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鸿蒙关系数据库是适合在移动设备上使用的轻量型关系型数据库,速度快,占用空间小.与轻量数据库适合存储少量简单类型数据相反,关系数据库适合存储大量复杂类型的数据.

1. 拷贝数据库相关依赖jar到工程目录下

• 文件：orm_annotations_java.jar和orm_annotations_processor_java.jar
  存放目录样例：d:\program files\huawei\sdk\java\3.0.0.0\build-tools\lib
  
• 拷贝到工程entry目录下libs里
  

2. 修改工程的build.gradle文件
   添加如下行：

annotationprocessor files("./libs/orm_annotations_java.jar", "./libs/orm_annotations_processor_java.jar")

3. 添加数据库对象定义:ormuser.java

@entity(tablename = "ormuser")
public class ormuser extends ormobject {
    @primarykey(autogenerate = true)
    private int id;
    private int userid;
    private string username;
    public int getid() {
        return id;
    }
    public void setid(int id) {
        this.id = id;
    }
    public int getuserid() {
        return userid;
    }
    public void setuserid(int userid) {
        this.userid = userid;
    }
    public string getusername() {
        return username;
    }
    public void setusername(string username) {
        this.username = username;
    }
}

4. 添加数据库操作对象定义:ormdbdemo.java

@database(entities = {ormuser.class}, version = 1)
public abstract class ormdbdemo extends ormdatabase {
}

5. 修改slice代码：mainabilityslice.java

public class mainabilityslice extends abilityslice { 

private ormcontext ormcontext;
@override
public void onstart(intent intent) { 

super.onstart(intent);
super.setuicontent(resourcetable.layout_ability_main);
findcomponentbyid(resourcetable.id_writetext).setclickedlistener(component -> write());
findcomponentbyid(resourcetable.id_readtext).setclickedlistener(component -> read());
findcomponentbyid(resourcetable.id_modifytext).setclickedlistener(component -> modify());
findcomponentbyid(resourcetable.id_deltext).setclickedlistener(component -> del());
initdb();
}
private void initdb() { 

databasehelper databasehelper = new databasehelper(this);
ormcontext = databasehelper.getormcontext("ormdbtest", "ormdbtest.db", ormdbdemo.class);
}
private void write() { 

int userid = 1;
ormuser ormuser = new ormuser();
ormuser.setuserid(userid);
ormuser.setusername("花生皮编程");
ormcontext.insert(ormuser);
ormcontext.flush();
}
private void read() { 

list<ormuser> ormusers = query();
new toastdialog(getcontext()).settext(ormusers.get(0).getusername()).show();
}
private list<ormuser> query() { 

//查询userid = 1的数据
int userid = 1;
ormpredicates ormpredicates = ormcontext.where(ormuser.class).equalto("userid", userid);
return ormcontext.query(ormpredicates);
}
private void modify() { 

//将查询出来的数据值修改后更新到数据库
ormuser ormuser = query().get(0);
if (ormuser == null) { 

return;
}
ormuser.setusername("花生皮編程2");
ormcontext.update(ormuser);
ormcontext.flush();
}
private void del() { 

//将查询出来的第一条数据从数据库中删除
ormuser ormuser = query().get(0);
if (ormuser == null) { 

return;
}
ormcontext.delete(ormuser);
ormcontext.flush();
}
}

6. 对应页面布局文件:

<directionallayout xmlns:ohos="http://schemas.huawei.com/res/ohos" ohos:height="match_parent" ohos:width="match_parent" ohos:alignment="center" ohos:orientation="vertical">
<text ohos:id="$ id:writetext" ohos:height="match_content" ohos:width="match_content" ohos:text="写数据" ohos:text_size="20fp"/>
<text ohos:id="$ id:readtext" ohos:height="match_content" ohos:width="match_content" ohos:text="读数据" ohos:text_size="20fp"/>
<text ohos:id="$ id:modifytext" ohos:height="match_content" ohos:width="match_content" ohos:text="修改数据" ohos:text_size="20fp"/>
<text ohos:id="$ id:deltext" ohos:height="match_content" ohos:width="match_content" ohos:text="删除数据" ohos:text_size="20fp"/>
directionallayout>

ps: 上述代码已包含数据库常见的增删改查功能，代码已优化至最简。

完整源代码

https://gitee.com/hspbc/harmonyos_demos/tree/master/dbdemo

厦门大学计算机专业 | 前华为工程师
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