xUtils3.0的使用(三) 数据库操作

最近才接触xUtils，看了一会才发现已更新3.0的新版本，例子简直少的可怜，还是各种互抄各种转载=。=
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本文主要就单表查询做一番演示（为了解耦做了一点封装）：
这里一共有四步操作：
1.首先，得有个实体类吧（xUtils用注解建表）
2.新建一个DatabaseOpenHelper类，封装初始化操作，提供DbManager.DaoConfig对象（数据库辅助建立类）
3.新建一个与业务数据库操作相关的类，这里就是PersonDB类（具体业务模块实现类）
这个类会把一些常用的数据库操作封装起来
4.在Activity中使用

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1.创建实体类

@Table(name="Person")
public class Person {
    @Column(name = "id",isId = true)
    private int id;
    @Column(name = "name")
    private String name;
    @Column(name = "age")
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    //这里注意，要使用构造器初始化时，必须再提供一个无参构造器
     //我觉得是和注解有关吧
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    //为了测试方便加个toString
}

2.DatabaseOpenHelper类

public class DatabaseOpenHelper {
    private DbManager.DaoConfig daoConfig;
    public DatabaseOpenHelper(String name,int version) {
         daoConfig = new DbManager.DaoConfig()
                .setDbName(name)
                .setDbVersion(version)
                .setDbOpenListener(new DbManager.DbOpenListener() {
                    @Override
                    public void onDbOpened(DbManager db) {
                        db.getDatabase().enableWriteAheadLogging();
                        //开启WAL, 对写入加速提升巨大(作者原话)
                    }
                })
                .setDbUpgradeListener(new DbManager.DbUpgradeListener() {
                    @Override
                    public void onUpgrade(DbManager db, int oldVersion, int newVersion) {
                        //数据库升级操作
                    }
                });
    }
    public DbManager.DaoConfig getDaoConfig(){
        return daoConfig;
    }
}

3.PersonDB类

public class PersonDB {
    public static final String DB_NAME = "person.db";
    //数据库名
    public static final int VERSION = 1;
    //数据库版本号
    private static PersonDB personDB;
    private static DbManager db;
    //接收构造方法初始化的DbManager对象
    private PersonDB(){
        DatabaseOpenHelper databaseOpenHelper = new DatabaseOpenHelper(DB_NAME,VERSION);
        db = x.getDb(databaseOpenHelper.getDaoConfig());
    }
    //构造方法私有化,拿到DbManager对象
    public synchronized static PersonDB getIntance(){
        if (personDB == null){
            personDB = new PersonDB();
        }
        return personDB;
    }
    //获取PersonDB实例

    /****************************************************************************************/
    //写两个测试方法，也就是常用的数据库操作
    public void savePerson(Person person){
        try {
            db.save(person);
            Log.d("xyz","save succeed!");
        } catch (DbException e) {
            Log.d("xyz",e.toString());
        }
    }
    //将Person实例存进数据库
    public List<Person> loadPerson(){
        List<Person> list = null;
        try {
            list = db.selector(Person.class).findAll();
        } catch (DbException e) {
            e.printStackTrace();
        }
        return list;
    }
    //读取所有Person信息
}

4.在Activity中使用

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        PersonDB personDB = PersonDB.getIntance();
        Person person1 = new Person("jay",20);
        Person person2 = new Person("wang",40);
        personDB.savePerson(person1);
        personDB.savePerson(person2);
        //写
        List<Person> list = personDB.loadPerson();
        if (list!=null) {
            for (Person person : list) {
                Log.d("xyz", person.toString());
            }
        }
        //读
    }
}

<!--------16/8/2/19:48更新--------------------------------------------------------------------------------------->
由于对数据库单例不熟，有以下改进写法：
DatabaseOpenHelper类：

public class DatabaseOpenHelper {
    private DbManager.DaoConfig daoConfig;
    private static DbManager db;
    private final String DB_NAME = "mydb";
    private final int VERSION = 1;
    private DatabaseOpenHelper() {
         daoConfig = new DbManager.DaoConfig()
                .setDbName(DB_NAME)
                .setDbVersion(VERSION)
                .setDbOpenListener(new DbManager.DbOpenListener() {
                    @Override
                    public void onDbOpened(DbManager db) {
                        db.getDatabase().enableWriteAheadLogging();
                        //开启WAL, 对写入加速提升巨大(作者原话)
                    }
                })
                .setDbUpgradeListener(new DbManager.DbUpgradeListener() {
                    @Override
                    public void onUpgrade(DbManager db, int oldVersion, int newVersion) {
                        //数据库升级操作
                    }
                });
        db = x.getDb(daoConfig);
    }
    public static DbManager getInstance(){
        if (db == null){
            DatabaseOpenHelper databaseOpenHelper = new DatabaseOpenHelper();
        }
        return db;
    }
}

PersonDB类：

public class PersonDB {
    private DbManager db;
    //接收构造方法初始化的DbManager对象
    public PersonDB(){
        db = DatabaseOpenHelper.getInstance();
    }
    /****************************************************************************************/
    //写两个测试方法
    public void savePerson(Person person){
        try {
            db.save(person);
            Log.d("xyz","save succeed!");
        } catch (DbException e) {
            Log.d("xyz",e.toString());
        }
    }
    //将Person实例存进数据库
    public List<Person> loadPerson(){
        List<Person> list = null;
        try {
            list = db.selector(Person.class).findAll();
        } catch (DbException e) {
            e.printStackTrace();
        }
        return list;
    }
    //读取所有Person信息
}

在Activity中使用：
    

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        PersonDB personDB = new PersonDB();
        Person person1 = new Person("jay",20);
        Person person2 = new Person("wang",40);
        personDB.savePerson(person1);
        personDB.savePerson(person2);
        List<Person> list = personDB.loadPerson();
        if (list!=null) {
            for (Person person : list) {
                Log.d("xyz", person.toString());
            }
        }
    }