RDB Development
When to Use
A relational database (RDB) store allows you to manage local data with or without native SQL statements based on SQLite.
Available APIs
Most of the RDB store APIs are asynchronous interfaces, which can use a callback or promise to return the result. This document uses the promise-based APIs as an example. For details about the APIs, see Relational Database.
Creating or Deleting an RDB Store
The following table describes the APIs available for creating and deleting an RDB store.
Table 1 APIs for creating and deleting an RDB store
API | Description |
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getRdbStore(config: StoreConfig, version: number): Promise<RdbStore> | Obtains an RDB store. This API uses a promise to return the result. You can set parameters for the RDB store based on service requirements and call APIs to perform data operations. - config: configuration of the RDB store. - version: version of the RDB store. |
deleteRdbStore(name: string): Promise<void> | Deletes an RDB store. This API uses a promise to return the result. - name: name of the RDB store to delete. |
Managing Data in an RDB Store
The RDB module provides APIs for inserting, deleting, updating, and querying data in a local RDB store.
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Inserting Data
The RDB module provides APIs for inserting data through a ValuesBucket in a data table. If the data is inserted, the row ID of the data inserted will be returned; otherwise, -1 will be returned.
Table 2 API for inserting data
Class | API | Description |
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RdbStore | insert(name: string, values: ValuesBucket): Promise<number> | Inserts a row of data into a table. This API uses a promise to return the result. If the operation is successful, the row ID will be returned; otherwise, -1 will be returned. - name: name of the target table. - values: data to be inserted into the table. |
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Updating Data
Call the update() method to pass new data and specify the update conditions by using RdbPredicates. If the data is updated, the number of rows of the updated data will be returned; otherwise, 0 will be returned.
Table 3 API for updating data
Class | API | Description |
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RdbStore | update(values: ValuesBucket, rdbPredicates: RdbPredicates): Promise<number> | Updates data based on the specified RdbPredicates object. This API uses a promise to return the result. Return value: number of rows updated. - values: data to update, which is stored in ValuesBucket. - rdbPredicates: conditions for updating data. |
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Deleting Data
Call the delete() method to delete data meeting the conditions specified by RdbPredicates. If the data is deleted, the number of rows of the deleted data will be returned; otherwise, 0 will be returned.
Table 4 API for deleting data
Class | API | Description |
---|---|---|
RdbStore | delete(rdbPredicates: RdbPredicates): Promise<number> | Deletes data from the RDB store based on the specified RdbPredicates object. This API uses a promise to return the result. Return value: number of rows updated. - rdbPredicates: conditions for deleting data. |
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Querying data
You can query data in an RDB store in either of the following ways:
- Call the query() method to query data based on the predicates, without passing any SQL statement.
- Run the native SQL statement.
Table 5 APIs for querying data
Class | API | Description |
---|---|---|
RdbStore | query(rdbPredicates: RdbPredicates, columns: Array): Promise<ResultSet> | Queries data from the RDB store based on specified conditions. This API uses a promise to return the result. - rdbPredicates: conditions for querying data. - columns: columns to query. If this parameter is not specified, the query applies to all columns. |
RdbStore | querySql(sql: string, bindArgs?: Array<ValueType>): Promise<ResultSet> | Queries data using the specified SQL statement. This API uses a promise to return the result. - sql: SQL statement. - bindArgs: arguments in the SQL statement. |
Using Predicates
The RDB module provides RdbPredicates for you to set database operation conditions.
The following table lists common predicates. For more information about predicates, see RdbPredicates.
Table 6 APIs for using RDB store predicates
Class | API | Description |
---|---|---|
RdbPredicates | equalTo(field: string, value: ValueType): RdbPredicates | Sets an RdbPredicates object to match the field with data type ValueType and value equal to the specified value. - field: column name in the database table. - value: value to match the RdbPredicates. - RdbPredicates: RdbPredicates object created. |
RdbPredicates | notEqualTo(field: string, value: ValueType): RdbPredicates | Sets an RdbPredicates object to match the field with data type ValueType and value not equal to the specified value. - field: column name in the database table. - value: value to match the RdbPredicates. - RdbPredicates: RdbPredicates object created. |
RdbPredicates | or(): RdbPredicates | Adds the OR condition to the RdbPredicates object. - RdbPredicates: RdbPredicates with the OR condition. |
RdbPredicates | and(): RdbPredicates | Adds the AND condition to the RdbPredicates object. - RdbPredicates: RdbPredicates with the AND condition. |
RdbPredicates | contains(field: string, value: string): RdbPredicats | Sets an RdbPredicates object to match a string that contains the specified value. - field: column name in the database table. - value: value to match the RdbPredicates. - RdbPredicates: RdbPredicates object created. |
Using the Result Set
A result set can be regarded as a row of data in the queried results. It allows you to traverse and access the data you have queried.
For details about how to use result set APIs, see Result Set.
NOTICE
After a result set is used, you must call the close() method to close it explicitly.
Table 7 APIs for using the result set
Class | API | Description |
---|---|---|
ResultSet | goToFirstRow(): boolean | Moves to the first row of the result set. |
ResultSet | getString(columnIndex:number): string | Obtains the value in the form of a string based on the specified column and current row. |
ResultSet | getBlob(columnIndex:number): Uint8Array | Obtains the value in the form of a byte array based on the specified column and the current row. |
ResultSet | getDouble(columnIndex:number): number | Obtains the value in the form of double based on the specified column and current row. |
ResultSet | getLong(columnIndex:number): number | Obtains the value in the form of a long integer based on the specified column and current row. |
ResultSet | close(): void | Closes the result set. |
Setting Distributed Tables
Setting Distributed Tables
Table 8 API for setting distributed tables
Class | API | Description |
---|---|---|
RdbStore | setDistributedTables(tables: Array<string>): Promise<void>; | Sets distributed tables. This API uses a promise to return the result. - tables: names of the distributed tables to set. |
Obtaining the Distributed Table Name for a Remote Device
You can obtain the distributed table name for a remote device based on the local table name. The distributed table name can be used to query the RDB store of the remote device.
Table 9 API for obtaining the distributed table name of a remote device
Class | API | Description |
---|---|---|
RdbStore | obtainDistributedTableName(device: string, table: string): Promise<string>; | Obtains the distributed table name for a remote device based on the local table name. The distributed table name is required when the RDB store of a remote device is queried. - device: remote device. - table: local table name. |
Synchronizing Data Between Devices
Table 10 API for synchronizing data between devices
Class | API | Description |
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RdbStore | sync(mode: SyncMode, predicates: RdbPredicates): Promise<Array<[string, number]>>; | Synchronizes data between devices. This API uses a promise to return the result. - mode: synchronization mode. SYNC_MODE_PUSH means to push data from the local device to a remote device. SYNC_MODE_PULL means to pull data from a remote device to the local device. - predicates: specifies the data and devices to synchronize. - string: device ID. - number: synchronization status of that device. The value 0 indicates a successful synchronization. Other values indicate a synchronization failure. |
Registering an RDB Store Observer
Table 11 API for registering an observer
Class | API | Description |
---|---|---|
RdbStore | on(event: 'dataChange', type: SubscribeType, observer: Callback<Array<string>>): void; | Registers an observer for this RDB store to subscribe to distributed data changes. When data in the RDB store changes, a callback will be invoked to return the data changes. - type: subscription type. SUBSCRIBE_TYPE_REMOTE means to subscribe to remote data changes. - observer: observer that listens for data changes in the RDB store. |
Unregistering an RDB Store Observer
Table 12 API for unregistering an observer
Class | API | Description |
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RdbStore | off(event:'dataChange', type: SubscribeType, observer: Callback<Array<string>>): void; | Unregisters the observer of the specified type for the RDB store. This method uses a callback to return the result. - type: subscription type. SUBSCRIBE_TYPE_REMOTE means to subscribe to remote data changes. - observer: observer to unregister. |
How to Develop
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Create an RDB store.
- Configure the RDB store attributes, including the RDB store name, storage mode, and whether read-only mode is used.
- Initialize the table structure and related data in the RDB store.
- Create an RDB store.
The sample code is as follows:
import data_rdb from '@ohos.data.rdb' const CREATE_TABLE_TEST = "CREATE TABLE IF NOT EXISTS test (" + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "name TEXT NOT NULL, " + "age INTEGER, " + "salary REAL, " + "blobType BLOB)"; const STORE_CONFIG = {name: "rdbstore.db"} data_rdb.getRdbStore(STORE_CONFIG, 1, function (err, rdbStore) { rdbStore.executeSql(CREATE_TABLE_TEST ) console.info('create table done.') })
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Insert data.
- Create a ValuesBucket to store the data you need to insert.
- Call the insert() method to insert data into the RDB store.
The sample code is as follows:
var u8 = new Uint8Array([1, 2, 3]) const valueBucket = {"name": "Tom", "age": 18, "salary": 100.5, "blobType": u8} let insertPromise = rdbStore.insert("test", valueBucket)
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Query data.
- Create an RdbPredicates object to specify query conditions.
- Call the query() method to query data.
- Call the ResultSet() method to obtain the query result.
The sample code is as follows:
let predicates = new data_rdb.RdbPredicates("test"); predicates.equalTo("name", "Tom") let promisequery = rdbStore.query(predicates) promisequery.then((resultSet) => { resultSet.goToFirstRow() const id = resultSet.getLong(resultSet.getColumnIndex("id")) const name = resultSet.getString(resultSet.getColumnIndex("name")) const age = resultSet.getLong(resultSet.getColumnIndex("age")) const salary = resultSet.getDouble(resultSet.getColumnIndex("salary")) const blobType = resultSet.getBlob(resultSet.getColumnIndex("blobType")) resultSet.close() })
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Set the distributed tables to be synchronized.
- Set the distributed tables.
- Check whether the setting is successful.
The sample code is as follows:
let promise = rdbStore.setDistributedTables(["test"]) promise.then(() => { console.info("setDistributedTables success.") }).catch((err) => { console.info("Failed to set distributed tables.") })
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Synchronize data across devices.
- Construct an RdbPredicates object to specify remote devices within the network to be synchronized.
- Call the sync() method to synchronize data.
- Check whether the data synchronization is successful.
The sample code is as follows:
let predicate = new data_rdb.RdbPredicates('test') predicate.inDevices(['12345678abcde']) let promise = rdbStore.sync(rdb.SyncMode.SYNC_MODE_PUSH, predicate) promise.then((result) => { console.log('sync done.') for (let i = 0; i < result.length; i++) { console.log('device=' + result[i][0] + ' status=' + result[i][1]) } }).catch((err) => { console.log('sync failed') })
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Subscribe to distributed data.
- Register an observer to listen for distributed data changes.
- When data in the RDB store changes, a callback will be invoked to return the data changes.
The sample code is as follows:
function storeObserver(devices) { for (let i = 0; i < devices.length; i++) { console.log('device=' + devices[i] + ' data changed') } } try { rdbStore.on('dataChange', rdb.SubscribeType.SUBSCRIBE_TYPE_REMOTE, storeObserver) } catch (err) { console.log('Failed to register observer') }
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Query data across devices.
- Obtain the distributed table name for a remote device based on the local table name.
- Call the ResultSet() method to obtain the query result.
The sample code is as follows:
let tableName = rdbStore.obtainDistributedTableName(deviceId, "test"); let resultSet = rdbStore.querySql("SELECT * FROM " + tableName)