DatabaseHelper

java.lang.Object
- ohos.data.DatabaseHelper

```
public class DatabaseHelper
extends Object
```
Provides a multi mode-data-access framework to operate application data in databases. A valid context should be passed in so that the database file can be created in the specified path. For more path details, see Context#getDatabaseDir() and Context#getPreferencesDir().
This class provides methods for constructing and deleting ORM, RDB, and Preferences databases. It is the main entry class in the database scenario.

从以下版本开始:

1

SystemCapability

SystemCapability.Data#DATA_APPDATAMGR

构造器概要

构造器
构造器说明

DatabaseHelper(Context context)
A constructor used to create a DatabaseHelper instance based on the specified context.

构造器
构造器	说明
`DatabaseHelper(Context context)`	A constructor used to create a `DatabaseHelper` instance based on the specified context.

方法概要

所有方法静态方法实例方法具体方法
限定符和类型	方法	说明
`boolean`	`deletePreferences(String name)`	Deletes a `Preferences` instance matching a specified preferences file name from the cache which is performed by `DatabaseHelper#removePreferencesFromCache` and deletes the preferences file.
`boolean`	`deleteRdbStore(String name)`	Deletes the database with a specified name.
`boolean`	`deleteRdbStore(DatabaseFileConfig fileConfig)`	Deletes a database with a specified database file configuration.
`OrmContext`	`getOrmContext(String alias)`	Obtains an ORM context mapping to an ORM database with a specified alias.
`<T extends OrmDatabase> OrmContext`	`getOrmContext(String alias, String name, Class<T> ormDatabase, OrmMigration... migrations)`	Creates an object-relational mapping (ORM) database and obtains the context mapped to this database.
`<T extends OrmDatabase> OrmContext`	`getOrmContext(OrmConfig ormConfig, Class<T> ormDatabase, OrmMigration... migrations)`	Creates an object-relational mapping (ORM) database and obtains the `OrmContext` object mapped to the database.
`Preferences`	`getPreferences(String name)`	Obtains a `Preferences` instance matching a specified preferences file name.
`RdbStore`	`getRdbStore(StoreConfig config, int version, RdbOpenCallback openCallback)`	Obtains an RDB store.
`RdbStore`	`getRdbStore(StoreConfig config, int version, RdbOpenCallback openCallback, ResultSetHook resultSetHook)`	Obtains an RDB store.
`boolean`	`moveDatabase(Context srcContext, String srcName, String destName)`	Moves the database.
`boolean`	`movePreferences(Context sourceContext, String sourceName, String targetName)`	Moves the preferences file.
`static int`	`releaseRdbMemory()`	Releases the heap memory in the SQLite database.
`void`	`removePreferencesFromCache(String name)`	Deletes a `Preferences` instance matching a specified preferences file name from the cache.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 构造器详细资料
  - DatabaseHelper
```
public DatabaseHelper(Context context)
```
    A constructor used to create a DatabaseHelper instance based on the specified context.
    The context will also be included in the created DatabaseHelper instance.
    
    参数:
    
    context - Indicates the context Context. The context cannot be null if the database is an encrypted database.
    
    从以下版本开始:
    
    1
- 方法详细资料
  - getRdbStore
```
public RdbStore getRdbStore(StoreConfig config,
                            int version,
                            RdbOpenCallback openCallback)
```
    Obtains an RDB store.
    You can set parameters of the RDB store as required. In general, this method is recommended to obtain a rdb store.
    
    参数:
    
    config - Indicates the configuration of the database related to this RDB store. The configurations include the database path, storage mode, and whether the database is read-only.
    
    version - Indicates the database version for upgrade or downgrade.
    
    openCallback - Indicates a helper used to handle RdbOpenCallback.onCreate(ohos.data.rdb.RdbStore), RdbOpenCallback.onUpgrade(ohos.data.rdb.RdbStore, int, int), RdbOpenCallback.onDowngrade(ohos.data.rdb.RdbStore, int, int) and RdbOpenCallback.onOpen(ohos.data.rdb.RdbStore).
    
    返回:
    
    Returns an RDB store RdbStore.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    从以下版本开始:
    
    3
  - getRdbStore
```
public RdbStore getRdbStore(StoreConfig config,
                            int version,
                            RdbOpenCallback openCallback,
                            ResultSetHook resultSetHook)
```
    Obtains an RDB store.
    You can set parameters of the RDB store as required, and call the related interfaces to perform data operations.
    
    参数:
    
    config - Indicates the configuration of the database related to this RDB store. The configurations include the database path, storage mode, and whether the database is read-only.
    
    version - Indicates the database version for upgrade or downgrade.
    
    openCallback - Indicates a helper used to handle RdbOpenCallback.onCreate(ohos.data.rdb.RdbStore), RdbOpenCallback.onUpgrade(ohos.data.rdb.RdbStore, int, int), RdbOpenCallback.onDowngrade(ohos.data.rdb.RdbStore, int, int) and RdbOpenCallback.onOpen(ohos.data.rdb.RdbStore).
    
    resultSetHook - Indicates a result set factory ResultSetHook.
    
    返回:
    
    Returns an RDB store RdbStore.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    从以下版本开始:
    
    1
  - getOrmContext
```
public <T extends OrmDatabase> OrmContext getOrmContext(String alias,
                                                        String name,
                                                        Class<T> ormDatabase,
                                                        OrmMigration... migrations)
```
    Creates an object-relational mapping (ORM) database and obtains the context mapped to this database.
    You can call this method to add, delete, update, and query data in the ORM database. To delete a database file, call the deleteRdbStore(java.lang.String) method with the database name specified.
    
    类型参数:
    
    T - Indicates an ORM database class that inherits from OrmDatabase.
    
    参数:
    
    alias - Indicates the alias of the ORM database.
    
    name - Indicates the database file name.
    
    ormDatabase - Indicates the ORM database.
    
    migrations - Indicates the configuration instance used for database upgrade and downgrade.
    
    返回:
    
    Returns the context mapped to the ORM database.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    从以下版本开始:
    
    3
  - getOrmContext
```
public <T extends OrmDatabase> OrmContext getOrmContext(OrmConfig ormConfig,
                                                        Class<T> ormDatabase,
                                                        OrmMigration... migrations)
```
    Creates an object-relational mapping (ORM) database and obtains the OrmContext object mapped to the database.
    You can call the OrmContext interface to add, delete, update, and query data in the ORM database. To delete a database file, call the deleteRdbStore(java.lang.String) method with the database file path specified.
    
    类型参数:
    
    T - Indicates an ORM database class that inherits from OrmDatabase.
    
    参数:
    
    ormConfig - Indicates the ORM database configuration.
    
    ormDatabase - Indicates the ORM database used to store data.
    
    migrations - Indicates the ORM database migration callback.
    
    返回:
    
    Returns a OrmContext object.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    从以下版本开始:
    
    3
  - getOrmContext
```
public OrmContext getOrmContext(String alias)
```
    Obtains an ORM context mapping to an ORM database with a specified alias.
    This method applies to an ORM database that has been created.
    
    参数:
    
    alias - Indicates the alias of the ORM database, such as name..
    
    返回:
    
    Returns a OrmContext object.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    从以下版本开始:
    
    1
  - deleteRdbStore
```
public boolean deleteRdbStore(String name)
```
    Deletes the database with a specified name.
    
    参数:
    
    name - Indicates the database name.
    
    返回:
    
    Returns true if the database is deleted; returns false otherwise.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if the passed name or path is invalid, or a relative path is passed.
    
    从以下版本开始:
    
    3
  - deleteRdbStore
```
public boolean deleteRdbStore(DatabaseFileConfig fileConfig)
```
    Deletes a database with a specified database file configuration.
    
    参数:
    
    fileConfig - Indicates the database file configuration.
    
    返回:
    
    Returns true if the database is successfully deleted; returns false otherwise.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if fileConfig is invalid.
    
    从以下版本开始:
    
    4
  - releaseRdbMemory
```
public static int releaseRdbMemory()
```
    Releases the heap memory in the SQLite database.
    This method depends on the sqlite3_release_memory method of the SQLite database, which determines how much heap memory will be released.
    
    返回:
    
    Returns the released heap memory in bytes.
    
    从以下版本开始:
    
    3
  - getPreferences
```
public Preferences getPreferences(String name)
```
    Obtains a Preferences instance matching a specified preferences file name.
    The Preferences instance loads all data of the preferences file and resides in the memory. You can use removePreferencesFromCache(java.lang.String) to remove the instance from the memory.
    
    参数:
    
    name - Indicates the name of preferences file stored in a path specified by Context.getPreferencesDir().
    
    返回:
    
    Returns the Preferences instance matching the specified preferences file name.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if name or Context.getPreferencesDir() is invalid.
    
    从以下版本开始:
    
    1
  - deletePreferences
```
public boolean deletePreferences(String name)
```
    Deletes a Preferences instance matching a specified preferences file name from the cache which is performed by DatabaseHelper#removePreferencesFromCache and deletes the preferences file.
    When deleting the Preferences instance, you must release all references of the instance. In addition, do not use the instance to perform data operations. Otherwise, data inconsistency will occur.
    
    参数:
    
    name - Indicates the name of preferences file stored in a path specified by Context.getPreferencesDir().
    
    返回:
    
    Returns true if the Preferences instance and the preferences file are deleted; returns false otherwise.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if name or Context.getPreferencesDir() is invalid.
    
    从以下版本开始:
    
    1
  - removePreferencesFromCache
```
public void removePreferencesFromCache(String name)
```
    Deletes a Preferences instance matching a specified preferences file name from the cache.
    When deleting the Preferences instance, you must release all references of the instance. In addition, do not use the instance to perform data operations. Otherwise, data inconsistency will occur.
    
    参数:
    
    name - Indicates the name of preferences file stored in a path specified by Context.getPreferencesDir().
    
    抛出:
    
    IllegalArgumentException - Throws this exception if name or Context.getPreferencesDir() is invalid.
    
    从以下版本开始:
    
    1
  - movePreferences
```
public boolean movePreferences(Context sourceContext,
                               String sourceName,
                               String targetName)
```
    Moves the preferences file. The file name can be changed.
    
    参数:
    
    sourceContext - Indicates the context used to obtain the path of the source file.
    
    sourceName - Indicates the source file name.
    
    targetName - Indicates the target file name. The file path can be obtained using the Context of this DatabaseHelper instance.
    
    返回:
    
    Returns true if the preferences file is moved successfully; returns false otherwise.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    IllegalStateException - Throws this exception if an error occurs during the file move.
    
    从以下版本开始:
    
    3
  - moveDatabase
```
public boolean moveDatabase(Context srcContext,
                            String srcName,
                            String destName)
```
    Moves the database. The database name can be changed.
    
    参数:
    
    srcContext - Indicates the context used to obtain the path of the source database.
    
    srcName - Identifies the source database. It can be the database name, in which case the database path can be obtained using srcContext. It can also be the absolute path of the source database, for example, /xxx/xxx/xxx. In this case, srcContext can be null.
    
    destName - Indicates the target database name.
    
    返回:
    
    Returns true if the database is moved successfully; returns false otherwise.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if any of the input parameters is invalid.
    
    IllegalStateException - Throws this exception if an error occurs during the database move.
    
    从以下版本开始:
    
    3

类 DatabaseHelper

构造器概要

方法概要

从类继承的方法 java.lang.Object

构造器详细资料

DatabaseHelper

方法详细资料

getRdbStore

getRdbStore

getOrmContext

getOrmContext

getOrmContext

deleteRdbStore

deleteRdbStore

releaseRdbMemory

getPreferences

deletePreferences

removePreferencesFromCache

movePreferences

moveDatabase