什么是关系数据库

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.

基础样例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;    }}

@Database(entities = {OrmUser.class}, version = 1)public abstract class OrmDBDemo extends OrmDatabase {}

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();    }}

<?xml version="1.0" encoding="utf-8"?><DirectionalLayout    xmlns: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