* to fail, but future attempts may succeed if the problem is fixed.</p>
*
* <p class="caution">Database upgrade may take a long time, you
* should not call this method from the application main thread, including
* from {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.
*
* @throws SQLiteException if the database cannot be opened for writing
* @return a read/write database object valid until {@link #close} is called
*/
public synchronized SQLiteDatabase getWritableDatabase() {
if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
return mDatabase; // The database is already open for business
}
if (mIsInitializing) {
throw new IllegalStateException("getWritableDatabase called recursively");
}
// If we have a read-only database open, someone could be using it
// (though they shouldn't), which would cause a lock to be held on
// the file, and our attempts to open the database read-write would
// fail waiting for the file lock. To prevent that, we acquire the
// lock on the read-only database, which shuts out other users.
boolean success = false;
SQLiteDatabase db = null;
if (mDatabase != null) mDatabase.lock();
try {
mIsInitializing = true;
if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
db = mContext.openOrCreateDatabase(mName, 0, mFactory);
}
int version = db.getVersion();
if (version != mNewVersion) {
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
if (version > mNewVersion) {
Log.wtf(TAG, "Can't downgrade read-only database from version " +
version + " to " + mNewVersion + ": " + db.getPath());
}
onUpgrade(db, version, mNewVersion);
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
onOpen(db);
success = true;
return db;
} finally {
mIsInitializing = false;
if (success) {
if (mDatabase != null) {
try { mDatabase.close(); } catch (Exception e) { }
mDatabase.unlock();
}
mDatabase = db;
} else {
if (mDatabase != null) mDatabase.unlock();
if (db != null) db.close();
}
}
}
/**
* Create and/or open a database. This will be the same object returned by
* {@link #getWritableDatabase} unless some problem, such as a full disk,
* requires the database to be opened read-only. In that case, a read-only
* database object will be returned. If the problem is fixed, a future call
* to {@link #getWritableDatabase} may succeed, in which case the read-only
* database object will be closed and the read/write object will be returned
* in the future.
*
* <p class="caution">Like {@link #getWritableDatabase}, this method may
* take a long time to return, so you should not call it from the
* application main thread, including from
* {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}.
*
* @throws SQLiteException if the database cannot be opened
* @return a database object valid until {@link #getWritableDatabase}
* or {@link #close} is called.
*/
public synchronized SQLiteDatabase getReadableDatabase() {
if (mDatabase != null && mDatabase.isOpen()) {
return mDatabase; // The database is already open for business
}
if (mIsInitializing) {
throw new IllegalStateException("getReadableDatabase called recursively");
}
try {
return getWritableDatabase();
} catch (SQLiteException e) {
if (mName == null) throw e; // Can't open a temp database read-only!
Log.e(TAG, "Couldn't open " + mName + " for writing (will try read-only):", e);
}
SQLiteDatabase db = null;
try {
mIsInitializing = true;
String path = mContext.getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory, SQLiteDatabase.OPEN_READONLY);
if (db.getVersion() != mNewVersion) {
throw new SQLiteException("Can't upgrade read-only database from version " +
db.getVersion() + " to " + mNewVersion + ": " + path);
}
onOpen(db);
Log.w(TAG, "Opened " + mName + " in read-only mode");
mDatabase = db;
return mDatabase;
} finally {
mIsInitializing = false;
if (db != null && db != mDatabase) db.close();
}
}
/**
* Close any open database object.
*/
public synchronized void close() {
if (mIsInitializing) throw new IllegalStateException("Closed during initialization");
if (mDatabase != null && mDatabase.isOpen()) {
mDatabase.close();
mDatabase = null;
}
}
/**
* Called when the database is created for the first time. This is where the
* creation of tables and the initial population of the tables should happen.
*
* @param db The database.
*/
public abstract void onCreate(SQLiteDatabase db);
/**
* Called when the database needs to be upgraded. The implementation
* should use this method to drop tables, add tables, or do anything else it
* needs to upgrade to the new schema version.
*
* <p>The SQLite ALTER TABLE documentation can be found
* <a href="http://sqlite.org/lang_altertable.html">here</a>. If you add new columns
* you can use ALTER TABLE to insert them into a live table. If you rename or remove columns
* you can use ALTER TABLE to rename the old table, then create the new table and then
* populate the new table with the contents of the old table.
*
* @param db The database.
* @param oldVersion The old database version.
* @param newVersion The new database version.
*/
public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion);
/**
* Called when the database has been opened. The implementation
* should check {@link SQLiteDatabase#isReadOnly} before updating the
* database.
*
* @param db The database.
*/
public void onOpen(SQLiteDatabase db) {}
}
以m开头的蓝色变量都是成员(member)变量
在源码getWritableDatabase()方法中
if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
db = mContext.openOrCreateDatabase(mName, 0, mFactory);
}
判断数据库的名称是否为空，如果是则调用create()方法，否则调用
openOrCreateDatabase(mName, 0, mFactory)
方法，第二个参数为模式
第一次调用时，数据库默认版本为0，而我们传入的版本为1，调用onCreate(db);这个方法
，这里还用到了数据库事务。
下面来实现数据的增删改查操作，新建Person类，该类在cn.leigo.domain包下
package cn.leigo.domain;
public class Person {
private Integer id;
private String name;
private String phone;
public Person() {
}
public Person(String name, String phone) {
super();
this.name = name;
this.phone = phone;
}
public Person(Integer id, String name, String phone) {
super();
this.id = id;
this.name = name;
this.phone = phone;
}
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;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", phone=" + phone + "]";
}
}
在 cn.leigo.service下新建PersonService类,此业务类处理增删改查
package cn.leigo.service;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.leigo.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) VALUES(?,?)", new Object[] {
person.getName(), person.getPhone() });
db.close();
}
/**
* 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 });
db.close();
}
/**
* 更新记录
* @param person
*/
public void update(Person person) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
db.execSQL(
"UPDATE person SET name=?,phone=? WHERE personid=?",
new Object[] { person.getName(), person.getPhone(),
person.getId() });
db.close();
}
/**
* 查找记录
* @param id 记录ID
* @return
*/
public Person find(Integer id) {
Person person = null;
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM person WHERE personid=?",
new String[] { id + "" });
if (cursor.moveToFirst()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
}
cursor.close();
db.close();
return person;
}
/**
* 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) {
Person person = null;
List<Person> persons = new ArrayList<Person>();
;
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery(
"SELECT * FROM person order by personid asc limit ?,?",
new String[] { offset + "", maxResult + "" });
while (cursor.moveToNext()) {
int id = cursor.getInt(cursor.getColumnIndex("personid"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
persons.add(person);
}
cursor.close();
db.close();
return persons;
}
/**
* 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 count = cursor.getLong(0);
cursor.close();
db.close();
return count;
}
}
package cn.leigo.service;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.leigo.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) VALUES(?,?)", new Object[] {
person.getName(), person.getPhone() });
db.close();
}
/**
* 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 });
db.close();
}
/**
* 更新记录
* @param person
*/
public void update(Person person) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
db.execSQL(
"UPDATE person SET name=?,phone=? WHERE personid=?",
new Object[] { person.getName(), person.getPhone(),
person.getId() });
db.close();
}
/**
* 查找记录
* @param id 记录ID
* @return
*/
public Person find(Integer id) {
Person person = null;
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM person WHERE personid=?",
new String[] { id + "" });
if (cursor.moveToFirst()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
}
cursor.close();
db.close();
return person;
}
/**
* 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) {
Person person = null;
List<Person> persons = new ArrayList<Person>();
;
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery(
"SELECT * FROM person order by personid asc limit ?,?",
new String[] { offset + "", maxResult + "" });
while (cursor.moveToNext()) {
int id = cursor.getInt(cursor.getColumnIndex("personid"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
persons.add(person);
}
cursor.close();
db.close();
return persons;
}
/**
* 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 count = cursor.getLong(0);
cursor.close();
db.close();
return count;
}
}
然后进行测试:
增：
public void testSave() throws Exception {
PersonService service = new PersonService(getContext());
Person person = new Person("zhangsan", "18900000000");
service.save(person);
}
查：
public void testFind() throws Exception {
PersonService service = new PersonService(getContext());
Person person = service.find(1);
Log.d(TAG, person.toString());
}
改:
public void testUpdate() throws Exception {
PersonService service = new PersonService(getContext());
Person person = service.find(1);
person.setPhone("15100000000");
service.update(person);
}
统计条数:
public void testGetCount() throws Exception {
PersonService service = new PersonService(getContext());
long count = service.getCount();
Log.d(TAG, count + "");
}
public void testSave() throws Exception {
PersonService service = new PersonService(getContext());
for (int i = 0; i < 20; i++) {
Person person = new Person("test" + i, "1890000000" + i);
service.save(person);
}
}
再来进行一次统计
分页：
public void testGetScrollData() throws Exception {
PersonService service = new PersonService(getContext());
List<Person> persons = service.getScrollData(0, 5);
for (Person person : persons) {
Log.d(TAG, person.toString());
}
}
删：
public void testDelete() throws Exception {
PersonService service = new PersonService(getContext());
service.delete(21);
}
增删改查另外一种方法：
package cn.leigo.service;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.leigo.domain.Person;
public class OtherPersonService {
private DBOpenHelper dbOpenHelper;
public OtherPersonService(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) VALUES(?,?)", new
// Object[] {
// person.getName(), person.getPhone() });
ContentValues values = new ContentValues();
values.put("name", person.getName());
values.put("phone", person.getPhone());
db.insert("person", null, values);
db.close();
}
/**
* 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
// });
db.delete("person", "personid=?", new String[] { id + "" });
db.close();
}
/**
* 更新记录
*
* @param person
*/
public void update(Person person) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
// db.execSQL(
// "UPDATE person SET name=?,phone=? WHERE personid=?",
// new Object[] { person.getName(), person.getPhone(),
// person.getId() });
ContentValues values = new ContentValues();
values.put("name", person.getName());
values.put("phone", person.getPhone());
db.update("person", values, "personid=?", new String[] { person.getId()
+ "" });
db.close();
}
/**
* 查找记录
*
* @param id
* 记录ID
* @return
*/
public Person find(Integer id) {
Person person = null;
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
// Cursor cursor = db.rawQuery("SELECT * FROM person WHERE personid=?",
// new String[] { id + "" });
Cursor cursor = db.query("person", null, "personid=?",
new String[] { id + "" }, null, null, null);
if (cursor.moveToFirst()) {
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
}
cursor.close();
db.close();
return person;
}
/**
* 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) {
Person person = null;
List<Person> persons = new ArrayList<Person>();
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
// Cursor cursor = db.rawQuery(
// "SELECT * FROM person order by personid asc limit ?,?",
// new String[] { offset + "", maxResult + "" });
Cursor cursor = db.query("person", null, null, null, null, null,
"personid asc", offset + "," + maxResult);
while (cursor.moveToNext()) {
int id = cursor.getInt(cursor.getColumnIndex("personid"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
person = new Person(id, name, phone);
persons.add(person);
}
cursor.close();
db.close();
return persons;
}
/**
* 获取记录总数
*
* @return
*/
public long getCount() {
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
// Cursor cursor = db.rawQuery("SELECT count(*) FROM person", null);
Cursor cursor = db.query("person", new String[] { "count(*)" }, null,
null, null, null, null);
cursor.moveToFirst();
long count = cursor.getLong(0);
cursor.close();
db.close();
return count;
}
}
测试类：
package cn.leigo.test;
import java.util.List;
import android.test.AndroidTestCase;
import android.util.Log;
import cn.leigo.domain.Person;
import cn.leigo.service.DBOpenHelper;
import cn.leigo.service.OtherPersonService;
public class OtherPersonServiceTest extends AndroidTestCase {
private static final String TAG = "OtherPersonServiceTest";
public void testCreateDB() throws Exception {
DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
dbOpenHelper.getWritableDatabase();
}
public void testSave() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
Person person = new Person("leigo", "13500000000");
service.save(person);
}
public void testDelete() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
service.delete(22);
}
public void testUpdate() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
Person person = service.find(1);
person.setPhone("151023000000");
service.update(person);
}
public void testFind() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
Person person = service.find(22);
Log.d(TAG, person.toString());
}
public void testGetScrollData() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
List<Person> persons = service.getScrollData(5, 5);
for (Person person : persons) {
Log.d(TAG, person.toString());
}
}
public void testGetCount() throws Exception {
OtherPersonService service = new OtherPersonService(getContext());
long count = service.getCount();
Log.d(TAG, count + "");
}
}