Android开发入门之数据库例子
16lz
2021-01-23
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/}@Overridepublic 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))");}@Overridepublic 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;}@Overridepublic 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 + "");}}
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