Lightweight storage provides applications with data processing capability and allows applications to perform lightweight data storage and query. Data is stored in key-value (KV) pairs. Keys are of the string type, and values can be of the number, string, or Boolean type.
> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version.
## Modules to Import
```
import data_Preferences from '@ohos.data.preferences'
Removes the singleton **Preferences** instance of the specified file from the memory, and deletes the specified file, its backup file, and corrupted files. After the specified files are deleted, the **Preferences** instance cannot be used for data operations. Otherwise, data inconsistency will occur. This method uses an asynchronous callback to return the execution result.
Removes the singleton **Preferences** instance of the specified file from the memory, and deletes the specified file, its backup file, and corrupted files. After the specified files are deleted, the **Preferences** instance cannot be used for data operations. Otherwise, data inconsistency will occur. This method uses a promise to return the execution result.
Removes the singleton **Preferences** instance of a file from the cache. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
This method uses an asynchronous callback to return the result.
Removes the singleton **Preferences** instance of a file from the cache. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
This method uses an asynchronous callback to return the result.
Obtains the **Preferences** instance corresponding to the specified file, writes data to the **Preferences** instance using a **Preferences** API, and saves data to the file using **flush()** or **flushSync()**.
This method uses an asynchronous callback to return the result.
Obtains the **Preferences** instance corresponding to the specified file, writes data to the **Preferences** instance using a **Preferences** API, and saves data to the file using **flush()** or **flushSync()**.
This method uses an asynchronous callback to return the result.
Lightweight storage provides applications with data processing capability and allows applications to perform lightweight data storage and query. Data is stored in key-value pairs. Keys are of the string type, and values can be of the numeric, string, or Boolean type.
Lightweight storage provides applications with data processing capability and allows applications to perform lightweight data storage and query. Data is stored in key-value (KV) pairs. Keys are of the string type, and values can be of the number, string, or Boolean type.
>The initial APIs of this module are supported since API version 6. Newly added APIs will be marked with a superscript to indicate their earliest API version.
## Modules to Import<a name="s56d19203690d4782bfc74069abb6bd71"></a>
> The initial APIs of this module are supported since API version 6. Newly added APIs will be marked with a superscript to indicate their earliest API version. <br/>The APIs of this module are no longer maintained since API Version 9. You are advised to use [@ohos.data.preferences](js-apis-data-preferences.md).
<tdclass="cellrowborder"valign="top"width="44.519999999999996%"headers="mcps1.1.6.1.5 "><pid="p12478654172415"><aname="p12478654172415"></a><aname="p12478654172415"></a>Maximum length of a key. It is 80 bytes.</p>
<tdclass="cellrowborder"valign="top"width="44.519999999999996%"headers="mcps1.1.6.1.5 "><pid="p1470645211154"><aname="p1470645211154"></a><aname="p1470645211154"></a>Maximum length of a value of the string type. It is 8192 bytes.</p>
<td class="cellrowborder" valign="top" width="49.614822038030226%" headers="mcps1.1.5.1.4 "><p id="p989815213187"><a name="p989815213187"></a><a name="p989815213187"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
import dataStorage from '@ohos.data.storage'
import featureAbility from '@ohos.ability.featureAbility'
(async () => {
var context = featureAbility.getContext()
var path = await context.getFilesDir()
dataStorage.getStorage(path + '/mystore', function (err, storage) {
if (err) {
console.info("Get the storage failed, path: " + path + '/mystore')
return;
}
storage.putSync('startup', 'auto')
storage.flushSync()
})
})()
## dataStorage.getStorage
getStorage(path: string): Promise<Storage>
Reads a file and loads the data to the **Storage** instance. This method uses a promise to return the execution result.
<td class="cellrowborder" valign="top" width="69.56%" headers="mcps1.1.3.1.2 "><p id="p1062005172514"><a name="p1062005172514"></a><a name="p1062005172514"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
import dataStorage from '@ohos.data.storage'
import featureAbility from '@ohos.ability.featureAbility'
(async () => {
var context = featureAbility.getContext()
var path = await context.getFilesDir()
let promise = dataStorage.getStorage(path + '/mystore')
promise.then((storage) => {
storage.putSync('startup', 'auto')
storage.flushSync()
}).catch((err) => {
console.info("Get the storage failed, path: " + path + '/mystore')
})
}()
## dataStorage.deleteStorageSync
deleteStorageSync(path: string): void
Deletes the singleton **Storage** instance of a file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified files are deleted, the **Storage** instance cannot be used for data operations. Otherwise, data inconsistency will occur. This method uses a synchronous mode.
Deletes the singleton **Storage** instance of a file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified files are deleted, the **Storage** instance cannot be used for data operations. Otherwise, data inconsistency will occur. This method uses an asynchronous callback to return the execution result.
Removes the singleton **Storage** instance of the specified file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified file is deleted, the **Storage** instance cannot be used to perform any data operation. Otherwise, data inconsistency will occur. This method uses a synchronous mode.
Removes the singleton **Storage** instance of the specified file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified file is deleted, the **Storage** instance cannot be used to perform any data operation. Otherwise, data inconsistency will occur. This method uses an asynchronous callback to return the execution result.
<td class="cellrowborder" valign="top" width="54.39297903461725%" headers="mcps1.1.5.1.4 "><p id="p396915388374"><a name="p396915388374"></a><a name="p396915388374"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
dataStorage.deleteStorage(path + '/mystore', function (err) {
Removes the singleton **Storage** instance of the specified file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified file is deleted, the **Storage** instance cannot be used to perform any data operation. Otherwise, data inconsistency will occur. This method uses a promise to return the execution result.
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p15446536474"><a name="p15446536474"></a><a name="p15446536474"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = dataStorage.deleteStorage(path + '/mystore')
Removes the singleton **Storage** instance of the specified file from the memory. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
deleteStorage(path: string): Promise<void>
Deletes the singleton **Storage** instance of a file from the memory, and deletes the specified file, its backup file, and damaged files. After the specified files are deleted, the **Storage** instance cannot be used for data operations. Otherwise, data inconsistency will occur. This method uses a promise to return the execution result.
| Promise<void> | Promise used to return the result.|
- Example
```
let promisedelSt = dataStorage.deleteStorage(path + '/mystore')
promisedelSt.then(() => {
console.info("Deleted successfully.")
}).catch((err) => {
console.info("Deleted failed with err: " + err)
})
```
## dataStorage.removeStorageFromCacheSync
removeStorageFromCacheSync(path: string): void
Removes the singleton **Storage** instance of a file from the cache. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
Removes the singleton **Storage** instance of the specified file from the memory. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
<td class="cellrowborder" valign="top" width="52.58898098488542%" headers="mcps1.1.5.1.4 "><p id="p191301575425"><a name="p191301575425"></a><a name="p191301575425"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
dataStorage.removeStorageFromCache(path + '/mystore', function (err) {
if (err) {
console.info("Removed storage from cache failed with err: " + err)
return
}
console.info("Removed storage from cache successfully.")
Removes the singleton **Storage** instance of the specified file from the memory. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p13941645472"><a name="p13941645472"></a><a name="p13941645472"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = dataStorage.removeStorageFromCache(path + '/mystore')
promise.then(() => {
console.info("Removed storage from cache successfully.")
}).catch((err) => {
console.info("Removed storage from cache failed with err: " + err)
Removes the singleton **Storage** instance of a file from the cache. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
This method uses an asynchronous callback to return the result.
Removes the singleton **Storage** instance of a file from the cache. The removed instance cannot be used for data operations. Otherwise, data inconsistency will occur.
This method uses an asynchronous callback to return the result.
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p10404192513199"><a name="p10404192513199"></a><a name="p10404192513199"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p1140502514190"><a name="p1140502514190"></a><a name="p1140502514190"></a>Default value to be returned if the value of the specified key does not exist. The value can be a number, string, or Boolean value.</p>
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p1832294181917"><a name="p1832294181917"></a><a name="p1832294181917"></a>Value corresponding to the specified key. If the value is null or not in the default value format, the default value is returned.</p>
| key | string | Yes| Key of the data. It cannot be empty.|
| defValue | ValueType | Yes| Default value to be returned if the value of the specified key does not exist. It can be a number, string, or Boolean value.|
- Return value
| Type| Description|
| -------- | -------- |
| ValueType | Value corresponding to the specified key. If the value is null or not in the default value format, the default value is returned.|
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p793710294206"><a name="p793710294206"></a><a name="p793710294206"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p129372299204"><a name="p129372299204"></a><a name="p129372299204"></a>Default value to be returned. The value can be a number, string, or Boolean value.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p893812912201"><a name="p893812912201"></a><a name="p893812912201"></a>Callback used to return the result.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p717812534216"><a name="p717812534216"></a><a name="p717812534216"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p817813533210"><a name="p817813533210"></a><a name="p817813533210"></a>Default value to be returned. The value can be a number, string, or Boolean value.</p>
<td class="cellrowborder" valign="top" width="70.41%" headers="mcps1.1.3.1.2 "><p id="p15633101522214"><a name="p15633101522214"></a><a name="p15633101522214"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = storage.get('startup', 'default')
promise.then((value) => {
console.info("The value of startup is " + value)
}).catch((err) => {
console.info("Get the value of startup failed with err: " + err)
})
```
### putSync<a name="section2042914810266"></a>
putSync\(key: string, value: ValueType\): void
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush\(\)** or **flushSync\(\)**.
This method uses an asynchronous callback to return the result.
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p6628521122615"><a name="p6628521122615"></a><a name="p6628521122615"></a>Key of the data to be modified. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p15628721142612"><a name="p15628721142612"></a><a name="p15628721142612"></a>New value. The value can be a number, string, or Boolean value.</p>
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush\(\)** or **flushSync\(\)**.
<td class="cellrowborder" valign="top" width="51.55533885909311%" headers="mcps1.1.5.1.4 "><p id="p775614662815"><a name="p775614662815"></a><a name="p775614662815"></a>Key of the data to be modified. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="51.55533885909311%" headers="mcps1.1.5.1.4 "><p id="p117561246192811"><a name="p117561246192811"></a><a name="p117561246192811"></a>New value. The value can be a number, string, or Boolean value.</p>
<td class="cellrowborder" valign="top" width="51.55533885909311%" headers="mcps1.1.5.1.4 "><p id="p375610463287"><a name="p375610463287"></a><a name="p375610463287"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
storage.put('startup', 'auto', function (err) {
if (err) {
console.info("Put the value of startup failed with err: " + err)
return
}
console.info("Put the value of startup successfully.")
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush\(\)** or **flushSync\(\)**.
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p144354963019"><a name="p144354963019"></a><a name="p144354963019"></a>Key of the data to be modified. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p17435149123016"><a name="p17435149123016"></a><a name="p17435149123016"></a>New value. The value can be a number, string, or Boolean value.</p>
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p208781523143017"><a name="p208781523143017"></a><a name="p208781523143017"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = storage.put('startup', 'auto')
promise.then(() => {
console.info("Put the value of startup successfully.")
}).catch((err) => {
console.info("Put the value of startup failed with err: " + err)
})
```
### hasSync<a name="section7273343143018"></a>
hasSync\(key: string\): boolean
Checks whether the storage object contains data with the specified key.
### putSync
putSync(key: string, value: ValueType): void
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush()** or **flushSync()**.
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p8697139312"><a name="p8697139312"></a><a name="p8697139312"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="48.12286689419795%" headers="mcps1.1.5.1.4 "><p id="p14699746114020"><a name="p14699746114020"></a><a name="p14699746114020"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="48.12286689419795%" headers="mcps1.1.5.1.4 "><p id="p147004466406"><a name="p147004466406"></a><a name="p147004466406"></a>Callback used to return the result.</p>
<td class="cellrowborder" valign="top" width="59.76596782057533%" headers="mcps1.1.5.1.4 "><p id="p1433213456"><a name="p1433213456"></a><a name="p1433213456"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="69.44%" headers="mcps1.1.3.1.2 "><p id="p202076136463"><a name="p202076136463"></a><a name="p202076136463"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = storage.has('startup')
promise.then((isExist) => {
if (isExist) {
console.info("The key of startup is contained.")
}
}).catch((err) => {
console.info("Check the key of startup failed with err: " + err)
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush()** or **flushSync()**.
This method uses an asynchronous callback to return the result.
Obtains the **Storage** instance corresponding to the specified file, writes data to the **Storage** instance using a **Storage** API, and saves the modification using **flush()** or **flushSync()**.
This method uses an asynchronous callback to return the result.
<td class="cellrowborder" valign="top" width="61.29%" headers="mcps1.1.5.1.4 "><p id="p9338731476"><a name="p9338731476"></a><a name="p9338731476"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="51.07752315943442%" headers="mcps1.1.5.1.4 "><p id="p76361658497"><a name="p76361658497"></a><a name="p76361658497"></a>Key of the data. It cannot be empty.</p>
<td class="cellrowborder" valign="top" width="51.07752315943442%" headers="mcps1.1.5.1.4 "><p id="p156361259495"><a name="p156361259495"></a><a name="p156361259495"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
storage.delete('startup', function (err) {
if (err) {
console.info("Delete startup key failed with err: " + err)
return
}
console.info("Deleted startup key successfully.")
})
```
### delete<a name="section11711858125016"></a>
delete\(key: string\): Promise<void\>
Deletes the data with the specified key from this storage object.
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p36981947155117"><a name="p36981947155117"></a><a name="p36981947155117"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = storage.delete('startup')
promise.then(() => {
console.info("Deleted startup key successfully.")
}).catch((err) => {
console.info("Delete startup key failed with err: " + err)
})
```
### flushSync<a name="section1952191618523"></a>
flushSync\(\): void
Saves the modification of the current object to the current **Storage** instance and synchronizes the modification to the file.
<td class="cellrowborder" valign="top" width="53.13505607020965%" headers="mcps1.1.5.1.4 "><p id="p19851715105412"><a name="p19851715105412"></a><a name="p19851715105412"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example
```
let promisedel = storage.delete('startup')
promisedel.then(() => {
console.info("Deleted startup key successfully.")
}).catch((err) => {
console.info("Delete startup key failed with err: " + err)
})
```
### flushSync
flushSync(): void
Saves the modification of this object to the **Storage** instance and synchronizes the modification to the file.
<td class="cellrowborder" valign="top" width="82.99%" headers="mcps1.1.3.1.2 "><p id="p1273364018550"><a name="p1273364018550"></a><a name="p1273364018550"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
### flush
```
let promise = storage.flush()
promise.then(() => {
console.info("Flushed to file successfully.")
}).catch((err) => {
console.info("Flush to file failed with err: " + err)
})
```
flush(): Promise<void>
Saves the modification of this object to the **Storage** instance and synchronizes the modification to the file.
Subscribes to data changes. The **StorageObserver** needs to be implemented. When the value of the key subscribed to is changed, a callback will be invoked after **flush()** or **flushSync()** is executed.
<td class="cellrowborder" valign="top" width="51.32130667966845%" headers="mcps1.1.5.1.4 "><p id="p84590321224"><a name="p84590321224"></a><a name="p84590321224"></a>Callback used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
storage.clear(function (err) {
if (err) {
console.info("Clear to file failed with err: " + err)
<td class="cellrowborder" valign="top" width="79.62%" headers="mcps1.1.3.1.2 "><p id="p1337317471631"><a name="p1337317471631"></a><a name="p1337317471631"></a>Promise used to return the result.</p>
</td>
</tr>
</tbody>
</table>
- Example:
```
let promise = storage.clear()
promise.then(() => {
console.info("Cleared to file successfully.")
}).catch((err) => {
console.info("Clear to file failed with err: " + err)
})
```
### on \('change'\)<a name="section189332511954"></a>
Subscribes to data changes. The **StorageObserver** needs to be implemented. When the value of the key subscribed to is changed, a callback will be invoked after **flush\(\)** or **flushSync\(\)** is executed.
