如何使用 Room 创建多个表？
How can I create several tables, using Room?
我有一些问题。在我的应用程序中，我使用名为“Templates”的 Sqlite 数据库，我想创建几个 table，例如 peopleTemplates、animalsTemplates，它们由列 id、description、image_link。还有特别的tablefavourites，我会把用户喜欢的模板都加进去。我将使用 RoomDatabase。这是我的 TemplatesClass:
@Entity(tableName = "my_templates")
public class MyTemplate implements Serializable {
@PrimaryKey(autoGenerate = true)
public int id;
@ColumnInfo(name = "description")
public String titleTemplate;
@ColumnInfo(name = "image_link")
public String imageLink;
public String getTitleTemplate() {
return titleTemplate;
}
public void setTitleTemplate(String titleTemplate) {
this.titleTemplate = titleTemplate;
}
public String getImageLink() {
return imageLink;
}
public void setDrawableID(String imageLink) {
this.imageLink = imageLink;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public MyTemplate(String titleTemplate, String imageLink){
this.titleTemplate = titleTemplate;
this.imageLink = imageLink;
}
public MyTemplate(){}
}
我的数据库类：
@Database(entities = {MyTemplate.class}, version = 1, exportSchema = false)
public abstract class RoomDB extends RoomDatabase {
private static RoomDB database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDB getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDB.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract TemplateDao templateDao();
}
还有我的道：
@Dao
public interface TemplateDao {
@Insert(onConflict = REPLACE)
void insert(MyTemplate myTemplate);
@Delete
void delete(MyTemplate myTemplate);
@Delete
void reset(ArrayList<MyTemplate> myTemplates);
@Query("UPDATE my_templates SET description = :sDescription WHERE id = :sID")
void update(int sID, String sDescription);
@Query("SELECT * FROM my_templates")
List<MyTemplate> getAll();
}
使用 @Entity 创建额外的 table 实体。
创建适当的 Dao（根据您的选择全部合一或每个实体一个）
修改@Database (RoomDB class) entities = 以将其他实体 class 包含在实体数组中。如果使用多个 Dao，则添加用于检索 Dao 的抽象方法（即类似于 public abstract TemplateDao templateDao();）。
至少对于模板 table 来说，如果您添加一个表示类型（人、动物等）的列，那么单个 table 似乎就足以满足所有模板
示例 1 - 附加 tables
1. 创建新实体
@Entity(tableName = "people_templates")
public class PeopleTemplate implements Serializable {
@PrimaryKey(autoGenerate = true)
public long id; //<<<<<<<<< Should really be long not int
@ColumnInfo(name = "description")
public String titleTemplate;
@ColumnInfo(name = "image_link")
public String imageLink;
public String getTitleTemplate() {
return titleTemplate;
}
public void setTitleTemplate(String titleTemplate) {
this.titleTemplate = titleTemplate;
}
public String getImageLink() {
return imageLink;
}
public void setDrawableID(String imageLink) {
this.imageLink = imageLink;
}
public long getId() { // long
return id;
}
public void setId(long id) { // long
this.id = id;
}
public PeopleTemplate(String titleTemplate, String imageLink){
this.titleTemplate = titleTemplate;
this.imageLink = imageLink;
}
public PeopleTemplate(){}
}
- 请注意，id 列的 int 已更改为 long。理论上 id 可以很长，Room 在使用 @Insert 时期望 return 长。
2.修道
@Dao
public interface TemplateDao {
@Insert(onConflict = REPLACE)
void insert(MyTemplate myTemplate);
@Insert(onConflict = REPLACE)
long insert(PeopleTemplate peopleTemplate); // long will hold the id of the inserted row
@Insert(onConflict = REPLACE)
long[] insert(PeopleTemplate...peopleTemplates); // allows many (e.g. ArrayList to be added), returns long[] of id's inserted
@Delete
void delete(MyTemplate myTemplate);
@Delete
int delete(PeopleTemplate...peopleTemplate); // delete 1 or many, returns number deleted
@Delete
void reset(ArrayList<MyTemplate> myTemplates);
@Query("UPDATE my_templates SET description = :sDescription WHERE id = :sID")
void update(int sID, String sDescription);
@Query("UPDATE people_templates SET description = :sDescription WHERE id = :sID")
int update(long sID, String sDescription); // returns number of updates
@Query("SELECT * FROM my_templates")
List<MyTemplate> getAll();
@Query("SELECT * FROM people_templates")
List<PeopleTemplate> getAllPeopleTemplates();
}
- 注意评论
3.合并到@Databaseclass
//@Database(entities = {MyTemplate.class}, version = 1, exportSchema = false) <<<<<<<<<< WAS THIS
@Database(entities = {MyTemplate.class,PeopleTemplate.class}, version = 1, exportSchema = false) //<<<<<<<<<< CHANGED
public abstract class RoomDB extends RoomDatabase {
private static RoomDB database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDB getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDB.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract TemplateDao templateDao();
}
示例 2 - 单个 Table
这是一个适用于多种模板类型的单一模板的工作示例table
SingleTemplate实体
@Entity(tableName = "templates")
public class SingleTemplate implements Serializable {
public static final int MY_TEMPLATE = 0;
public static final int PEOPLE_TEMPLATE = 1;
public static final int ANIMAL_TEMPLATE = 2;
/* suggest not using AUTOGENERATE as it has overheads
using Long and passing null has the same result without overheads
*/
@PrimaryKey
Long id;
@ColumnInfo(name = "description")
String title;
@ColumnInfo(name = "image_link")
String imageLink;
@ColumnInfo(name = "template_type")
int templateType;
public SingleTemplate(){}
// Use @Ignore to suppress warning "There are multiple good constructors and Room will pick the no-arg constructor...."
@Ignore
public SingleTemplate(String title, String imageLink, int templateType) {
this.title = title;
this.imageLink = imageLink;
this.templateType = templateType;
}
/* Method to allow conversion of type to a user readable String */
public static String getType(int templateType) {
switch (templateType) {
case MY_TEMPLATE:
return "MY";
case PEOPLE_TEMPLATE:
return "PEOPLE";
case ANIMAL_TEMPLATE:
return "ANIMAL";
default:
return "UNKNOWN";
}
}
}
The Dao SingleTemplateDao
@Dao
interface SingleTemplateDao {
@Insert(onConflict = REPLACE)
long insert(SingleTemplate singleTemplate);
@Insert(onConflict = REPLACE)
long[] insert(SingleTemplate...singleTemplates);
@Update
int update(SingleTemplate...singleTemplate);
@Query("SELECT * FROM templates WHERE template_type IN (:arrayOfTypes)")
List<SingleTemplate> getTemplatesByTypes(int[] arrayOfTypes);
}
@Database class RoomDBSingleTemplate
@Database(entities = {SingleTemplate.class}, version = 1, exportSchema = false) //<<<<<<<<<< CHANGED
public abstract class RoomDBSingleTemplate extends RoomDatabase {
private static RoomDBSingleTemplate database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDBSingleTemplate getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDBSingleTemplate.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract SingleTemplateDao getSingleTemplateDao();
}
Invoking/Demo MainActivity
中的代码
public class MainActivity extends AppCompatActivity {
RoomDBSingleTemplate db;
SingleTemplateDao dao;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = RoomDBSingleTemplate.getInstance(this);
dao = db.getSingleTemplateDao();
// Add one of each type individually
long id = dao.insert(new SingleTemplate("Template1","Link1",SingleTemplate.MY_TEMPLATE));
dao.insert(new SingleTemplate("Template2","Link2", ANIMAL_TEMPLATE));
dao.insert(new SingleTemplate("Template3","Link3",SingleTemplate.PEOPLE_TEMPLATE));
// Add an unknown type
dao.insert(new SingleTemplate("Template4","LINK4",99999));
// Add many templates type determined according to iteration
int limit = 10;
SingleTemplate[] stList = new SingleTemplate[limit];
for(int i=0; i < limit; i++) {
stList[i] = new SingleTemplate(
"Template" + (i+100),
"Link" + (i+100),
i % 3
);
}
dao.insert(stList);
// Get just Animal templates and update the Link by prefixing with ANIMAL
List<SingleTemplate> animalTemplates = dao.getTemplatesByTypes(new int[]{ANIMAL_TEMPLATE});
stList = new SingleTemplate[animalTemplates.size()];
int i=0;
for (SingleTemplate s: animalTemplates) {
s.imageLink = "ANIMAL" + s.imageLink;
stList[i++] = s;
}
dao.update(stList);
// Get all known types and output to the log
List<SingleTemplate> allTemplates = dao.getTemplatesByTypes(new int[]{MY_TEMPLATE,ANIMAL_TEMPLATE,PEOPLE_TEMPLATE});
for(SingleTemplate s: allTemplates) {
Log.d("TEMPLATEINFO",
"Title is " + s.title +
" Link is " + s.imageLink +
" Type is " + SingleTemplate.getType(s.templateType) +
" ID is " + s.id
);
}
}
}
结果 - 在日志中输出。
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template1 Link is Link1 Type is MY ID is 1
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template2 Link is ANIMALLink2 Type is ANIMAL ID is 2
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template3 Link is Link3 Type is PEOPLE ID is 3
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template100 Link is Link100 Type is MY ID is 5
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template101 Link is Link101 Type is PEOPLE ID is 6
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template102 Link is ANIMALLink102 Type is ANIMAL ID is 7
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template103 Link is Link103 Type is MY ID is 8
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template104 Link is Link104 Type is PEOPLE ID is 9
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template105 Link is ANIMALLink105 Type is ANIMAL ID is 10
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template106 Link is Link106 Type is MY ID is 11
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template107 Link is Link107 Type is PEOPLE ID is 12
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template108 Link is ANIMALLink108 Type is ANIMAL ID is 13
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template109 Link is Link109 Type is MY ID is 14
可见
- 已添加 14 行（最后一个 ID 是 14）
- 所有类型为 ANIMAL 的行都已更新 link
- 输出中省略了 UNKNOWN 行（ID 为 4 的 Template4）
更进一步
你说：-
Also there will be special table favourites, I will add there all templates user likes. I am going to use RoomDatabase.
假设用户有多个用户（如果只有 1 个用户也无妨，但如果只有 1 个用户则不需要那么复杂）。
您可能有一个用户 table，例如 :-
@Entity(tableName = "user")
public class User {
@PrimaryKey
Long id;
String userName;
String userEmail;
String userPassword;
public User(){};
@Ignore
public User(String userName, String userEmail, String userPassword) {
this.userName = userName;
this.userEmail = userEmail;
this.userPassword = userPassword;
}
}
link 用户使用他们最喜欢的模板并允许用户使用其他用户使用的模板，则需要 many-many 关系。因此，收藏夹 table 可以是用户和他们喜欢的模板之间的映射。要映射，您需要的只是用户的唯一标识符以及模板的唯一标识符（例如，每个模板的 id 列）。因此，收藏夹 table 可能是：-
/*
Mapping Table for many-many relationship between users and templates
*/
@Entity(
tableName = "favourite",
foreignKeys = {
@ForeignKey(
entity = User.class,
parentColumns = {"id"},
childColumns = {"userId"},
onDelete = CASCADE,
onUpdate = CASCADE
),
@ForeignKey(
entity = SingleTemplate.class,
parentColumns = {"id"},
childColumns = {"templateId"},
onDelete = CASCADE,
onUpdate = CASCADE
)
},
/* composite Primary Key */
primaryKeys = {"userId","templateId"},
indices = {@Index("templateId")}
)
public class Favourites {
long userId;
long templateId;
public Favourites(){}
@Ignore
public Favourites(long userId,long templateId) {
this.userId = userId;
this.templateId = templateId;
}
}
- 这种 table 有很多术语，例如关联 table、引用 table、映射 table ....
- ForeignKey 定义定义了 managing/asserting 参照完整性的规则，它们不是必需的，但它们很有用
- 它们可以防止添加孤儿 children。也就是说，如果尝试在相应 parent 中不存在列值的行中添加行，则会发生外键冲突（参见 Dao）。
- onDelete = CASCADE 将级联删除 parent，以便删除 child 中引用 parent 的所有行。
- onUpdate 类似，但它只会导致在 children 中更改引用的列，并且仅当引用的列发生更改时（这种情况很少发生）。
- 有两个外键定义，一个用于 reference/relationship 到用户 table，另一个用于 refrence/relationship 到 SingleTemplates table。
- templateId 列上的索引不是必需的，但如果省略 Room 会发出警告。
在此阶段可以添加用于插入和检索用户和收藏夹的 Dao。然而，检索收藏夹并不是用户友好的，它们只是没有什么意义的数字。例如
- 1,13 确实意味着 ID 为 1 的用户对 ID 为 13 的模板具有 link ....
因此，您可能希望获取用户详细信息以及模板详细信息。 Room 使这很容易做到你创建一个 POJO class （不是实体），你 Embed 一个实体然后定义一个与另一个class的关系 （嵌入用户与模板)。但是，由于映射 table 在您 之间（仅嵌入和关系满足 one-many 关系） 那么您需要一个 Association 定义了三个 tables.
之间的 Junction
这样一个 suitable POJO 可以是 UserWithFavourites:-
public class UserWithFavourites {
@Embedded
User user; /* One User */
@Relation(entity = SingleTemplate.class, parentColumn = "id",entityColumn = "id",
associateBy = @Junction(value = Favourites.class,parentColumn = "userId",entityColumn = "templateId"))
List<SingleTemplate> singleTemplateList; /* A list of Templates for the User */
}
因此需要 Dao 来检索（查询）数据库。所以 SingleTemplateDao 现在可以是 :-
@Dao
interface SingleTemplateDao {
@Insert(onConflict = REPLACE)
long insert(SingleTemplate singleTemplate);
@Insert(onConflict = REPLACE)
long[] insert(SingleTemplate...singleTemplates);
@Insert(onConflict = REPLACE)
long[] insert(User...users);
@Insert(onConflict = IGNORE)
long[] insert(Favourites...favourites);
@Update
int update(SingleTemplate...singleTemplate);
@Query("SELECT * FROM templates WHERE template_type IN (:arrayOfTypes)")
List<SingleTemplate> getTemplatesByTypes(int[] arrayOfTypes);
@Query("SELECT * FROM user")
List<User> getAllUsers();
@Query("SELECT * FROM user WHERE id=:userId")
User getUserById(long userId);
@Query("SELECT * FROM User")
List<UserWithFavourites> getAllUsersWithFavourites();
}
示例 3
请注意，上面的 insert/updating 和提取代码已移至方法 na编辑示例 2。已创建新方法 example3 来演示添加用户和收藏夹 table，因此 activity 代码现在为：-
public class MainActivity 扩展 AppCompatActivity {
RoomDBSingleTemplate db;
SingleTemplateDao dao;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = RoomDBSingleTemplate.getInstance(this);
dao = db.getSingleTemplateDao();
example2();
example3();
}
private void example3() {
/* Add some Users */
dao.insert(new User("Fred","Fred@email.com","password"), /*ID will be 1 */
new User("Mary","Mary@email.com","password"), /* ID will be 2 */
new User("Sarah","Sarah@email.com","password") /* ID will be 3 */);
/* Using the existing templates map/associate/relate users to templates */
dao.insert(new Favourites(1,1),
new Favourites(1,3),
new Favourites(1,4) /* UNKNOWN TYPE */,
new Favourites(1,10),
new Favourites(2,5),
new Favourites(2,6),
new Favourites(2,7),
new Favourites(2,8),
new Favourites(3,9),
new Favourites(3,11),
new Favourites(3,12),
new Favourites(3,13),
new Favourites(3,14));
/* extract all users with thier templates and then output the results to the log */
List<UserWithFavourites> userWithFavourites = dao.getAllUsersWithFavourites();
for (UserWithFavourites uwf: userWithFavourites) {
Log.d("FAVOURITESINFO",
"User is " + uwf.user.userName +
" email is " + uwf.user.userEmail +
" password is " + uwf.user.userPassword +
" USERID = " + uwf.user.id +
" # of Templates = " + uwf.singleTemplateList.size()
);
for (SingleTemplate st: uwf.singleTemplateList) {
Log.d("FAVOURITESINFO","Template is " + st.title + " Link is " + st.imageLink + " Type is " + getType(st.templateType) + " ID is " + st.id);
}
}
}
private void example2() {
// Add one of each type individually
long id = dao.insert(new SingleTemplate("Template1","Link1",SingleTemplate.MY_TEMPLATE));
dao.insert(new SingleTemplate("Template2","Link2", ANIMAL_TEMPLATE));
dao.insert(new SingleTemplate("Template3","Link3",SingleTemplate.PEOPLE_TEMPLATE));
// Add an unknown type
dao.insert(new SingleTemplate("Template4","LINK4",99999));
// Add many templates type determined according to iteration
int limit = 10;
SingleTemplate[] stList = new SingleTemplate[limit];
for(int i=0; i < limit; i++) {
stList[i] = new SingleTemplate(
"Template" + (i+100),
"Link" + (i+100),
i % 3
);
}
dao.insert(stList);
// Get just Animal templates and update the Link by prefixing with ANIMAL
List<SingleTemplate> animalTemplates = dao.getTemplatesByTypes(new int[]{ANIMAL_TEMPLATE});
stList = new SingleTemplate[animalTemplates.size()];
int i=0;
for (SingleTemplate s: animalTemplates) {
s.imageLink = "ANIMAL" + s.imageLink;
stList[i++] = s;
}
dao.update(stList);
// Get all known types and output to the log
List<SingleTemplate> allTemplates = dao.getTemplatesByTypes(new int[]{MY_TEMPLATE,ANIMAL_TEMPLATE,PEOPLE_TEMPLATE});
for(SingleTemplate s: allTemplates) {
Log.d("TEMPLATEINFO",
"Title is " + s.title +
" Link is " + s.imageLink +
" Type is " + SingleTemplate.getType(s.templateType) +
" ID is " + s.id
);
}
}
}
示例3结果当运行（第一次）日志包括：-
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template1 Link is Link1 Type is MY ID is 1
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template3 Link is Link3 Type is PEOPLE ID is 3
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template4 Link is LINK4 Type is UNKNOWN ID is 4
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template105 Link is ANIMALANIMALLink105 Type is ANIMAL ID is 10
2021-06-09 11:50:11.477 D/FAVOURITESINFO: User is Mary email is Mary@email.com password is password USERID = 2 # of Templates = 4
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template100 Link is Link100 Type is MY ID is 5
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template101 Link is Link101 Type is PEOPLE ID is 6
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template102 Link is ANIMALANIMALLink102 Type is ANIMAL ID is 7
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template103 Link is Link103 Type is MY ID is 8
2021-06-09 11:50:11.477 D/FAVOURITESINFO: User is Sarah email is Sarah@email.com password is password USERID = 3 # of Templates = 5
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template104 Link is Link104 Type is PEOPLE ID is 9
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template106 Link is Link106 Type is MY ID is 11
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template107 Link is Link107 Type is PEOPLE ID is 12
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template108 Link is ANIMALANIMALLink108 Type is ANIMAL ID is 13
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template109 Link is Link109 Type is MY ID is 14
我有一些问题。在我的应用程序中，我使用名为“Templates”的 Sqlite 数据库，我想创建几个 table，例如 peopleTemplates、animalsTemplates，它们由列 id、description、image_link。还有特别的tablefavourites，我会把用户喜欢的模板都加进去。我将使用 RoomDatabase。这是我的 TemplatesClass:
@Entity(tableName = "my_templates")
public class MyTemplate implements Serializable {
@PrimaryKey(autoGenerate = true)
public int id;
@ColumnInfo(name = "description")
public String titleTemplate;
@ColumnInfo(name = "image_link")
public String imageLink;
public String getTitleTemplate() {
return titleTemplate;
}
public void setTitleTemplate(String titleTemplate) {
this.titleTemplate = titleTemplate;
}
public String getImageLink() {
return imageLink;
}
public void setDrawableID(String imageLink) {
this.imageLink = imageLink;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public MyTemplate(String titleTemplate, String imageLink){
this.titleTemplate = titleTemplate;
this.imageLink = imageLink;
}
public MyTemplate(){}
}
我的数据库类：
@Database(entities = {MyTemplate.class}, version = 1, exportSchema = false)
public abstract class RoomDB extends RoomDatabase {
private static RoomDB database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDB getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDB.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract TemplateDao templateDao();
}
还有我的道：
@Dao
public interface TemplateDao {
@Insert(onConflict = REPLACE)
void insert(MyTemplate myTemplate);
@Delete
void delete(MyTemplate myTemplate);
@Delete
void reset(ArrayList<MyTemplate> myTemplates);
@Query("UPDATE my_templates SET description = :sDescription WHERE id = :sID")
void update(int sID, String sDescription);
@Query("SELECT * FROM my_templates")
List<MyTemplate> getAll();
}
使用
@Entity创建额外的 table 实体。创建适当的 Dao（根据您的选择全部合一或每个实体一个）
修改@Database (RoomDB class)
entities =以将其他实体 class 包含在实体数组中。如果使用多个 Dao，则添加用于检索 Dao 的抽象方法（即类似于public abstract TemplateDao templateDao();）。
至少对于模板 table 来说，如果您添加一个表示类型（人、动物等）的列，那么单个 table 似乎就足以满足所有模板
示例 1 - 附加 tables
1. 创建新实体
@Entity(tableName = "people_templates")
public class PeopleTemplate implements Serializable {
@PrimaryKey(autoGenerate = true)
public long id; //<<<<<<<<< Should really be long not int
@ColumnInfo(name = "description")
public String titleTemplate;
@ColumnInfo(name = "image_link")
public String imageLink;
public String getTitleTemplate() {
return titleTemplate;
}
public void setTitleTemplate(String titleTemplate) {
this.titleTemplate = titleTemplate;
}
public String getImageLink() {
return imageLink;
}
public void setDrawableID(String imageLink) {
this.imageLink = imageLink;
}
public long getId() { // long
return id;
}
public void setId(long id) { // long
this.id = id;
}
public PeopleTemplate(String titleTemplate, String imageLink){
this.titleTemplate = titleTemplate;
this.imageLink = imageLink;
}
public PeopleTemplate(){}
}
- 请注意，id 列的 int 已更改为 long。理论上 id 可以很长，Room 在使用 @Insert 时期望 return 长。
2.修道
@Dao
public interface TemplateDao {
@Insert(onConflict = REPLACE)
void insert(MyTemplate myTemplate);
@Insert(onConflict = REPLACE)
long insert(PeopleTemplate peopleTemplate); // long will hold the id of the inserted row
@Insert(onConflict = REPLACE)
long[] insert(PeopleTemplate...peopleTemplates); // allows many (e.g. ArrayList to be added), returns long[] of id's inserted
@Delete
void delete(MyTemplate myTemplate);
@Delete
int delete(PeopleTemplate...peopleTemplate); // delete 1 or many, returns number deleted
@Delete
void reset(ArrayList<MyTemplate> myTemplates);
@Query("UPDATE my_templates SET description = :sDescription WHERE id = :sID")
void update(int sID, String sDescription);
@Query("UPDATE people_templates SET description = :sDescription WHERE id = :sID")
int update(long sID, String sDescription); // returns number of updates
@Query("SELECT * FROM my_templates")
List<MyTemplate> getAll();
@Query("SELECT * FROM people_templates")
List<PeopleTemplate> getAllPeopleTemplates();
}
- 注意评论
3.合并到@Databaseclass
//@Database(entities = {MyTemplate.class}, version = 1, exportSchema = false) <<<<<<<<<< WAS THIS
@Database(entities = {MyTemplate.class,PeopleTemplate.class}, version = 1, exportSchema = false) //<<<<<<<<<< CHANGED
public abstract class RoomDB extends RoomDatabase {
private static RoomDB database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDB getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDB.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract TemplateDao templateDao();
}
示例 2 - 单个 Table
这是一个适用于多种模板类型的单一模板的工作示例table
SingleTemplate实体
@Entity(tableName = "templates")
public class SingleTemplate implements Serializable {
public static final int MY_TEMPLATE = 0;
public static final int PEOPLE_TEMPLATE = 1;
public static final int ANIMAL_TEMPLATE = 2;
/* suggest not using AUTOGENERATE as it has overheads
using Long and passing null has the same result without overheads
*/
@PrimaryKey
Long id;
@ColumnInfo(name = "description")
String title;
@ColumnInfo(name = "image_link")
String imageLink;
@ColumnInfo(name = "template_type")
int templateType;
public SingleTemplate(){}
// Use @Ignore to suppress warning "There are multiple good constructors and Room will pick the no-arg constructor...."
@Ignore
public SingleTemplate(String title, String imageLink, int templateType) {
this.title = title;
this.imageLink = imageLink;
this.templateType = templateType;
}
/* Method to allow conversion of type to a user readable String */
public static String getType(int templateType) {
switch (templateType) {
case MY_TEMPLATE:
return "MY";
case PEOPLE_TEMPLATE:
return "PEOPLE";
case ANIMAL_TEMPLATE:
return "ANIMAL";
default:
return "UNKNOWN";
}
}
}
The Dao SingleTemplateDao
@Dao
interface SingleTemplateDao {
@Insert(onConflict = REPLACE)
long insert(SingleTemplate singleTemplate);
@Insert(onConflict = REPLACE)
long[] insert(SingleTemplate...singleTemplates);
@Update
int update(SingleTemplate...singleTemplate);
@Query("SELECT * FROM templates WHERE template_type IN (:arrayOfTypes)")
List<SingleTemplate> getTemplatesByTypes(int[] arrayOfTypes);
}
@Database class RoomDBSingleTemplate
@Database(entities = {SingleTemplate.class}, version = 1, exportSchema = false) //<<<<<<<<<< CHANGED
public abstract class RoomDBSingleTemplate extends RoomDatabase {
private static RoomDBSingleTemplate database;
private final static String DATABASE_NAME = "Templates";
public synchronized static RoomDBSingleTemplate getInstance(Context context){
if(database == null){
database = Room.databaseBuilder(context.getApplicationContext(),
RoomDBSingleTemplate.class, DATABASE_NAME)
.allowMainThreadQueries()
.fallbackToDestructiveMigration()
.build();
}
return database;
}
public abstract SingleTemplateDao getSingleTemplateDao();
}
Invoking/Demo MainActivity
中的代码public class MainActivity extends AppCompatActivity {
RoomDBSingleTemplate db;
SingleTemplateDao dao;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = RoomDBSingleTemplate.getInstance(this);
dao = db.getSingleTemplateDao();
// Add one of each type individually
long id = dao.insert(new SingleTemplate("Template1","Link1",SingleTemplate.MY_TEMPLATE));
dao.insert(new SingleTemplate("Template2","Link2", ANIMAL_TEMPLATE));
dao.insert(new SingleTemplate("Template3","Link3",SingleTemplate.PEOPLE_TEMPLATE));
// Add an unknown type
dao.insert(new SingleTemplate("Template4","LINK4",99999));
// Add many templates type determined according to iteration
int limit = 10;
SingleTemplate[] stList = new SingleTemplate[limit];
for(int i=0; i < limit; i++) {
stList[i] = new SingleTemplate(
"Template" + (i+100),
"Link" + (i+100),
i % 3
);
}
dao.insert(stList);
// Get just Animal templates and update the Link by prefixing with ANIMAL
List<SingleTemplate> animalTemplates = dao.getTemplatesByTypes(new int[]{ANIMAL_TEMPLATE});
stList = new SingleTemplate[animalTemplates.size()];
int i=0;
for (SingleTemplate s: animalTemplates) {
s.imageLink = "ANIMAL" + s.imageLink;
stList[i++] = s;
}
dao.update(stList);
// Get all known types and output to the log
List<SingleTemplate> allTemplates = dao.getTemplatesByTypes(new int[]{MY_TEMPLATE,ANIMAL_TEMPLATE,PEOPLE_TEMPLATE});
for(SingleTemplate s: allTemplates) {
Log.d("TEMPLATEINFO",
"Title is " + s.title +
" Link is " + s.imageLink +
" Type is " + SingleTemplate.getType(s.templateType) +
" ID is " + s.id
);
}
}
}
结果 - 在日志中输出。
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template1 Link is Link1 Type is MY ID is 1
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template2 Link is ANIMALLink2 Type is ANIMAL ID is 2
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template3 Link is Link3 Type is PEOPLE ID is 3
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template100 Link is Link100 Type is MY ID is 5
2021-06-09 07:44:18.163 D/TEMPLATEINFO: Title is Template101 Link is Link101 Type is PEOPLE ID is 6
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template102 Link is ANIMALLink102 Type is ANIMAL ID is 7
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template103 Link is Link103 Type is MY ID is 8
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template104 Link is Link104 Type is PEOPLE ID is 9
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template105 Link is ANIMALLink105 Type is ANIMAL ID is 10
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template106 Link is Link106 Type is MY ID is 11
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template107 Link is Link107 Type is PEOPLE ID is 12
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template108 Link is ANIMALLink108 Type is ANIMAL ID is 13
2021-06-09 07:44:18.164 D/TEMPLATEINFO: Title is Template109 Link is Link109 Type is MY ID is 14
可见
- 已添加 14 行（最后一个 ID 是 14）
- 所有类型为 ANIMAL 的行都已更新 link
- 输出中省略了 UNKNOWN 行（ID 为 4 的 Template4）
更进一步
你说：-
Also there will be special table favourites, I will add there all templates user likes. I am going to use RoomDatabase.
假设用户有多个用户（如果只有 1 个用户也无妨，但如果只有 1 个用户则不需要那么复杂）。
您可能有一个用户 table，例如 :-
@Entity(tableName = "user")
public class User {
@PrimaryKey
Long id;
String userName;
String userEmail;
String userPassword;
public User(){};
@Ignore
public User(String userName, String userEmail, String userPassword) {
this.userName = userName;
this.userEmail = userEmail;
this.userPassword = userPassword;
}
}
link 用户使用他们最喜欢的模板并允许用户使用其他用户使用的模板，则需要 many-many 关系。因此，收藏夹 table 可以是用户和他们喜欢的模板之间的映射。要映射，您需要的只是用户的唯一标识符以及模板的唯一标识符（例如，每个模板的 id 列）。因此，收藏夹 table 可能是：-
/*
Mapping Table for many-many relationship between users and templates
*/
@Entity(
tableName = "favourite",
foreignKeys = {
@ForeignKey(
entity = User.class,
parentColumns = {"id"},
childColumns = {"userId"},
onDelete = CASCADE,
onUpdate = CASCADE
),
@ForeignKey(
entity = SingleTemplate.class,
parentColumns = {"id"},
childColumns = {"templateId"},
onDelete = CASCADE,
onUpdate = CASCADE
)
},
/* composite Primary Key */
primaryKeys = {"userId","templateId"},
indices = {@Index("templateId")}
)
public class Favourites {
long userId;
long templateId;
public Favourites(){}
@Ignore
public Favourites(long userId,long templateId) {
this.userId = userId;
this.templateId = templateId;
}
}
- 这种 table 有很多术语，例如关联 table、引用 table、映射 table ....
- ForeignKey 定义定义了 managing/asserting 参照完整性的规则，它们不是必需的，但它们很有用
- 它们可以防止添加孤儿 children。也就是说，如果尝试在相应 parent 中不存在列值的行中添加行，则会发生外键冲突（参见 Dao）。
- onDelete = CASCADE 将级联删除 parent，以便删除 child 中引用 parent 的所有行。
- onUpdate 类似，但它只会导致在 children 中更改引用的列，并且仅当引用的列发生更改时（这种情况很少发生）。
- 有两个外键定义，一个用于 reference/relationship 到用户 table，另一个用于 refrence/relationship 到 SingleTemplates table。
- templateId 列上的索引不是必需的，但如果省略 Room 会发出警告。
在此阶段可以添加用于插入和检索用户和收藏夹的 Dao。然而，检索收藏夹并不是用户友好的，它们只是没有什么意义的数字。例如
- 1,13 确实意味着 ID 为 1 的用户对 ID 为 13 的模板具有 link ....
因此，您可能希望获取用户详细信息以及模板详细信息。 Room 使这很容易做到你创建一个 POJO class （不是实体），你 Embed 一个实体然后定义一个与另一个class的关系 （嵌入用户与模板)。但是，由于映射 table 在您 之间（仅嵌入和关系满足 one-many 关系） 那么您需要一个 Association 定义了三个 tables.
之间的 Junction这样一个 suitable POJO 可以是 UserWithFavourites:-
public class UserWithFavourites {
@Embedded
User user; /* One User */
@Relation(entity = SingleTemplate.class, parentColumn = "id",entityColumn = "id",
associateBy = @Junction(value = Favourites.class,parentColumn = "userId",entityColumn = "templateId"))
List<SingleTemplate> singleTemplateList; /* A list of Templates for the User */
}
因此需要 Dao 来检索（查询）数据库。所以 SingleTemplateDao 现在可以是 :-
@Dao
interface SingleTemplateDao {
@Insert(onConflict = REPLACE)
long insert(SingleTemplate singleTemplate);
@Insert(onConflict = REPLACE)
long[] insert(SingleTemplate...singleTemplates);
@Insert(onConflict = REPLACE)
long[] insert(User...users);
@Insert(onConflict = IGNORE)
long[] insert(Favourites...favourites);
@Update
int update(SingleTemplate...singleTemplate);
@Query("SELECT * FROM templates WHERE template_type IN (:arrayOfTypes)")
List<SingleTemplate> getTemplatesByTypes(int[] arrayOfTypes);
@Query("SELECT * FROM user")
List<User> getAllUsers();
@Query("SELECT * FROM user WHERE id=:userId")
User getUserById(long userId);
@Query("SELECT * FROM User")
List<UserWithFavourites> getAllUsersWithFavourites();
}
示例 3
请注意，上面的 insert/updating 和提取代码已移至方法 na编辑示例 2。已创建新方法 example3 来演示添加用户和收藏夹 table，因此 activity 代码现在为：-
public class MainActivity 扩展 AppCompatActivity {
RoomDBSingleTemplate db; SingleTemplateDao dao; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); db = RoomDBSingleTemplate.getInstance(this); dao = db.getSingleTemplateDao(); example2(); example3(); } private void example3() { /* Add some Users */ dao.insert(new User("Fred","Fred@email.com","password"), /*ID will be 1 */ new User("Mary","Mary@email.com","password"), /* ID will be 2 */ new User("Sarah","Sarah@email.com","password") /* ID will be 3 */); /* Using the existing templates map/associate/relate users to templates */ dao.insert(new Favourites(1,1), new Favourites(1,3), new Favourites(1,4) /* UNKNOWN TYPE */, new Favourites(1,10), new Favourites(2,5), new Favourites(2,6), new Favourites(2,7), new Favourites(2,8), new Favourites(3,9), new Favourites(3,11), new Favourites(3,12), new Favourites(3,13), new Favourites(3,14)); /* extract all users with thier templates and then output the results to the log */ List<UserWithFavourites> userWithFavourites = dao.getAllUsersWithFavourites(); for (UserWithFavourites uwf: userWithFavourites) { Log.d("FAVOURITESINFO", "User is " + uwf.user.userName + " email is " + uwf.user.userEmail + " password is " + uwf.user.userPassword + " USERID = " + uwf.user.id + " # of Templates = " + uwf.singleTemplateList.size() ); for (SingleTemplate st: uwf.singleTemplateList) { Log.d("FAVOURITESINFO","Template is " + st.title + " Link is " + st.imageLink + " Type is " + getType(st.templateType) + " ID is " + st.id); } } } private void example2() { // Add one of each type individually long id = dao.insert(new SingleTemplate("Template1","Link1",SingleTemplate.MY_TEMPLATE)); dao.insert(new SingleTemplate("Template2","Link2", ANIMAL_TEMPLATE)); dao.insert(new SingleTemplate("Template3","Link3",SingleTemplate.PEOPLE_TEMPLATE)); // Add an unknown type dao.insert(new SingleTemplate("Template4","LINK4",99999)); // Add many templates type determined according to iteration int limit = 10; SingleTemplate[] stList = new SingleTemplate[limit]; for(int i=0; i < limit; i++) { stList[i] = new SingleTemplate( "Template" + (i+100), "Link" + (i+100), i % 3 ); } dao.insert(stList); // Get just Animal templates and update the Link by prefixing with ANIMAL List<SingleTemplate> animalTemplates = dao.getTemplatesByTypes(new int[]{ANIMAL_TEMPLATE}); stList = new SingleTemplate[animalTemplates.size()]; int i=0; for (SingleTemplate s: animalTemplates) { s.imageLink = "ANIMAL" + s.imageLink; stList[i++] = s; } dao.update(stList); // Get all known types and output to the log List<SingleTemplate> allTemplates = dao.getTemplatesByTypes(new int[]{MY_TEMPLATE,ANIMAL_TEMPLATE,PEOPLE_TEMPLATE}); for(SingleTemplate s: allTemplates) { Log.d("TEMPLATEINFO", "Title is " + s.title + " Link is " + s.imageLink + " Type is " + SingleTemplate.getType(s.templateType) + " ID is " + s.id ); } }}
示例3结果当运行（第一次）日志包括：-
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template1 Link is Link1 Type is MY ID is 1
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template3 Link is Link3 Type is PEOPLE ID is 3
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template4 Link is LINK4 Type is UNKNOWN ID is 4
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template105 Link is ANIMALANIMALLink105 Type is ANIMAL ID is 10
2021-06-09 11:50:11.477 D/FAVOURITESINFO: User is Mary email is Mary@email.com password is password USERID = 2 # of Templates = 4
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template100 Link is Link100 Type is MY ID is 5
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template101 Link is Link101 Type is PEOPLE ID is 6
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template102 Link is ANIMALANIMALLink102 Type is ANIMAL ID is 7
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template103 Link is Link103 Type is MY ID is 8
2021-06-09 11:50:11.477 D/FAVOURITESINFO: User is Sarah email is Sarah@email.com password is password USERID = 3 # of Templates = 5
2021-06-09 11:50:11.477 D/FAVOURITESINFO: Template is Template104 Link is Link104 Type is PEOPLE ID is 9
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template106 Link is Link106 Type is MY ID is 11
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template107 Link is Link107 Type is PEOPLE ID is 12
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template108 Link is ANIMALANIMALLink108 Type is ANIMAL ID is 13
2021-06-09 11:50:11.478 D/FAVOURITESINFO: Template is Template109 Link is Link109 Type is MY ID is 14