SQLiteDatabase学习(二)

前言

今天主要讲讲sqlite在android中的创建，存储 和 sqlite的增删改查。

下面以一个例子做讲解

一 创建数据库，需要继承SQLiteOpenHelper

下面是创建user数据库的类DBOpenHelper

package com.example.pei.textdemo.sqlite;

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

/**
 * Title:创建数据库
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/16
 */
public class DBOpenHelper extends SQLiteOpenHelper{

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

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

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

    public DBOpenHelper(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 user(_id integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n" +
                "                                name text,\n" +
                "                                sex text,\n" +
                "                                age integer);";
        //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) {

    }

}

二 提供一个数据库增删改查的抽象类，主要用来统一管理整个数据库涉及到的增删改查

下面是提供增删改查抽象类DBHelper

package com.example.pei.textdemo.sqlite;

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

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

import java.util.List;

/**
 * Title:数据库增删改查帮助类
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/16
 */
public abstract class DBHelper {

    protected DBOpenHelper mDBOpenHelper;

    /**获取数据库对象**/
    protected SQLiteDatabase getDateBase(){
        mDBOpenHelper=new DBOpenHelper(AppContext.getInstance());
        return mDBOpenHelper.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 void insert(Object obj);
    /**删除**/
    protected abstract void delete(Object obj);
    /**更新**/
    protected abstract void update(Object obj);
}

三 提供一个装处理数据的对象

下面是对象person的代码，很简单，就提供了些基本的set，get方法

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;
    }
}

四 Person需要继承的baseModel类

baseModel主要有两个作用：

• 1 实现Serializable接口，方便数据的有序化
• 2 提供 objectToString 方法，作用是将一个对象中所有属性都显示出来，其实就是方便我打印log啦
  下面是 baseModel 代码

package com.example.pei.textdemo.models;


import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/10/30
 */
public class BaseModel implements Serializable{

    /**打印对象属性值**/
    public String objectToString(Object obj){
        List<Map<String,Object>>FiledInfos=getFiledsInfo(obj);
        StringBuffer buffer=new StringBuffer();
        if(!FiledInfos.isEmpty()){
            for(Map<String,Object>map:FiledInfos){
                String tag=map.get("name").toString();
                if(!"$change".equals(tag)&&!"serialVersionUID".equals(tag)){
                    String str=map.get("name")+"="+map.get("value")+"  ";
                    buffer.append(str);
                }
            }
        }else{
            if(obj!=null){
                String className=obj.getClass().getSimpleName();
                buffer.append(className);
            }else{
                buffer.append("objectToString方法调用参数为null");
            }
        }
        return buffer.toString();
    }

    /**
     * 获取属性类型(type)，属性名(name)，属性值(value)的map组成的list
     */
    private List getFiledsInfo(Object obj){
        List<Map<String,Object>>list=new ArrayList();
        if(obj!=null) {
            Field fields[] = obj.getClass().getDeclaredFields();
            String fieldNames[] = new String[fields.length];
            Map mapInfo = null;
            for (int i = 0; i < fields.length; i++) {
                Object o = getFieldValueByName(fields[i].getName(), obj);
                mapInfo = new HashMap();
                mapInfo.put("type", fields[i].getType().toString());
                mapInfo.put("name", fields[i].getName());
                mapInfo.put("value", getFieldValueByName(fields[i].getName(), obj));
                list.add(mapInfo);
            }
        }
        return list;
    }

    /**
     * 根据属性名获取属性值 
     */
    private Object getFieldValueByName(String fieldName,Object obj){
        Object value=null;
        try {
            String firstLetter=fieldName.substring(0,1).toUpperCase();
            String getter="get" +firstLetter+fieldName.substring(1);
            Method method=obj.getClass().getMethod(getter,new Class[] {});
            value = method.invoke(obj, new Object[] {});
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
        return value;
    }

    /**
     * 获取属性名数组
     */
    private String[] getFiledName(Object obj){
        Field fields[]=obj.getClass().getDeclaredFields();
        String fieldNames[]=new String[fields.length];
        for(int i=0;i<fields.length;i++){
            fieldNames[i]=fields[i].getName();
        }
        return fieldNames;
    }

    /***
     * 获取对象的所有属性值，返回一个对象数组 
     */
    private Object[] getFiledValues(Object obj){
        String fieldNames[]=this.getFiledName(obj);
        Object value[]=new Object[fieldNames.length];
        for(int i=0;i<fieldNames.length;i++){
            value[i]=this.getFieldValueByName(fieldNames[i],obj);
        }
        return value;
    }

}

五 提供具体的增删改查类UserDBHelper

此类需要继承抽象类DBHelper，在activity中涉及到增删改查时，基本是调用这个类中的方法

package com.example.pei.textdemo.sqlite;

import android.database.Cursor;

import java.util.ArrayList;
import java.util.List;

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

    private UserDBHelper() {
    }

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

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

    @Override
    protected List<Person> checkAll() {
            List<Person> list = new ArrayList<>();
            //COLLATE NOCASE 忽略大小写查询
//            Cursor cursor = getDateBase().rawQuery("select * from T_cpz where isqy='True' COLLATE NOCASE;", null);
            Cursor cursor = getDateBase().rawQuery("select * from user", null);
            while (cursor.moveToNext()) {
                String name = cursor.getString(cursor.getColumnIndex("name"));
                String sex = cursor.getString(cursor.getColumnIndex("sex"));
                int age=cursor.getInt(cursor.getColumnIndex("age"));

                Person person=new Person();
                person.setName(name);
                person.setSex(sex);
                person.setAge(age);
                list.add(person);
            }
            cursor.close();
        return list;
    }

    @Override
    protected void insert(Object obj){
        Person person= (Person) obj;
        String sql="INSERT INTO user(name,sex,age) VALUES('"+ person.getName()+"','"+ person.getSex()+"','"+ person.getAge()+"');";
        getDateBase().execSQL(sql);
    }

    @Override
    protected void delete(Object obj) {
        Person person = (Person) obj;
        String sql = "DELETE FROM user WHERE name='" + person.getName() + "';";
        getDateBase().execSQL(sql);
    }

    @Override
    protected void update(Object obj) {
        Person person = (Person) obj;
        String sql="UPDATE user SET age="+person.getAge()+" WHERE name='"+person.getName()+"';";
        getDateBase().execSQL(sql);
    }


}

六 下面看看在activity中涉及到的具体数据的处理

此处只显示一些增删改查的代码，仅做范例

//                //添加
//                Person person=new Person();
//                person.setName("大和");
//                person.setSex("男");
//                person.setAge(28);
//                Person person1=new Person();
//                person1.setName("红豆");
//                person1.setSex("女");
//                person1.setAge(26);
//                UserDBHelper.getInstance().insert(person);
//                UserDBHelper.getInstance().insert(person1);
//                List<Person> persons=UserDBHelper.getInstance().checkAll();
//                for(Person p:persons){
//                    LogUtil.e(SqliteActivity.class,"===p="+p.objectToString(p));
//                }

//                //更新
//                Person updatePerson = new Person();
//                updatePerson.setName("大和");
//                updatePerson.setSex("男");
//                updatePerson.setAge(30);
//                UserDBHelper.getInstance().update(updatePerson);
//                List<Person> persons = UserDBHelper.getInstance().checkAll();
//                for (Person p : persons) {
//                    LogUtil.e(SqliteActivity.class, "===p=" + p.objectToString(p));
//                }

//                //删除
//                Person deletePerson = new Person();
//                deletePerson.setName("大和");
//                deletePerson.setSex("男");
//                deletePerson.setAge(30);
//                UserDBHelper.getInstance().delete(deletePerson);
//                List<Person> persons = UserDBHelper.getInstance().checkAll();
//                for (Person p : persons) {
//                    LogUtil.e(SqliteActivity.class, "===p=" + p.objectToString(p));
//                }

                //查询所有
                List<Person> persons = UserDBHelper.getInstance().checkAll();
                for (Person p : persons) {
                    LogUtil.e(SqliteActivity.class, "===p=" + p.objectToString(p));
                }

ok，今天只是对android数据库的一个简单讲解了，具体到项目中运用的时候，我们还需要对以上 helper类做针对性的修改

谢谢诶！