上一篇体验了关系型数据库,那一部分API允许我们自由的手写SQL。
这一篇的对象映射数据库是标准的ORM映射类似于Java中的hibernate框架,
将对象映射为表,更改对象就是更改表。
遇到问题
1 在删除和更改时手动创建一个对象传递过去,无法删除或者更改。
2 同一个对象多次添加会失败。
这一个图放上边,因为把注解开关放到了项目的gradle文件中导致我以为这个API不能用
实际上是放到模块的gradle文件中。
这是一个数据库
package com.datang.myapplication.slice;
import ohos.data.orm.OrmDatabase;
import ohos.data.orm.annotation.Database;
import ohos.data.rdb.RdbOpenCallback;
@Database(entities = {User.class}, version = 1)
public class DB1 extends OrmDatabase {
@Override
public int getVersion() {
return 0;
}
@Override
public RdbOpenCallback getHelper() {
return null;
}
}
这是一个表
package com.datang.myapplication.slice;
import ohos.data.orm.OrmObject;
import ohos.data.orm.annotation.Entity;
import ohos.data.orm.annotation.PrimaryKey;
@Entity(tableName = "user")
public class User extends OrmObject {
// 此处将userId设为了自增的主键。注意只有在数据类型为包装类型时,自增主键才能生效。
@PrimaryKey(autoGenerate = true)
private Integer userId;
private String name;
private int age;
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
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 "User{" +
"userId=" + userId +
", name='" + name + '\'' +
", age=" + age +
'}';
}
}
CRUD基本操作
package com.datang.myapplication.slice;
import com.datang.myapplication.ResourceTable;
import ohos.aafwk.ability.AbilitySlice;
import ohos.aafwk.content.Intent;
import ohos.agp.components.Button;
import ohos.data.DatabaseHelper;
import ohos.data.orm.AllChangeToTarget;
import ohos.data.orm.OrmContext;
import ohos.data.orm.OrmObjectObserver;
import ohos.data.orm.OrmPredicates;
import ohos.data.rdb.*;
import ohos.data.resultset.ResultSet;
import ohos.hiviewdfx.HiLog;
import ohos.hiviewdfx.HiLogLabel;
import java.util.List;
//关系型数据库
public class MainAbilitySlice2 extends AbilitySlice {
HiLogLabel label = new HiLogLabel(HiLog.LOG_APP, 0x00201, "MY_TAG");
OrmContext context = null;
@Override
public void onStart(Intent intent) {
super.onStart(intent);
super.setUIContent(ResourceTable.Layout_ability_main2);
initDB();
insert();
select();
delete();
update();
//注册 user 表监听事件 insert update delete 会触发
context.registerEntityObserver("user", (o, a) -> {
HiLog.info(label, "触发回调了》》》》》》》》》》》》》》》》》》");
});
}
@Override
public void onActive() {
super.onActive();
}
public void initDB() {
DatabaseHelper helper = new DatabaseHelper(this);
context = helper.getOrmContext("DB1", "DB1.db", DB1.class);
}
//增加
public void insert() {
Button button = (Button) findComponentById(ResourceTable.Id_add);
button.setClickedListener(e -> {
for (int i = 1; i <= 10; i++) {
//将这个对象添加进去,此外这里如果将User对象放到循环外,则会添加失败抛出异常
//意味着不能对同一个对象做多次添加。就算属性都一样,也要创建多个。不知道是不是
//bug
User user = new User();
user.setName("Zhang" + i);
user.setAge(i);
boolean isSuccessed = context.insert(user);
//没有刷新添加不进去
isSuccessed = context.flush();
HiLog.info(label, "添加是否成功%{public}d,%{public}s", i, isSuccessed);
}
});
}
//查询
public void select() {
Button button2 = (Button) findComponentById(ResourceTable.Id_get);
button2.setClickedListener(e -> {
OrmPredicates query = context.where(User.class);
List<User> users = context.query(query);
users.forEach(c -> {
HiLog.info(label, "查询结果%{public}s", users);
});
});
}
//删除
public void delete() {
Button button3 = (Button) findComponentById(ResourceTable.Id_del);
button3.setClickedListener(e -> {
// 删除数据 User{userId=1, name='Zhang1', age=1}
//直接创建一个 user对象,属性全部设置也不会删除
// User user = new User();
// user.setUserId(1);
// user.setName("Zhang1");
// user.setAge(1);
//User{userId=1, name='Zhang1', age=1}
//从数据库查出来的却可以用,实际上和上边那个创建出来的属性一样
OrmPredicates predicates = context.where(User.class);
predicates.equalTo("userId", 1);
List<User> users = context.query(predicates);
User user = users.get(0);
boolean delete = context.delete(user);
//需要flush
boolean flush = context.flush();
HiLog.info(label, "是否删除%{public}s", flush);
//这种删除方式就类似批量删除了,只给出删除条件,多少都删
OrmPredicates predicates2 = context.where(User.class);
predicates2.equalTo("name", "Zhang2");
int delete2 = context.delete(predicates2);
//并且不用flush
//boolean flush = context.flush();
HiLog.info(label, "是否删除%{public}d", delete2);
});
}
//更改
public void update() {
Button button4 = (Button) findComponentById(ResourceTable.Id_upd);
button4.setClickedListener(e -> {
//同样手动创建的user也无法更改
// User user = new User();
// user.setUserId(1);
// user.setName("李四特");
// user.setAge(33);
//查询出来
OrmPredicates predicates = context.where(User.class);
predicates.equalTo("userId", 1);
List<User> users = context.query(predicates);
User user = users.get(0);
user.setName("李四特");
//更改
boolean update = context.update(user);
//需要flush
boolean flush = context.flush();
HiLog.info(label, "更改成功:%{public}s", update);
//这种方式也是批量更改,更改后的值在 ValuesBucket中存储
OrmPredicates predicates2 = context.where(User.class);
predicates2.equalTo("userId", 2);
ValuesBucket valuesBucket = new ValuesBucket();
valuesBucket.putInteger("age", 31);
valuesBucket.putString("name", "王二麻子");
context.update(predicates2, valuesBucket);
//不需要flush
//boolean flush = context.flush();
HiLog.info(label, "更改成功:%{public}s", update);
});
}
}
作者:顶风少年
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