SQLite存储对象

前言

sqliteDataBase能存储的数据类型有:
1.NULL:空值。
2.INTEGER:带符号的整型,具体取决有存入数字的范围大小。
3.REAL:浮点数字,存储为8-byte IEEE浮点数。
4.TEXT:字符串文本。
5.BLOB:二进制对象。

下面就来用一个例子讲讲sqlite存储对象。

一.先抛出一个model,类名为Person,代码如下:
package com.example.pei.textdemo.sqlite;

import com.example.pei.textdemo.models.BaseModel;

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/16
 */
public class Person extends BaseModel {

    private String name;
    private String sex;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

这个类很简单,注意的是Person需要实现 Serializable接口,方便序列化,大家如果对以上代码中BaseModel有疑问的话,可以看看我的文章SQLiteDatabase学习(二),这里就不做介绍了

二.写创建数据库的类ObjectOpenHelper

ObjectOpenHelper需要继承SQLiteOpenHelper,然后在创建数据表person的时候,Person会对应表中的data字段,data数据类型为 BLOB,具体代码如下:

package com.example.pei.textdemo.sqlite_object;

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

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/22
 */
public class ObjectOpenHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "save_object.db";//数据库文件名
    private static SQLiteDatabase INSTANCE;
    private Context mContext;

    public SQLiteDatabase getInstance() {
        if (INSTANCE == null) {
            INSTANCE = new ObjectOpenHelper(mContext).getWritableDatabase();
        }
        return INSTANCE;
    }

    public ObjectOpenHelper(Context context) {
        this(context, DB_NAME, null, 1);
        this.mContext=context;
    }

    public ObjectOpenHelper(Context context, String dbName, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, dbName, factory, version);
    }

    //首次创建数据库时调用,一般进行建库建表操作
    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE IF NOT EXISTS person(_id integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n" +
                "                                data BLOB);";
        //创建表
        db.execSQL(createTable);
    }

    //当数据库的版本发生变化的时候会自动执行,禁止人为调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }


}

三.编写数据库的抽象管理类ObjectDBHepler

代码如下:

package com.example.pei.textdemo.sqlite_object;

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

import com.example.pei.textdemo.app.AppContext;

import java.util.List;

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/22
 */
public abstract class ObjectDBHepler {

    protected ObjectOpenHelper mObjectOpenHelper;

    private ObjectOpenHelper getObjectDBHelper(){
        if(mObjectOpenHelper==null){
            mObjectOpenHelper=new ObjectOpenHelper(AppContext.getInstance());
        }
        return mObjectOpenHelper;
    }

    /**获取数据库对象**/
    protected SQLiteDatabase getDateBase(){
        return getObjectDBHelper().getInstance();
    }

    /**关闭数据库**/
    protected void closeDB(){
        SQLiteDatabase db = getDateBase();
        if(db!=null){
            db.close();
        }
    }

    /**
     * 判断表是否存在
     * @param tableName:表名
     * @return
     */
    protected boolean isTableExist(String tableName){
        Cursor cursor = getDateBase().rawQuery("select name from sqlite_master where type='table';", null);
        while(cursor.moveToNext()){
            //遍历出表名
            String name = cursor.getString(0);
            if(name.equals(tableName)){
                return true;
            }
        }
        return false;
    }

    /**查询**/
    protected abstract List<?> checkAll();
    /**添加**/
    protected abstract <T>void insertObject(T t);
    /**删除**/
    protected abstract void delete(Object obj);
    /**更新**/
    protected abstract void update(Object obj);

}

四.实现数据的增删改查类ObjUserHelper,此类需要继承ObjectDBHepler,然后在activity中会调用
package com.example.pei.textdemo.sqlite_object;

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

import com.example.pei.textdemo.sqlite.Person;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/22
 */
public class ObjUserHelper extends ObjectDBHepler{

    private ObjUserHelper() {
    }

    private static class Holder {
        private static ObjUserHelper instance = new ObjUserHelper();
    }

    public static ObjUserHelper getInstance() {
        return ObjUserHelper.Holder.instance;
    }

    @Override
    protected List<?> checkAll() {
        List<Person>list=new ArrayList<>();
        SQLiteDatabase database = getDateBase();
        Cursor cursor = database.rawQuery("select * from person", null);
        if (cursor != null) {
            while (cursor.moveToNext()) {
                byte data[] = cursor.getBlob(cursor.getColumnIndex("data"));
                ByteArrayInputStream arrayInputStream = new ByteArrayInputStream(data);
                try {
                    ObjectInputStream inputStream = new ObjectInputStream(arrayInputStream);
                    Person person = (Person) inputStream.readObject();
                    inputStream.close();
                    arrayInputStream.close();
                    list.add(person);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            cursor.close();
        }
        return list;
    }

    @Override
    protected <T> void insertObject(T t) {
        Person person= (Person) t;
        ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream();
        try {
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(arrayOutputStream);
            objectOutputStream.writeObject(person);
            objectOutputStream.flush();
            byte data[] = arrayOutputStream.toByteArray();
            objectOutputStream.close();
            arrayOutputStream.close();
            SQLiteDatabase database = getDateBase();
            String sql="insert into person(data) values (?)";
            database.execSQL(sql,new Object[]{ data });
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }


    @Override
    protected void delete(Object obj) {

    }

    @Override
    protected void update(Object obj) {

    }
}

五.在MainActivity中的调用
  Person p=new Person();
  p.setAge(25);
  p.setName("展昭");
  p.setSex("nan");

  ObjUserHelper.getInstance().insertObject(p);
  LogUtil.e(SqliteObjectActivity.class,"====save success====");

  List<Person>persons= (List<Person>) ObjUserHelper.getInstance().checkAll();
  if(persons.isEmpty()){
      LogUtil.e(SqliteObjectActivity.class,"=====persons is null=====");
  }else{
     for(Person pt:persons){
        LogUtil.e(SqliteObjectActivity.class,"=====pt=="+pt.objectToString(pt));
     }
   }

最后看看运行的结果:

《SQLite存储对象》 1.png

ok,关于sqlite就讲到这里了,谢谢。

    原文作者:奔跑的佩恩
    原文地址: https://www.jianshu.com/p/6dc28d9ec8cc
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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