Android 数据存储之 SQLite

数据存储在开发中是使用最频繁的，在这里主要介绍Android平台中实现数据存储的5种方式，分别是：

1 使用SharedPreferences存储数据

2 文件存储数据

3 SQLite数据库存储数据

4 使用ContentProvider存储数据

5 网络存储数据

本文介绍SQLite存储方法，

在Android平台上，集成了一个嵌入式关系型数据库-SQLite，SQLite3支持null，integer，real，text和blob数据类型，虽然支持的数据类型只有5种，但是实际上也接受varchar，char，decimal等数据类型，只是在运算和保持时会转化成相对应的5种数据类型，SQLite可以把任何类型存储在任意字段上，但是定义为integer
primary key的字段只能是64为整数，并且SQLite支持大部分标准的sql语句

第一步我写一个类继承 SQLiteOpenHelper来实现数据库的操作

public class DBOpenHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME="mydb.db";
private static final int DATABASE_VERSION = 1;
private static final String DICTIONARY_TABLE_NAME = "dictionary";
private static final String DICTIONARY_TABLE_CREATE = "CREATE TABLE " + DICTIONARY_TABLE_NAME + " ( KEY_WORD TEXT, KEY_DEFINITION TEXT);";
private static final String PERSON_TABLE_CREATE = "create table person(id integer primary key autoincrement,name varchar(64),address varchar(64),sex varchar(4))";
public DBOpenHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

/**
* 当数据库创建的时候，是第一次被执行,完成对数据库的表的创建
* //支持的数据类型：整型数据，字符串类型，日期类型，二进制的数据类型，
* 可以说无数据类型
*/
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DICTIONARY_TABLE_CREATE);
db.execSQL(PERSON_TABLE_CREATE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String sql = "alter table person add sex varchar(8)";
db.execSQL(sql);
}

}


数据的添删改查分别可以通过2种途径来实现

数据的添加

1.使用insert方法

2.使用execSQL方式来实现

数据的删除

同样有2种方式可以实现

使用execSQL方式的实现

数据修改

同上，仍是2种方式

使用execSQL方式的实现

数据查询

数据查询相对前面几种方法就复杂一些了，因为查询会带有很多条件

通过query实现查询的

public Cursor query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)

各参数说明：
table：表名称
colums：列名称数组
selection：条件子句，相当于where
selectionArgs：条件语句的参数数组
groupBy：分组
having：分组条件
orderBy：排序类
limit：分页查询的限制
Cursor：返回值，相当于结果集ResultSet

针对游标（Cursor）也提供了不少方法

方法名称	方法描述
getCount()	总记录条数
isFirst()	判断是否第一条记录
isLast()	判断是否最后一条记录
moveToFirst()	移动到第一条记录
moveToLast()	移动到最后一条记录
move(int offset)	移动到指定的记录
moveToNext()	移动到吓一条记录
moveToPrevious()	移动到上一条记录
getColumnIndex(String columnName)	获得指定列索引的int类型值

实现代码

通过rawQuery实现的带参数查询

下面是完整代码实现方式

方式一

package com.example.demo.datastore.dao;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.example.demo.datastore.db.PersonOpenHelper;
import com.example.demo.datastore.service.PersonService;

public class PersonDao implements PersonService {

private PersonOpenHelper helper = null;
public PersonDao(Context context) {
helper = new PersonOpenHelper(context);
}

@Override
public boolean addPerson(Object[] params) {
boolean flag = false;
//实现对数据库的添加删除和修改查询的功能
SQLiteDatabase database = null;
try {
String sql = "insert into person(name,address,sex) values(?,?,?)";
database = helper.getWritableDatabase();//实现对数据库的写的操作
database.execSQL(sql, params);
flag = true;
} catch (Exception e) {
e.printStackTrace();
}finally{
if(database!=null){
database.close();
}
}
return flag;
}

@Override
public boolean deletePerson(Object[] params) {
boolean flag = false;
SQLiteDatabase database = null;
try {
String sql = "delete from person where id = ? ";
database = helper.getWritableDatabase();
database.execSQL(sql, params);
flag = true;
} catch (Exception e) {
}finally{
if(database!=null){
database.close();
}
}
return flag;
}

@Override
public boolean updatePerson(Object[] params) {
boolean flag = false;
SQLiteDatabase database = null;
try {
String sql = "update person set name = ? ,address = ?, sex = ? where id = ? ";
database = helper.getWritableDatabase();
database.execSQL(sql, params);
flag = true;
} catch (Exception e) {
}finally{
if(database!=null){
database.close();
}
}
return flag;
}

@Override
public Map<String, String> viewPerson(String[] selectionArgs) {
Map<String,String> map = new HashMap<String, String>();
SQLiteDatabase database = null;
try {
String sql = "select * from person where id = ? ";
database = helper.getReadableDatabase();
Cursor cursor = database.rawQuery(sql, selectionArgs);
//获得数据库的列的个数
int colums = cursor.getColumnCount();
while(cursor.moveToNext()){
for(int i=0;i<colums;i++){
String cols_name = cursor.getColumnName(i);
String cols_value = cursor.getString(cursor.getColumnIndex(cols_name));
if(cols_value==null){
cols_value = "";
}
map.put(cols_name, cols_value);
}
}
} catch (Exception e) {
// TODO: handle exception
}finally{
if(database!=null){
database.close();
}
}
return map;
}

@Override
public List<Map<String, String>> listPersonMaps(String[] selectionArgs) {
// TODO Auto-generated method stub
List<Map<String,String>> list = new ArrayList<Map<String,String>>();
String sql = "select * from person ";
SQLiteDatabase database = null;
try {
database = helper.getReadableDatabase();
Cursor cursor = database.rawQuery(sql, selectionArgs);
int colums = cursor.getColumnCount();
while(cursor.moveToNext()){
Map<String,String> map = new HashMap<String, String>();
for(int i=0;i<colums;i++){
String cols_name = cursor.getColumnName(i);
String cols_value = cursor.getString(cursor.getColumnIndex(cols_name));
if(cols_value==null){
cols_value="";
}
map.put(cols_name, cols_value);
}
list.add(map);
}
} catch (Exception e) {
// TODO: handle exception
}finally{
if(database!=null){
database.close();
}
}
return list;
}

}


方式二

package com.example.demo.datastore.dao;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.example.demo.datastore.db.PersonOpenHelper;
import com.example.demo.datastore.service.PersonService2;

public class PersonDao2 implements PersonService2 {

private PersonOpenHelper helper = null;

public PersonDao2(Context context) {
helper = new PersonOpenHelper(context);
}

@Override
public boolean addPerson(ContentValues values) {
boolean flag = false;
SQLiteDatabase database = null;
long id = -1;
try {
database = helper.getWritableDatabase();
id = database.insert("person", null, values);
flag = (id != -1 ? true : false);
} catch (Exception e) {
// TODO: handle exception
} finally {
if (database != null) {
database.close();
}
}
return flag;
}

@Override
public boolean deletePerson(String whereClause, String[] whereArgs) {
boolean flag = false;
SQLiteDatabase database = null;
int count = 0;
try {
database = helper.getWritableDatabase();
count = database.delete("person", whereClause, whereArgs);
flag = (count > 0 ? true : false);
} catch (Exception e) {
} finally {
if (database != null) {
database.close();
}
}
return flag;
}

@Override
public boolean updatePerson(ContentValues values, String whereClause,
String[] whereArgs) {
boolean flag = false;
SQLiteDatabase database = null;
int count = 0;// 影响数据库的行数
try {
database = helper.getWritableDatabase();
count = database.update("person", values, whereClause, whereArgs);
flag = (count > 0 ? true : false);
} catch (Exception e) {
// TODO: handle exception
} finally {
if (database != null) {
database.close();
}
}
return flag;
}

@Override
public Map<String, String> viewPerson(String selection,
String[] selectionArgs) {
// select 返回的列的名称(投影查询) from
SQLiteDatabase database = null;
Cursor cursor = null;
Map<String, String> map = new HashMap<String, String>();
try {
database = helper.getReadableDatabase();
cursor = database.query(true, "person", null, selection,
selectionArgs, null, null, null, null);
int cols_len = cursor.getColumnCount();
while (cursor.moveToNext()) {
for (int i = 0; i < cols_len; i++) {
String cols_name = cursor.getColumnName(i);
String cols_value = cursor.getString(cursor
.getColumnIndex(cols_name));
if (cols_value == null) {
cols_value = "";
}
map.put(cols_name, cols_value);
}
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
if (database != null) {
database.close();
}
}
return map;
}

@Override
public List<Map<String, String>> listPersonMaps(String selection,
String[] selectionArgs) {
// TODO Auto-generated method stub
List<Map<String, String>> list = new ArrayList<Map<String, String>>();
SQLiteDatabase database = null;
Cursor cursor = null;
try {
database = helper.getReadableDatabase();
cursor = database.query(false, "person", null, selection,
selectionArgs, null, null, null, null);
int cols_len = cursor.getColumnCount();
while (cursor.moveToNext()) {
Map<String, String> map = new HashMap<String, String>();
for (int i = 0; i < cols_len; i++) {
String cols_name = cursor.getColumnName(i);
String cols_value = cursor.getString(cursor
.getColumnIndex(cols_name));
if (cols_value == null) {
cols_value = "";
}
map.put(cols_name, cols_value);
}
list.add(map);
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
if (database != null) {
database.close();
}
}
return list;
}

}