我们需要什么：
我们需要能够使用将外部数据库附加到
内部房间数据库，而不更改它们存储的路径。
添加它们之后，我们希望能够将数据库与
Room Entity、Dao 和 Database 对象。有没有可能的方法
实现这个？
不附加可能更容易，原因是您可以使用单独的房间数据库实例。如果没有你需要有单独的 DAO 来满足附加的模式名称（我相信）。说下面的例子（基于我为某人玩的东西，因此列名相当混乱）。
例如假设ATTACH DATABASE .... AS other（附加的架构是other）然后代替（对于主数据库）
@Query("SELECT * FROM AllUsers")
List<AllUsers> getAllAllUsers();
你需要一个免费的：-
@SkipQueryVerification
@Query("SELECT * FROM other.AllUsers")
List<AllUsers> getOtherAllAllUsers();
等等
但是，如果你有类似（主要）的东西：-
mLPDB = Room.databaseBuilder(this,LoanPaymentDatabase.class,"mydb").allowMainThreadQueries().build();
mLPDB_DAO = mLPDB.mDao();
与（为其他）一起：-
mOtherDB = Room.databaseBuilder(this,LoanPaymentDatabase.class,OtherDatabaseHelper.DBNAME).allowMainThreadQueries().build();
mOtherDAO = mOtherDB.mDao();
然后您可以使用相同的 DAO 访问两者。
不一定准确？
还包括评论：-
您必须先将数据迁移到房间本身。
玩一会，您可以通过将 user_version 设置为 0 来欺骗 Room，从而绕过 必须迁移。在这种情况下，Room 会设置版本号（有限测试）。但是，我不确定 GreenDao 或您的服务器会怎么做（您的作业）。
我的有限测试是针对一个常见问题，即迁移具有整数主键的列（即没有自动增量）的问题。如果迁移房间会抱怨架构不匹配。所以我故意不编码AUTOINCREMENT，将user_version设置为0，并且没有抱怨通过Room访问数据库。还使用了 rumplestilskin 的列类型，没有任何抱怨。
因此，我相信您可以通过将 user_version 设置为 0 来解决令人恐惧的预期/发现的迁移问题（因此我相信可以规避迁移）。显然，尽管列名必须匹配，但如果在实体中定义且未被忽略。
- 我还尝试添加一个未定义实体的列，并使用上述结果没有任何投诉（这些测试在下面的代码中应该很明显）。
示例
以下是一个 2 Entity Room 数据库的示例，为了测试 other 数据库，一个在房间外构建的数据库与房间数据库充分匹配以便能够使用，即实体列名称匹配。
另一个数据库
另一个非房间数据库是通过 SQLiteOpenHelper 子类根据 OtherDatabaseHelper.java 创建的：-
public class OtherDatabaseHelper extends SQLiteOpenHelper {
public static final String DBNAME = "lpolddb";
public static final int DBVERSION = 1;
public static final String ALLUSERS_TBL = "AllUsers";
public static final String PAIDUNPAID_TBL = "PaidUnpaid";
/*
@PrimaryKey(autoGenerate = true)
private long auid;
private String Name;
private int Loan;
private int TimeInMonths;
*/
public static final String ALLUSERS_COL_AUID = "auid";
public static final String ALLUSERS_COL_NAME = "Name";
public static final String ALLUSERS_COL_LOAN = "Loan";
public static final String ALLUSERS_COL_TIMEINMONTHS = "TimeInMonths";
private static final String crt_allusers_table_sql =
"CREATE TABLE IF NOT EXISTS " + ALLUSERS_TBL + "(" +
//ALLUSERS_COL_AUID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
ALLUSERS_COL_AUID + " INTEGER PRIMARY KEY," +
ALLUSERS_COL_NAME + " TEXT, " +
ALLUSERS_COL_LOAN + " INTEGER, " +
"someothercolumnnotdefineinroom TEXT, " + //!!!!!!!!!! not a column in an entity
ALLUSERS_COL_TIMEINMONTHS + " INTEGER" +
")";
/*
@PrimaryKey(autoGenerate = true)
private long puid;
private int TimeInMonths;
private String PaidUnpaid;
@ForeignKey(
entity = AllUsers.class,
parentColumns = {"auid"},
childColumns = {"AllUsersReference"},
onUpdate = ForeignKey.CASCADE, onDelete = ForeignKey.CASCADE)
private long AllUsersReference;
*/
public static final String PAIDUNPAID_COL_PUID = "puid";
public static final String PAIDUNPAID_TIMEINMONTHS = ALLUSERS_COL_TIMEINMONTHS;
public static final String PAIDUNPAID_COL_PAIDUNPAID = "PaidUnpaid";
public static final String PAIDUNPAID_COL_ALLUSERSREFERENCE = "AllUsersReference";
public static final String crt_paidunpaid_table_sql =
"CREATE TABLE IF NOT EXISTS " + PAIDUNPAID_TBL + "(" +
PAIDUNPAID_COL_PUID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
PAIDUNPAID_TIMEINMONTHS + " rumplestilskin, " + // !!!!!!!!!!!
PAIDUNPAID_COL_PAIDUNPAID + " TEXT," +
PAIDUNPAID_COL_ALLUSERSREFERENCE + " INTEGER " +
" REFERENCES " + ALLUSERS_TBL + "(" + ALLUSERS_COL_AUID + ") " +
"ON UPDATE CASCADE ON DELETE CASCADE" +
")";
SQLiteDatabase mDB;
public OtherDatabaseHelper(Context context) {
super(context, DBNAME, null, DBVERSION);
mDB = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(crt_allusers_table_sql);
db.execSQL(crt_paidunpaid_table_sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public long insertAllUsers(String name, int loanamount, int periodofloan) {
ContentValues cv = new ContentValues();
cv.put(ALLUSERS_COL_NAME,name);
cv.put(ALLUSERS_COL_LOAN,loanamount);
cv.put(ALLUSERS_COL_TIMEINMONTHS,periodofloan);
return mDB.insert(ALLUSERS_TBL,null,cv);
}
public long insertPaidUnpaid(int formonth, String status, long allUserreferenced) {
ContentValues cv = new ContentValues();
cv.put(PAIDUNPAID_TIMEINMONTHS,formonth);
cv.put(PAIDUNPAID_COL_PAIDUNPAID,status);
cv.put(PAIDUNPAID_COL_ALLUSERSREFERENCE,allUserreferenced);
return mDB.insert(PAIDUNPAID_TBL,null,cv);
}
}
- 查看 cmets 了解异常/故意添加的差异
- 这是填充的，由备用 Room 数据库访问，并通过下面 MainActivity.java 中的附加数据库
房间数据库
两个实体：-
AllUsers.java
@Entity
public class AllUsers {
@PrimaryKey(autoGenerate = true)
private long auid;
private String Name;
private int Loan;
private int TimeInMonths;
public AllUsers() {
}
@Ignore
public AllUsers(String Name, int Loan, int TimeInMonths) {
this.Name = Name;
this.Loan = Loan;
this.TimeInMonths = TimeInMonths;
}
public long getAuid() {
return auid;
}
public void setAuid(long auid) {
this.auid = auid;
}
public String getName() {
return Name;
}
public void setName(String name) {
Name = name;
}
public int getLoan() {
return Loan;
}
public void setLoan(int loan) {
Loan = loan;
}
public int getTimeInMonths() {
return TimeInMonths;
}
public void setTimeInMonths(int timeInMonths) {
TimeInMonths = timeInMonths;
}
}
和 PaidUnpaid.java :-
@Entity
public class PaidUnpaid {
@PrimaryKey(autoGenerate = true)
private long puid;
private int TimeInMonths;
private String PaidUnpaid;
@ForeignKey(
entity = AllUsers.class,
parentColumns = {"auid"},
childColumns = {"AllUsersReference"},
onUpdate = ForeignKey.CASCADE, onDelete = ForeignKey.CASCADE)
private long AllUsersReference;
public PaidUnpaid() {
}
@Ignore
public PaidUnpaid(int TimeInMonths, String PaidUnpaid, long AllUsersreference) {
this.TimeInMonths = TimeInMonths;
this.PaidUnpaid = PaidUnpaid;
this.AllUsersReference = AllUsersreference;
}
public long getPuid() {
return puid;
}
public void setPuid(long puid) {
this.puid = puid;
}
public int getTimeInMonths() {
return TimeInMonths;
}
public void setTimeInMonths(int timeInMonths) {
TimeInMonths = timeInMonths;
}
public String getPaidUnpaid() {
return PaidUnpaid;
}
public void setPaidUnpaid(String paidUnpaid) {
PaidUnpaid = paidUnpaid;
}
public long getAllUsersReference() {
return AllUsersReference;
}
public void setAllUsersReference(long allUsersReference) {
AllUsersReference = allUsersReference;
}
}
一个附加的 POJO 类，AllUsersAndPaidUnpaidsList.java，它被如此合并和使用：-
public class AllUsersAndPaidUnpaidsList {
@Embedded
AllUsers allUsers;
@Ignore
@PrimaryKey
long auid;
@Ignore
@Relation(entity = PaidUnpaid.class,parentColumn = "auid",entityColumn = "puid")
List<PaidUnpaid> paidUnpaidList;
@Ignore
public AllUsersAndPaidUnpaidsList(AllUsers au, List<PaidUnpaid> pulist) {
this.allUsers = au;
this.paidUnpaidList = pulist;
}
public List<PaidUnpaid> getPaidUnpaidList() {
return this.paidUnpaidList;
}
public void setPaidUnpaidList(List<PaidUnpaid> paidUnpaidList) {
this.paidUnpaidList = paidUnpaidList;
}
public AllUsers getAllUsers() {
return allUsers;
}
public void setAllUsers(AllUsers allUsers) {
this.allUsers = allUsers;
}
public void outputToLog(String tag) {
StringBuilder sb = new StringBuilder("AllUsersName = ")
.append(this.allUsers.getName())
.append(" TimeInMonths = ")
.append(String.valueOf(this.allUsers.getTimeInMonths()))
;
for (PaidUnpaid pu: this.getPaidUnpaidList()) {
sb.append("\n\t TimeInMonths = ")
.append(String.valueOf(pu.getTimeInMonths()))
.append(" Paid/Unpaid = ")
.append(pu.getPaidUnpaid());
}
Log.d(tag,sb.toString());
}
}
单一界面Dao.java :-
@androidx.room.Dao
public interface Dao {
@Insert(onConflict = OnConflictStrategy.IGNORE)
long[] insertAllUsers(AllUsers... allUsers);
@Insert(onConflict = OnConflictStrategy.IGNORE)
long insertAllUsers(AllUsers allUsers);
@Insert(onConflict = OnConflictStrategy.IGNORE)
long[] insertPaidUnpaid(PaidUnpaid... paidUnpaids);
@Insert(onConflict = OnConflictStrategy.IGNORE)
long insertPaidUnpaid(PaidUnpaid paidUnpaid);
@Update(onConflict = OnConflictStrategy.IGNORE)
int updateAllUsers(AllUsers... allUsers);
@Update(onConflict = OnConflictStrategy.IGNORE)
int updateAllUsers(AllUsers allUsers);
@Update(onConflict = OnConflictStrategy.IGNORE)
int updatePaidUnpaid(PaidUnpaid... paidUnpaids);
@Update(onConflict = OnConflictStrategy.IGNORE)
int updatePaidUnpaid(PaidUnpaid paidUnpaid);
@Delete
int deleteAllUsers(AllUsers... allUsers);
@Delete
int deleteAllUsers(AllUsers allUsers);
@Delete
int deletePaidUnpaid(PaidUnpaid... paidUnpaids);
@Delete
int deletePaidUnpaid(PaidUnpaid paidUnpaid);
@Query("SELECT * FROM AllUsers")
List<AllUsers> getAllAllUsers();
@Query("SELECT * FROM AllUsers WHERE auid = :id")
List<AllUsers> getOneAllUsersById(long id);
@Query("SELECT * FROM PaidUnpaid")
List<PaidUnpaid> getAllPaidUnpaids();
@Query("SELECT * FROM PaidUnpaid WHERE puid = :id")
List<PaidUnpaid> getOnePaidUnpaidById(long id);
@Query("SELECT * FROM PaidUnpaid WHERE AllUsersReference = :allUsersid")
List<PaidUnpaid> getPaidUnpaidsForAllUsersId(long allUsersid);
/*************
* Some Additional DAO's for attached not required for alternative helper
* in practice you would likely need attached versions of all
************/
@Query("SELECT * FROM other.PaidUnpaid WHERE AllUsersReference = :allUsersid")
@SkipQueryVerification
List<PaidUnpaid> getOtherPaidUnpaidForAllUsersId(long allUsersid);
@SkipQueryVerification
@Query("SELECT * FROM other.AllUsers")
List<AllUsers> getOtherAllAllUsers();
}
房间数据库类 LoanPaymentDatabase.java
@Database(entities = {AllUsers.class,PaidUnpaid.class},exportSchema = false,version = 1)
public abstract class LoanPaymentDatabase extends RoomDatabase {
public abstract Dao mDao();
}
把它们放在一起
最后一个活动：-
创建并填充 other（非房间）数据库（如果不存在）以进行测试。 将 user_version（Android talk 中的数据库版本）设置为 0。
如果需要，创建数据库的 Room 版本。
- 向 Room 版本添加几行。
- 将 Room 版本中的数据输出到日志中。
- 使用 other 数据库创建备用 RoomDatabase。
- 通过 Room 输出 other 数据库中的数据。
- 将 other 数据库附加到 Room 版本。
- 通过包含 other.???? 的附加 DAO 接口通过原始 Roomdatabase 访问附加的 other 数据库从两者中输出数据。
MainActivity.java
public class MainActivity extends AppCompatActivity {
LoanPaymentDatabase mLPDB;
Dao mLPDB_DAO;
LoanPaymentDatabase mOtherDB;
Dao mOtherDAO;
Random rnd = new Random();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
manageOtherDatabase();
mLPDB = Room.databaseBuilder(this,LoanPaymentDatabase.class,"mydb").allowMainThreadQueries().build();
mLPDB_DAO = mLPDB.mDao();
// Add some(2) AllUsers
mLPDB_DAO.insertAllUsers(new AllUsers("Fred",5000,5));
mLPDB_DAO.insertAllUsers(new AllUsers("Mary", 4000,6));
// Add Some PaidUnpaid's for each AllUsers
// Random amount with random paid or unpaid
// This is just for demonstration and doesn't reflect what would typically be done
List<AllUsers> allusers = mLPDB_DAO.getAllAllUsers();
for (AllUsers au: allusers) {
int lc = rnd.nextInt(4) + 1;
int month = 1;
for (int i=0; i < lc; i++) {
String paid = "Paid";
if((rnd.nextInt(2) % 2) > 0 ) {
paid = "Unpaid";
}
mLPDB_DAO.insertPaidUnpaid(new PaidUnpaid(month++, paid, au.getAuid()));
}
}
//Extract all AllUsersAndPaidUnpaid (i.e each AllUsers with the related PaidUnpaid for the AllUsers)
ArrayList<AllUsersAndPaidUnpaidsList> aupulist = new ArrayList<>();
for (AllUsers au: allusers) {
List<PaidUnpaid> pulist = mLPDB_DAO.getPaidUnpaidsForAllUsersId(au.getAuid());
aupulist.add(new AllUsersAndPaidUnpaidsList(au,pulist));
}
// Output the results
for (AllUsersAndPaidUnpaidsList aupu: aupulist) {
aupu.outputToLog("INITALAUPU");
}
//Use separate openHelper rather than ATTACH
mOtherDB = Room.databaseBuilder(this,LoanPaymentDatabase.class,OtherDatabaseHelper.DBNAME).allowMainThreadQueries().build();
mOtherDAO = mOtherDB.mDao();
ArrayList<AllUsersAndPaidUnpaidsList> otheraupulist = new ArrayList<>();
for (AllUsers oau: mOtherDAO.getAllAllUsers() ) {
otheraupulist.add(new AllUsersAndPaidUnpaidsList(oau,mOtherDAO.getPaidUnpaidsForAllUsersId(oau.getAuid())));
}
for (AllUsersAndPaidUnpaidsList aupu: otheraupulist) {
aupu.outputToLog("ALTDBAUPU");
}
// User Attach
SupportSQLiteDatabase main_sdb = mLPDB.getOpenHelper().getWritableDatabase();
SupportSQLiteDatabase other_sdb = mOtherDB.getOpenHelper().getWritableDatabase();
main_sdb.execSQL("ATTACH DATABASE '" + other_sdb.getPath() + "' AS other");
ArrayList<AllUsersAndPaidUnpaidsList> attachaupulist = new ArrayList<>();
for (AllUsers aau: mLPDB_DAO.getAllAllUsers()) {
attachaupulist.add(new AllUsersAndPaidUnpaidsList(aau,mLPDB_DAO.getPaidUnpaidsForAllUsersId(aau.getAuid())));
}
for (AllUsers aauother: mLPDB_DAO.getOtherAllAllUsers()) {
attachaupulist.add(new AllUsersAndPaidUnpaidsList(aauother,mLPDB_DAO.getOtherPaidUnpaidForAllUsersId(aauother.getAuid())));
}
for (AllUsersAndPaidUnpaidsList aupu: attachaupulist) {
aupu.outputToLog("ATTACHEDAUPU");
}
mLPDB.close();
}
/*********
* For testing purposes - Populate the OTHER database to be used
*********/
private void manageOtherDatabase() {
OtherDatabaseHelper mODBHlpr = new OtherDatabaseHelper(this);
SQLiteDatabase db = mODBHlpr.getWritableDatabase();
db.execSQL("PRAGMA user_version = 0");
if (DatabaseUtils.queryNumEntries(db,OtherDatabaseHelper.ALLUSERS_TBL) > 0) {
db.close();
mODBHlpr.close();
return;
}
db.beginTransaction();
for (int i= 0; i < 5; i++) {
long auid = mODBHlpr.insertAllUsers("AU" + String.valueOf(i),10000 + 1,5 + i);
for(int ii = 0; ii < 5; ii++) {
mODBHlpr.insertPaidUnpaid(ii,"Paid",auid);
}
}
db.setTransactionSuccessful();
db.endTransaction();
db.close();
mODBHlpr.close();
}
}