如何使用 Room 的 prepackagedDatabaseCallback？
How do I use Room's prepackagedDatabaseCallback?
版本 2.3.0-alpha03 Room 有一个 prepackagedDatabaseCallback 上面写着：-
-
This callback will be invoked after the pre-package DB is copied but before Room had a chance to open it and therefore before the RoomDatabase.Callback methods are invoked. This callback can be useful for updating the pre-package DB schema to satisfy Room's schema validation.
那么我如何使用它来规避无效架构 expected .... found ....?
我可以用这个来介绍触发器吗，因为房间没有创建触发器的注释？
So how could I uses this to circumvent the Invalid Schema expected .... found ....?
以下虽然冗长，但显示了相应更正架构的示例。
Could I use this to introduce Triggers, as room doesn't have annotations for the creation of triggers?
是的，虽然这还没有实际测试过，但这个例子是为了创建触发器。
对示例重新评分的注释
首先，应该注意的是，当最初查看回调时存在问题。这些问题现已得到解决 但是 需要 2.4.0-beta02 或更高版本。问题是：-
- 不允许预打包数据库中的版本 0（通常是这种情况）
- 空数据库传递给 PrePackagedDatabaseCallback
- PrePackagedDatabaseCallback 中应用的数据库更新Lost/Undone
应用的修复
-
Correctly open pre-package database during PrepackagedDatabaseCallback invocation.
-
The actual pre-package database was not being opened because only the file name was being used when creating the temporary open helper instead of the full path. The framework open helper will only open an existing file if the name of the database is a path (starts with '/') otherwise it create a new file. This changes fixes it by using the absolute file path as name.
流
当控制传递给回调时，资产数据库已被复制。因此，从理论上讲，这只是更改 TABLES 和 VIEWS（如果有的话）以匹配房间期望的架构的问题。
经常尝试将房间的期望与房间的发现相匹配会让一些人感到沮丧。下面的示例将克服 minor/small/often 遗漏的问题。它的工作原理是：-
- 删除除 table 之外的所有非 sqlite 或非 android 组件（即来自复制资产数据库的视图、索引和触发器），
- 重命名 tables 以允许创建房间期望的那些，
- 正在使用 Room 的预期架构创建新的 tables，
- 从 Room 生成的 java 复制而来[=146=]
- 正在将重命名的（资产）table 中的数据复制到新创建的 table 中
- INSERT OR IGNORE已经被使用所以约束冲突，比如NOT NULL, UNIQUE, CHECK不会导致异常（把
INSERT OR IGNORE改成INSERT 会失败）
- 创建 Room 期望的其他组件（视图、索引和触发器（注意 Room 只有 FTS tables 的触发器））。
- 删除现在多余的重命名 tables
- 正在执行 VACUUM 清理数据库，
- 最后添加任何触发器。
确实希望源（资产）的列顺序正确，空值不包含在具有 NOT NULL 约束的列中。但是，由于使用了 INSERT OR IGNORE，因此不会插入此类行而不是导致异常。
除了从生成的 java 中复制代码外，该过程是自动化的，无需修改即可处理 most/many 资产。
代码
绝大部分代码在@Database class OtherDatabase 中。请注意，这应该可以通过一些调整来应对许多数据库 （请参阅要进行的更改的注释）:-
@SuppressLint({"Range"}) /*<<<<< used due to bug/issue with getColumnIndex introduced with SDK 31 */
@Database(
entities = {Person.class, Company.class, CompanyPersonMap.class}, //<<<<< CHANGED ACCORDINGLY
version = OtherDatabase.DATABASE_VERSION, /* note due to shared usage of DBVERSION OtherDatabase used <<<<< CHANGE ACCORDINGLY */
exportSchema = false /* change to suit */
)
@TypeConverters({AllTypeConverters.class})
abstract class OtherDatabase extends RoomDatabase {
public static final String DATABASE_NAME = "otherprepackageddatabasecallbacktest.db"; //<<<<< CHANGE AS REQUIRED
public static final int DATABASE_VERSION = 1; //<<<<< CHANGE AS REQUIRED
public static final String ASSET_FILE_NAME = "prepackageddatabasecallbacktest.db"; //<<<<< CHANGED AS REQUIRED
/**
* sqlite_master table and column names !!!!!DO NOT CHANGE!!!!!
*/
private static final String SQLITE_MASTER_TABLE_NAME = "sqlite_master";
private static final String SQLITE_MASTER_COL_NAME = "name";
private static final String SQLITE_MASTER_COL_TYPE = "type";
private static final String SQLITE_MASTER_COL_TABLE_NAME = "tbl_name";
private static final String SQLITE_MASTER_COL_SQL = "sql";
abstract AllDao getAllDao(); //<<<<< CHANGE ACCORDINGLY
private static volatile OtherDatabase instance = null; //<<<<< CHANGE ACCORDINGLY
public static OtherDatabase /*<<<< CHANGE ACCORDINGLY */ getInstance(Context context) {
if (instance == null) {
instance = Room.databaseBuilder(context, OtherDatabase.class, OtherDatabase.DATABASE_NAME)
.allowMainThreadQueries() /*<<<<< USED FOR BREVITY CONVENIENCE */
.createFromAsset(ASSET_FILE_NAME, prePkgDbCallback) /* 2nd parameter is the THE CALL BACK to invoke */
.build();
}
return instance;
}
/* THE CALLBACK */
static final PrepackagedDatabaseCallback prePkgDbCallback = new PrepackagedDatabaseCallback() {
final static String assetTablePrefix = "asset_"; /* prefix used for renamed tables - should not need to be changed */
private List<SQLiteMasterComponent> sqLiteMasterComponentArray; /* store for sqlite_master extract */
@Override
public void onOpenPrepackagedDatabase(@NonNull SupportSQLiteDatabase db) {
super.onOpenPrepackagedDatabase(db);
sqLiteMasterComponentArray = buildComponentsList(db); /* gets relevant rows from sqlite_master */
dropNonTableComponents(sqLiteMasterComponentArray,db); /* everything except the tables */
renameTableComponents(sqLiteMasterComponentArray, assetTablePrefix,db); /* rename the tables using prefix */
/*<<<<< TAILOR (the db.execSQL's below) AS APPROPRIATE - SEE COMMENTS THAT FOLLOW >>>>>*/
/* copied from the @Database classes generated java e.g. leave indexes till later
_db.execSQL("CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`))");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_firstName` ON `Person` (`firstName`)");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_lastName` ON `Person` (`lastName`)");
_db.execSQL("CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))");
_db.execSQL("CREATE TABLE IF NOT EXISTS `company_person_map` (`companyid_map` INTEGER NOT NULL, `personid_map` INTEGER NOT NULL, PRIMARY KEY(`companyid_map`, `personid_map`), FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE , FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_company_person_map_personid_map` ON `company_person_map` (`personid_map`)");
*/
/* Create the tables as per Room definitions - ***** CREATE TABLES COPIED FROM GENERATED JAVA *****
only indexes, views, triggers (for FTS) should be done after the data has been copied so :-
data is loaded faster as no index updates are required.
triggers don't get triggered when loading the data which could result in unexpected results
*/
db.execSQL("CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`));");
db.execSQL("CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))");
db.execSQL("CREATE TABLE IF NOT EXISTS `company_person_map` (`companyid_map` INTEGER NOT NULL, `personid_map` INTEGER NOT NULL, PRIMARY KEY(`companyid_map`, `personid_map`), FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE , FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )");
copyData(sqLiteMasterComponentArray, assetTablePrefix,db); /* copy the data from the renamed asset tables to the newly created Room tables */
/* Create the other Room components - ***** CREATE ? COPIED FROM GENERATED JAVA *****
Now that data has been copied create other Room components indexes, views and triggers
(triggers would only be for FTS (full text search))
again sourced from generated Java
*/
db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_firstName` ON `Person` (`firstName`)");
db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_lastName` ON `Person` (`lastName`)");
db.execSQL("CREATE INDEX IF NOT EXISTS `index_company_person_map_personid_map` ON `company_person_map` (`personid_map`)");
dropRenamedTableComponents(sqLiteMasterComponentArray, assetTablePrefix,db); /* done with the renamed tables so drop them */
db.execSQL("VACUUM"); /* cleanup the database */
createTriggers(sqLiteMasterComponentArray,db); /* create any triggers */
}
};
static int dropNonTableComponents(List<SQLiteMasterComponent> components, SupportSQLiteDatabase db) {
int rv = 0;
for(SQLiteMasterComponent c: components) {
if (!c.type.equals("table") ) {
db.execSQL("DROP " + c.type + " IF EXISTS " + c.name);
rv++;
}
}
return rv;
}
static int dropRenamedTableComponents(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
int maxForeignKeyCount = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount > maxForeignKeyCount) {
maxForeignKeyCount = c.foreignKeyCount;
}
}
for (int i= maxForeignKeyCount; i >= 0; i--) {
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount == i) {
db.execSQL("DROP " + c.type + " IF EXISTS " + prefix + c.name);
rv++;
}
}
}
return rv;
}
static int renameTableComponents(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
db.execSQL("PRAGMA foreign_keys = ON"); // Just in case turn foreign keys on
for(SQLiteMasterComponent c: components) {
if (c.type.equals("table")) {
db.execSQL("ALTER TABLE " + c.name + " RENAME TO " + prefix + c.name);
rv++;
}
}
return rv;
}
/*
NOTE tables with fewest Foreign Key definitions done first
NOTE makes an assumption that this will not result in FK conflicts
TODO should really be amended to ensure that a table with FK's is only attempted when all of it's parent tables have been loaded
*/
static int copyData(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
int maxForeignKeyCount = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount > 0) {
maxForeignKeyCount = c.foreignKeyCount;
}
}
for (int i=0; i <= maxForeignKeyCount; i++) {
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount == i) {
db.execSQL("INSERT OR IGNORE INTO " + c.name + " SELECT * FROM " + prefix + c.name + ";");
rv++;
}
}
}
return rv;
}
static int createTriggers(List<SQLiteMasterComponent> components, SupportSQLiteDatabase db) {
int rv = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("trigger")) {
//TODO should really check if the sql includes IF NOT EXISTSand if not add IF NOT EXISTS
db.execSQL(c.sql);
rv++;
}
}
return rv;
}
/**
* Build the list of required SQLiteMasterComponents to save having to access
* sqlite_master many times.
* @param db the SupportSQliteDatabase to access
* @return the list of SQliteMasterComponents extracted
*/
@SuppressLint("Range")
static List<SQLiteMasterComponent> buildComponentsList(SupportSQLiteDatabase db) {
final String FOREIGN_KEY_FLAG_COLUMN = "foreign_key_flag";
ArrayList<SQLiteMasterComponent> rv = new ArrayList<>();
Cursor csr = db.query("SELECT *," +
/* Column to indicate wherther or not FK constraints appear to have been defined
* NOTE!! can be fooled
* e.g. if a column is defined as `my badly named FOREIGN KEY column ` ....
* */
"(" +
"instr(" + SQLITE_MASTER_COL_SQL + ",'FOREIGN KEY') > 0) + " +
"(instr(" + SQLITE_MASTER_COL_SQL + ",' REFERENCES ')> 0) " +
"AS " + FOREIGN_KEY_FLAG_COLUMN + " " +
"FROM " + SQLITE_MASTER_TABLE_NAME + " " +
/* do not want any sqlite tables or android tables included */
"WHERE lower(" + SQLITE_MASTER_COL_NAME + ") NOT LIKE 'sqlite_%' AND lower(" + SQLITE_MASTER_COL_NAME + ") NOT LIKE 'android_%'");
while (csr.moveToNext()) {
SQLiteMasterComponent component = new SQLiteMasterComponent(
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_NAME)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_TYPE)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_TABLE_NAME)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_SQL)),
csr.getInt(csr.getColumnIndex(FOREIGN_KEY_FLAG_COLUMN)),
0);
if (csr.getInt(csr.getColumnIndex(FOREIGN_KEY_FLAG_COLUMN)) > 0) {
component.foreignKeyCount = component.getForeignKeyCount(db);
}
rv.add(component);
}
csr.close();
return (List<SQLiteMasterComponent>) rv;
}
/**
* Class to hold a row from sqlite_master
*/
private static class SQLiteMasterComponent {
private String name;
private String type;
private String owningTable;
private String sql;
private int foreignKeyFlag = 0;
private int foreignKeyCount = 0;
SQLiteMasterComponent(String name, String type, String owningTable, String sql, int foreignKeyFlag, int foreignKeyCount) {
this.name = name;
this.type = type;
this.owningTable = owningTable;
this.sql = sql;
this.foreignKeyFlag = foreignKeyFlag;
this.foreignKeyCount = foreignKeyCount;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public String getOwningTable() {
return owningTable;
}
public void setOwningTable(String owningTable) {
this.owningTable = owningTable;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
public int getForeignKeyFlag() {
return foreignKeyFlag;
}
public void setForeignKeyFlag(int foreignKeyFlag) {
this.foreignKeyFlag = foreignKeyFlag;
}
public boolean isForeignKey() {
return this.foreignKeyFlag > 0;
}
public int getForeignKeyCount() {
return foreignKeyCount;
}
public void setForeignKeyCount(int foreignKeyCount) {
this.foreignKeyCount = foreignKeyCount;
}
/**
* Retrieve the number of rows returned by PRAGMA foreign_key_list
* @param db The SupportSQLiteDatabase to access
* @return The number of rows i.e. number of Foreign Key constraints
*/
private int getForeignKeyCount(SupportSQLiteDatabase db) {
int rv =0;
Cursor csr = db.query("SELECT count(*) FROM pragma_foreign_key_list('" + this.name + "');");
if (csr.moveToFirst()) {
rv = csr.getInt(0);
}
csr.close();
return rv;
}
}
}
工作示例
资产数据库
资产数据库包含3个tables，person，company and company_person_map
人 DDL是
CREATE TABLE person (personid INTEGER PRIMARY KEY, firstName TEXT, lastName TEXT, middleNames TEXT, dateOfBirth DATE);
预计房间：-
CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`))
- 注意 dateOfBirth 列的 DATE v INTEGER 的类型，房间不接受所以 预期...找到....
公司 DDL 是
CREATE TABLE company (companyid INTEGER PRIMARY KEY, companyName TEXT, city TEXT, state TEXT, country TEXT, notes TEXT);
预计房间：-
CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))
- 两者都是可比的房间会接受
company_person_map DDL是
CREATE TABLE company_person_map (
companyid_map INTEGER NOT NULL REFERENCES company(companyid) ON DELETE CASCADE ON UPDATE CASCADE,
personid_map INTEGER NOT NULL REFERENCES person(personid) ON DELETE CASCADE ON UPDATE CASCADE,
PRIMARY KEY (companyid_map, personid_map));
预计房间：-
CREATE TABLE IF NOT EXISTS `company_person_map` (
`companyid_map` INTEGER NOT NULL,`personid_map` INTEGER NOT NULL,
PRIMARY KEY(`companyid_map`, `personid_map`),
FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE ,
FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )
- 虽然差别很大，但有可比性，房间可以接受
资产table包含以下数据：-
人
公司
company_person_map
- 人员 11 未映射到公司。
AllDao是
- none 的插入被使用，也不是所有的查询。
调用 Activity 是 :-
public class MainActivity extends AppCompatActivity {
OtherDatabase dbOther;
AllDao daoOther;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbOther = OtherDatabase.getInstance(this);
daoOther = dbOther.getAllDao();
for(Person p: daoOther.getAllPeople()) {
Log.d("DBINFO",
"Person is " + p.firstName
+ " " + p.middleNames
+ " " + p.lastName
+ " Date of Birth is " + p.dateOfBirth
+ " ID is " + p.id
);
}
for(CompanyWithPeople cwp: dao.getCompanyWithPeople()) {
logCompany(cwp.company,"DBINFO","");
for(Person p: cwp.person) {
logPerson(p,"DBINFO","\n\t");
}
}
}
void logCompany(Company c, String tag, String lineFeed) {
Log.d(tag,lineFeed + "Company is " + c.companyName
+ " Location is " + c.city + ", " + c.state + ", " + c.country
+ " ID is " + c.companyId
+ "\n\t Notes: " + c.notes
);
}
void logPerson(Person p, String tag, String lineFeed) {
Log.d(tag, lineFeed + p.firstName + " " + p.middleNames
+ " " + p.lastName + " Date of Birth is " + p.dateOfBirth
+ " ID is " + p.id
);
}
}
结果
2021-11-28 19:56:01.928 D/DBINFO: Person is Robert John Smith Date of Birth is Sat Dec 27 17:46:33 GMT+10:00 1969 ID is 1
2021-11-28 19:56:01.929 D/DBINFO: Person is Julie Mary Armstrong Date of Birth is Mon Jan 12 23:22:04 GMT+10:00 1970 ID is 2
2021-11-28 19:56:01.929 D/DBINFO: Person is Andrea Susan Stewart Date of Birth is Mon Jan 05 04:56:09 GMT+10:00 1970 ID is 3
2021-11-28 19:56:01.929 D/DBINFO: Person is Mary Belinda Allway Date of Birth is Mon Jan 12 00:15:21 GMT+10:00 1970 ID is 4
2021-11-28 19:56:01.929 D/DBINFO: Person is Lisa Elizabeth Brooks Date of Birth is Sat Jan 03 03:51:21 GMT+10:00 1970 ID is 5
2021-11-28 19:56:01.930 D/DBINFO: Person is Stephen Colin Cobbs Date of Birth is Tue Jan 06 14:01:55 GMT+10:00 1970 ID is 6
2021-11-28 19:56:01.930 D/DBINFO: Person is Breane Cath Davidson Date of Birth is Thu Jan 01 22:30:14 GMT+10:00 1970 ID is 7
2021-11-28 19:56:01.930 D/DBINFO: Person is Trevor Arthur Frankston Date of Birth is Sat Jan 10 03:47:02 GMT+10:00 1970 ID is 8
2021-11-28 19:56:01.930 D/DBINFO: Person is George Howard Erksine Date of Birth is Sun Jan 11 00:47:02 GMT+10:00 1970 ID is 9
2021-11-28 19:56:01.930 D/DBINFO: Person is Uriah Stanley Jefferson Date of Birth is Mon Dec 29 19:11:31 GMT+10:00 1969 ID is 10
2021-11-28 19:56:01.931 D/DBINFO: Person is Valerie Alana Singleton Date of Birth is Thu Jan 01 11:45:07 GMT+10:00 1970 ID is 11
2021-11-28 19:56:01.931 D/DBINFO: Person is Vladimir Oscar Whitworth Date of Birth is Sat Jan 10 00:29:45 GMT+10:00 1970 ID is 12
2021-11-28 19:56:01.936 D/DBINFO: Company is Allbright Construction Location is Sydney, NSW, Australia ID is 1
Notes:
2021-11-28 19:56:01.936 D/DBINFO: Julie Mary Armstrong Date of Birth is Mon Jan 12 23:22:04 GMT+10:00 1970 ID is 2
2021-11-28 19:56:01.936 D/DBINFO: Mary Belinda Allway Date of Birth is Mon Jan 12 00:15:21 GMT+10:00 1970 ID is 4
2021-11-28 19:56:01.937 D/DBINFO: Stephen Colin Cobbs Date of Birth is Tue Jan 06 14:01:55 GMT+10:00 1970 ID is 6
2021-11-28 19:56:01.937 D/DBINFO: Trevor Arthur Frankston Date of Birth is Sat Jan 10 03:47:02 GMT+10:00 1970 ID is 8
2021-11-28 19:56:01.937 D/DBINFO: Uriah Stanley Jefferson Date of Birth is Mon Dec 29 19:11:31 GMT+10:00 1969 ID is 10
2021-11-28 19:56:01.937 D/DBINFO: Vladimir Oscar Whitworth Date of Birth is Sat Jan 10 00:29:45 GMT+10:00 1970 ID is 12
2021-11-28 19:56:01.937 D/DBINFO: Company is Dextronics Location is Slough, Berkshire, England ID is 2
Notes:
2021-11-28 19:56:01.937 D/DBINFO: Robert John Smith Date of Birth is Sat Dec 27 17:46:33 GMT+10:00 1969 ID is 1
2021-11-28 19:56:01.938 D/DBINFO: Andrea Susan Stewart Date of Birth is Mon Jan 05 04:56:09 GMT+10:00 1970 ID is 3
2021-11-28 19:56:01.938 D/DBINFO: Lisa Elizabeth Brooks Date of Birth is Sat Jan 03 03:51:21 GMT+10:00 1970 ID is 5
2021-11-28 19:56:01.938 D/DBINFO: Breane Cath Davidson Date of Birth is Thu Jan 01 22:30:14 GMT+10:00 1970 ID is 7
2021-11-28 19:56:01.938 D/DBINFO: George Howard Erksine Date of Birth is Sun Jan 11 00:47:02 GMT+10:00 1970 ID is 9
版本 2.3.0-alpha03 Room 有一个 prepackagedDatabaseCallback 上面写着：-
-
This callback will be invoked after the pre-package DB is copied but before Room had a chance to open it and therefore before the RoomDatabase.Callback methods are invoked. This callback can be useful for updating the pre-package DB schema to satisfy Room's schema validation.
那么我如何使用它来规避无效架构 expected .... found ....?
我可以用这个来介绍触发器吗，因为房间没有创建触发器的注释？
So how could I uses this to circumvent the Invalid Schema expected .... found ....?
以下虽然冗长，但显示了相应更正架构的示例。
Could I use this to introduce Triggers, as room doesn't have annotations for the creation of triggers?
是的，虽然这还没有实际测试过，但这个例子是为了创建触发器。
对示例重新评分的注释 首先，应该注意的是，当最初查看回调时存在问题。这些问题现已得到解决 但是 需要 2.4.0-beta02 或更高版本。问题是：-
- 不允许预打包数据库中的版本 0（通常是这种情况）
- 空数据库传递给 PrePackagedDatabaseCallback
- PrePackagedDatabaseCallback 中应用的数据库更新Lost/Undone
应用的修复
-
Correctly open pre-package database during PrepackagedDatabaseCallback invocation.
-
The actual pre-package database was not being opened because only the file name was being used when creating the temporary open helper instead of the full path. The framework open helper will only open an existing file if the name of the database is a path (starts with '/') otherwise it create a new file. This changes fixes it by using the absolute file path as name.
流
当控制传递给回调时，资产数据库已被复制。因此，从理论上讲，这只是更改 TABLES 和 VIEWS（如果有的话）以匹配房间期望的架构的问题。
经常尝试将房间的期望与房间的发现相匹配会让一些人感到沮丧。下面的示例将克服 minor/small/often 遗漏的问题。它的工作原理是：-
- 删除除 table 之外的所有非 sqlite 或非 android 组件（即来自复制资产数据库的视图、索引和触发器），
- 重命名 tables 以允许创建房间期望的那些，
- 正在使用 Room 的预期架构创建新的 tables，
- 从 Room 生成的 java 复制而来[=146=]
- 正在将重命名的（资产）table 中的数据复制到新创建的 table 中
- INSERT OR IGNORE已经被使用所以约束冲突，比如NOT NULL, UNIQUE, CHECK不会导致异常（把
INSERT OR IGNORE改成INSERT会失败）
- INSERT OR IGNORE已经被使用所以约束冲突，比如NOT NULL, UNIQUE, CHECK不会导致异常（把
- 创建 Room 期望的其他组件（视图、索引和触发器（注意 Room 只有 FTS tables 的触发器））。
- 删除现在多余的重命名 tables
- 正在执行 VACUUM 清理数据库，
- 最后添加任何触发器。
确实希望源（资产）的列顺序正确，空值不包含在具有 NOT NULL 约束的列中。但是，由于使用了 INSERT OR IGNORE，因此不会插入此类行而不是导致异常。
除了从生成的 java 中复制代码外，该过程是自动化的，无需修改即可处理 most/many 资产。
代码
绝大部分代码在@Database class OtherDatabase 中。请注意，这应该可以通过一些调整来应对许多数据库 （请参阅要进行的更改的注释）:-
@SuppressLint({"Range"}) /*<<<<< used due to bug/issue with getColumnIndex introduced with SDK 31 */
@Database(
entities = {Person.class, Company.class, CompanyPersonMap.class}, //<<<<< CHANGED ACCORDINGLY
version = OtherDatabase.DATABASE_VERSION, /* note due to shared usage of DBVERSION OtherDatabase used <<<<< CHANGE ACCORDINGLY */
exportSchema = false /* change to suit */
)
@TypeConverters({AllTypeConverters.class})
abstract class OtherDatabase extends RoomDatabase {
public static final String DATABASE_NAME = "otherprepackageddatabasecallbacktest.db"; //<<<<< CHANGE AS REQUIRED
public static final int DATABASE_VERSION = 1; //<<<<< CHANGE AS REQUIRED
public static final String ASSET_FILE_NAME = "prepackageddatabasecallbacktest.db"; //<<<<< CHANGED AS REQUIRED
/**
* sqlite_master table and column names !!!!!DO NOT CHANGE!!!!!
*/
private static final String SQLITE_MASTER_TABLE_NAME = "sqlite_master";
private static final String SQLITE_MASTER_COL_NAME = "name";
private static final String SQLITE_MASTER_COL_TYPE = "type";
private static final String SQLITE_MASTER_COL_TABLE_NAME = "tbl_name";
private static final String SQLITE_MASTER_COL_SQL = "sql";
abstract AllDao getAllDao(); //<<<<< CHANGE ACCORDINGLY
private static volatile OtherDatabase instance = null; //<<<<< CHANGE ACCORDINGLY
public static OtherDatabase /*<<<< CHANGE ACCORDINGLY */ getInstance(Context context) {
if (instance == null) {
instance = Room.databaseBuilder(context, OtherDatabase.class, OtherDatabase.DATABASE_NAME)
.allowMainThreadQueries() /*<<<<< USED FOR BREVITY CONVENIENCE */
.createFromAsset(ASSET_FILE_NAME, prePkgDbCallback) /* 2nd parameter is the THE CALL BACK to invoke */
.build();
}
return instance;
}
/* THE CALLBACK */
static final PrepackagedDatabaseCallback prePkgDbCallback = new PrepackagedDatabaseCallback() {
final static String assetTablePrefix = "asset_"; /* prefix used for renamed tables - should not need to be changed */
private List<SQLiteMasterComponent> sqLiteMasterComponentArray; /* store for sqlite_master extract */
@Override
public void onOpenPrepackagedDatabase(@NonNull SupportSQLiteDatabase db) {
super.onOpenPrepackagedDatabase(db);
sqLiteMasterComponentArray = buildComponentsList(db); /* gets relevant rows from sqlite_master */
dropNonTableComponents(sqLiteMasterComponentArray,db); /* everything except the tables */
renameTableComponents(sqLiteMasterComponentArray, assetTablePrefix,db); /* rename the tables using prefix */
/*<<<<< TAILOR (the db.execSQL's below) AS APPROPRIATE - SEE COMMENTS THAT FOLLOW >>>>>*/
/* copied from the @Database classes generated java e.g. leave indexes till later
_db.execSQL("CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`))");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_firstName` ON `Person` (`firstName`)");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_lastName` ON `Person` (`lastName`)");
_db.execSQL("CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))");
_db.execSQL("CREATE TABLE IF NOT EXISTS `company_person_map` (`companyid_map` INTEGER NOT NULL, `personid_map` INTEGER NOT NULL, PRIMARY KEY(`companyid_map`, `personid_map`), FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE , FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )");
_db.execSQL("CREATE INDEX IF NOT EXISTS `index_company_person_map_personid_map` ON `company_person_map` (`personid_map`)");
*/
/* Create the tables as per Room definitions - ***** CREATE TABLES COPIED FROM GENERATED JAVA *****
only indexes, views, triggers (for FTS) should be done after the data has been copied so :-
data is loaded faster as no index updates are required.
triggers don't get triggered when loading the data which could result in unexpected results
*/
db.execSQL("CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`));");
db.execSQL("CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))");
db.execSQL("CREATE TABLE IF NOT EXISTS `company_person_map` (`companyid_map` INTEGER NOT NULL, `personid_map` INTEGER NOT NULL, PRIMARY KEY(`companyid_map`, `personid_map`), FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE , FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )");
copyData(sqLiteMasterComponentArray, assetTablePrefix,db); /* copy the data from the renamed asset tables to the newly created Room tables */
/* Create the other Room components - ***** CREATE ? COPIED FROM GENERATED JAVA *****
Now that data has been copied create other Room components indexes, views and triggers
(triggers would only be for FTS (full text search))
again sourced from generated Java
*/
db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_firstName` ON `Person` (`firstName`)");
db.execSQL("CREATE INDEX IF NOT EXISTS `index_Person_lastName` ON `Person` (`lastName`)");
db.execSQL("CREATE INDEX IF NOT EXISTS `index_company_person_map_personid_map` ON `company_person_map` (`personid_map`)");
dropRenamedTableComponents(sqLiteMasterComponentArray, assetTablePrefix,db); /* done with the renamed tables so drop them */
db.execSQL("VACUUM"); /* cleanup the database */
createTriggers(sqLiteMasterComponentArray,db); /* create any triggers */
}
};
static int dropNonTableComponents(List<SQLiteMasterComponent> components, SupportSQLiteDatabase db) {
int rv = 0;
for(SQLiteMasterComponent c: components) {
if (!c.type.equals("table") ) {
db.execSQL("DROP " + c.type + " IF EXISTS " + c.name);
rv++;
}
}
return rv;
}
static int dropRenamedTableComponents(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
int maxForeignKeyCount = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount > maxForeignKeyCount) {
maxForeignKeyCount = c.foreignKeyCount;
}
}
for (int i= maxForeignKeyCount; i >= 0; i--) {
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount == i) {
db.execSQL("DROP " + c.type + " IF EXISTS " + prefix + c.name);
rv++;
}
}
}
return rv;
}
static int renameTableComponents(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
db.execSQL("PRAGMA foreign_keys = ON"); // Just in case turn foreign keys on
for(SQLiteMasterComponent c: components) {
if (c.type.equals("table")) {
db.execSQL("ALTER TABLE " + c.name + " RENAME TO " + prefix + c.name);
rv++;
}
}
return rv;
}
/*
NOTE tables with fewest Foreign Key definitions done first
NOTE makes an assumption that this will not result in FK conflicts
TODO should really be amended to ensure that a table with FK's is only attempted when all of it's parent tables have been loaded
*/
static int copyData(List<SQLiteMasterComponent> components, String prefix, SupportSQLiteDatabase db) {
int rv = 0;
int maxForeignKeyCount = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount > 0) {
maxForeignKeyCount = c.foreignKeyCount;
}
}
for (int i=0; i <= maxForeignKeyCount; i++) {
for (SQLiteMasterComponent c: components) {
if (c.type.equals("table") && c.foreignKeyCount == i) {
db.execSQL("INSERT OR IGNORE INTO " + c.name + " SELECT * FROM " + prefix + c.name + ";");
rv++;
}
}
}
return rv;
}
static int createTriggers(List<SQLiteMasterComponent> components, SupportSQLiteDatabase db) {
int rv = 0;
for (SQLiteMasterComponent c: components) {
if (c.type.equals("trigger")) {
//TODO should really check if the sql includes IF NOT EXISTSand if not add IF NOT EXISTS
db.execSQL(c.sql);
rv++;
}
}
return rv;
}
/**
* Build the list of required SQLiteMasterComponents to save having to access
* sqlite_master many times.
* @param db the SupportSQliteDatabase to access
* @return the list of SQliteMasterComponents extracted
*/
@SuppressLint("Range")
static List<SQLiteMasterComponent> buildComponentsList(SupportSQLiteDatabase db) {
final String FOREIGN_KEY_FLAG_COLUMN = "foreign_key_flag";
ArrayList<SQLiteMasterComponent> rv = new ArrayList<>();
Cursor csr = db.query("SELECT *," +
/* Column to indicate wherther or not FK constraints appear to have been defined
* NOTE!! can be fooled
* e.g. if a column is defined as `my badly named FOREIGN KEY column ` ....
* */
"(" +
"instr(" + SQLITE_MASTER_COL_SQL + ",'FOREIGN KEY') > 0) + " +
"(instr(" + SQLITE_MASTER_COL_SQL + ",' REFERENCES ')> 0) " +
"AS " + FOREIGN_KEY_FLAG_COLUMN + " " +
"FROM " + SQLITE_MASTER_TABLE_NAME + " " +
/* do not want any sqlite tables or android tables included */
"WHERE lower(" + SQLITE_MASTER_COL_NAME + ") NOT LIKE 'sqlite_%' AND lower(" + SQLITE_MASTER_COL_NAME + ") NOT LIKE 'android_%'");
while (csr.moveToNext()) {
SQLiteMasterComponent component = new SQLiteMasterComponent(
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_NAME)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_TYPE)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_TABLE_NAME)),
csr.getString(csr.getColumnIndex(SQLITE_MASTER_COL_SQL)),
csr.getInt(csr.getColumnIndex(FOREIGN_KEY_FLAG_COLUMN)),
0);
if (csr.getInt(csr.getColumnIndex(FOREIGN_KEY_FLAG_COLUMN)) > 0) {
component.foreignKeyCount = component.getForeignKeyCount(db);
}
rv.add(component);
}
csr.close();
return (List<SQLiteMasterComponent>) rv;
}
/**
* Class to hold a row from sqlite_master
*/
private static class SQLiteMasterComponent {
private String name;
private String type;
private String owningTable;
private String sql;
private int foreignKeyFlag = 0;
private int foreignKeyCount = 0;
SQLiteMasterComponent(String name, String type, String owningTable, String sql, int foreignKeyFlag, int foreignKeyCount) {
this.name = name;
this.type = type;
this.owningTable = owningTable;
this.sql = sql;
this.foreignKeyFlag = foreignKeyFlag;
this.foreignKeyCount = foreignKeyCount;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public String getOwningTable() {
return owningTable;
}
public void setOwningTable(String owningTable) {
this.owningTable = owningTable;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
public int getForeignKeyFlag() {
return foreignKeyFlag;
}
public void setForeignKeyFlag(int foreignKeyFlag) {
this.foreignKeyFlag = foreignKeyFlag;
}
public boolean isForeignKey() {
return this.foreignKeyFlag > 0;
}
public int getForeignKeyCount() {
return foreignKeyCount;
}
public void setForeignKeyCount(int foreignKeyCount) {
this.foreignKeyCount = foreignKeyCount;
}
/**
* Retrieve the number of rows returned by PRAGMA foreign_key_list
* @param db The SupportSQLiteDatabase to access
* @return The number of rows i.e. number of Foreign Key constraints
*/
private int getForeignKeyCount(SupportSQLiteDatabase db) {
int rv =0;
Cursor csr = db.query("SELECT count(*) FROM pragma_foreign_key_list('" + this.name + "');");
if (csr.moveToFirst()) {
rv = csr.getInt(0);
}
csr.close();
return rv;
}
}
}
工作示例
资产数据库
资产数据库包含3个tables，person，company and company_person_map
人 DDL是
CREATE TABLE person (personid INTEGER PRIMARY KEY, firstName TEXT, lastName TEXT, middleNames TEXT, dateOfBirth DATE);
预计房间：-
CREATE TABLE IF NOT EXISTS `Person` (`personid` INTEGER, `firstName` TEXT, `lastName` TEXT, `middleNames` TEXT, `dateOfBirth` INTEGER, PRIMARY KEY(`personid`))
- 注意 dateOfBirth 列的 DATE v INTEGER 的类型，房间不接受所以 预期...找到....
公司 DDL 是
CREATE TABLE company (companyid INTEGER PRIMARY KEY, companyName TEXT, city TEXT, state TEXT, country TEXT, notes TEXT);
预计房间：-
CREATE TABLE IF NOT EXISTS `company` (`companyid` INTEGER, `companyName` TEXT, `city` TEXT, `state` TEXT, `country` TEXT, `notes` TEXT, PRIMARY KEY(`companyid`))
- 两者都是可比的房间会接受
company_person_map DDL是
CREATE TABLE company_person_map (
companyid_map INTEGER NOT NULL REFERENCES company(companyid) ON DELETE CASCADE ON UPDATE CASCADE,
personid_map INTEGER NOT NULL REFERENCES person(personid) ON DELETE CASCADE ON UPDATE CASCADE,
PRIMARY KEY (companyid_map, personid_map));
预计房间：-
CREATE TABLE IF NOT EXISTS `company_person_map` (
`companyid_map` INTEGER NOT NULL,`personid_map` INTEGER NOT NULL,
PRIMARY KEY(`companyid_map`, `personid_map`),
FOREIGN KEY(`companyid_map`) REFERENCES `company`(`companyid`) ON UPDATE CASCADE ON DELETE CASCADE ,
FOREIGN KEY(`personid_map`) REFERENCES `Person`(`personid`) ON UPDATE CASCADE ON DELETE CASCADE )
- 虽然差别很大，但有可比性，房间可以接受
资产table包含以下数据：-
人
公司
company_person_map
- 人员 11 未映射到公司。
AllDao是
- none 的插入被使用，也不是所有的查询。
调用 Activity 是 :-
public class MainActivity extends AppCompatActivity {
OtherDatabase dbOther;
AllDao daoOther;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbOther = OtherDatabase.getInstance(this);
daoOther = dbOther.getAllDao();
for(Person p: daoOther.getAllPeople()) {
Log.d("DBINFO",
"Person is " + p.firstName
+ " " + p.middleNames
+ " " + p.lastName
+ " Date of Birth is " + p.dateOfBirth
+ " ID is " + p.id
);
}
for(CompanyWithPeople cwp: dao.getCompanyWithPeople()) {
logCompany(cwp.company,"DBINFO","");
for(Person p: cwp.person) {
logPerson(p,"DBINFO","\n\t");
}
}
}
void logCompany(Company c, String tag, String lineFeed) {
Log.d(tag,lineFeed + "Company is " + c.companyName
+ " Location is " + c.city + ", " + c.state + ", " + c.country
+ " ID is " + c.companyId
+ "\n\t Notes: " + c.notes
);
}
void logPerson(Person p, String tag, String lineFeed) {
Log.d(tag, lineFeed + p.firstName + " " + p.middleNames
+ " " + p.lastName + " Date of Birth is " + p.dateOfBirth
+ " ID is " + p.id
);
}
}
结果
2021-11-28 19:56:01.928 D/DBINFO: Person is Robert John Smith Date of Birth is Sat Dec 27 17:46:33 GMT+10:00 1969 ID is 1
2021-11-28 19:56:01.929 D/DBINFO: Person is Julie Mary Armstrong Date of Birth is Mon Jan 12 23:22:04 GMT+10:00 1970 ID is 2
2021-11-28 19:56:01.929 D/DBINFO: Person is Andrea Susan Stewart Date of Birth is Mon Jan 05 04:56:09 GMT+10:00 1970 ID is 3
2021-11-28 19:56:01.929 D/DBINFO: Person is Mary Belinda Allway Date of Birth is Mon Jan 12 00:15:21 GMT+10:00 1970 ID is 4
2021-11-28 19:56:01.929 D/DBINFO: Person is Lisa Elizabeth Brooks Date of Birth is Sat Jan 03 03:51:21 GMT+10:00 1970 ID is 5
2021-11-28 19:56:01.930 D/DBINFO: Person is Stephen Colin Cobbs Date of Birth is Tue Jan 06 14:01:55 GMT+10:00 1970 ID is 6
2021-11-28 19:56:01.930 D/DBINFO: Person is Breane Cath Davidson Date of Birth is Thu Jan 01 22:30:14 GMT+10:00 1970 ID is 7
2021-11-28 19:56:01.930 D/DBINFO: Person is Trevor Arthur Frankston Date of Birth is Sat Jan 10 03:47:02 GMT+10:00 1970 ID is 8
2021-11-28 19:56:01.930 D/DBINFO: Person is George Howard Erksine Date of Birth is Sun Jan 11 00:47:02 GMT+10:00 1970 ID is 9
2021-11-28 19:56:01.930 D/DBINFO: Person is Uriah Stanley Jefferson Date of Birth is Mon Dec 29 19:11:31 GMT+10:00 1969 ID is 10
2021-11-28 19:56:01.931 D/DBINFO: Person is Valerie Alana Singleton Date of Birth is Thu Jan 01 11:45:07 GMT+10:00 1970 ID is 11
2021-11-28 19:56:01.931 D/DBINFO: Person is Vladimir Oscar Whitworth Date of Birth is Sat Jan 10 00:29:45 GMT+10:00 1970 ID is 12
2021-11-28 19:56:01.936 D/DBINFO: Company is Allbright Construction Location is Sydney, NSW, Australia ID is 1
Notes:
2021-11-28 19:56:01.936 D/DBINFO: Julie Mary Armstrong Date of Birth is Mon Jan 12 23:22:04 GMT+10:00 1970 ID is 2
2021-11-28 19:56:01.936 D/DBINFO: Mary Belinda Allway Date of Birth is Mon Jan 12 00:15:21 GMT+10:00 1970 ID is 4
2021-11-28 19:56:01.937 D/DBINFO: Stephen Colin Cobbs Date of Birth is Tue Jan 06 14:01:55 GMT+10:00 1970 ID is 6
2021-11-28 19:56:01.937 D/DBINFO: Trevor Arthur Frankston Date of Birth is Sat Jan 10 03:47:02 GMT+10:00 1970 ID is 8
2021-11-28 19:56:01.937 D/DBINFO: Uriah Stanley Jefferson Date of Birth is Mon Dec 29 19:11:31 GMT+10:00 1969 ID is 10
2021-11-28 19:56:01.937 D/DBINFO: Vladimir Oscar Whitworth Date of Birth is Sat Jan 10 00:29:45 GMT+10:00 1970 ID is 12
2021-11-28 19:56:01.937 D/DBINFO: Company is Dextronics Location is Slough, Berkshire, England ID is 2
Notes:
2021-11-28 19:56:01.937 D/DBINFO: Robert John Smith Date of Birth is Sat Dec 27 17:46:33 GMT+10:00 1969 ID is 1
2021-11-28 19:56:01.938 D/DBINFO: Andrea Susan Stewart Date of Birth is Mon Jan 05 04:56:09 GMT+10:00 1970 ID is 3
2021-11-28 19:56:01.938 D/DBINFO: Lisa Elizabeth Brooks Date of Birth is Sat Jan 03 03:51:21 GMT+10:00 1970 ID is 5
2021-11-28 19:56:01.938 D/DBINFO: Breane Cath Davidson Date of Birth is Thu Jan 01 22:30:14 GMT+10:00 1970 ID is 7
2021-11-28 19:56:01.938 D/DBINFO: George Howard Erksine Date of Birth is Sun Jan 11 00:47:02 GMT+10:00 1970 ID is 9