harmony 鸿蒙Data Management Development

2022-10-28
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Data Management Development

How Do I Save PixelMap Data to a Database?

Applicable to: OpenHarmony SDK 3.2.3.5

You can convert a PixelMap into an ArrayBuffer and save the ArrayBuffer to your database.

How Do I Obtain RDB Store Files?

Applicable to: OpenHarmony SDK 3.2.3.5, stage model of API version 9

Run the hdc_std command to copy the .db, .db-shm, and .db-wal files in /data/app/el2/100/database/bundleName/entry/db/, and then use the SQLite tool to open the files.

Example:

 hdc_std file recv /data/app/el2/100/database/com.xxxx.xxxx/entry/db/test.db ./test.db

Does the Database Has a Lock Mechanism?

Applicable to: OpenHarmony SDK 3.2.5.5, stage model of API version 9

The distributed data service (DDS), relational database (RDB) store, and preferences provided OpenHarmony have a lock mechanism. You do not need to bother with the lock mechanism during the development.

What Is a Transaction in an RDB Store?

Applicable to: all versions

When a large number of operations are performed in an RDB store, an unexpected exception may cause a failure of some data operations and loss of certain data. As a result, the application may become abnormal or even crash.

A transaction is a group of tasks serving as a single logical unit. It eliminates the failure of some of the operations and loss of associated data.

What Data Types Does an RDB Store Support?

Applicable to: OpenHarmony SDK 3.0 or later, stage model of API version 9

An RDB store supports data of the number, string, and Boolean types. The number array supports data of the Double, Long, Float, Int, or Int64 type, with a maximum precision of 17 decimal digits.

How Do I View Database db Files?

Applicable to: OpenHarmony SDK 3.2.6.5, stage model of API version 9

Run the hdc_std shell command.
Obtain the absolute path or sandbox path of the database.

The absolute path is /data/app/el2//database/. The default is 100.

To obtain the sandbox path, run the ps -ef|grep hapName command to obtain the process ID of the application.

The database sandbox path is /proc//root/data/storage/el2/database/.

Run the find ./ -name “*.db” command in the absolute path or sandbox path of the database.

How Do I Store Long Text Data?

Applicable to: OpenHarmony SDK 3.2.5.5, API version 9

Preferences support a string of up to 8192 bytes.
The KV store supports a value of up to 4 MB.

Reference: Preference Overview and Distributed Data Service Overview

How Do I Develop DataShare on the Stage Model

Applicable to: OpenHarmony SDK 3.2.5.5, API version 9

The DataShare on the stage model cannot be used with the DataAbility for the FA model. The connected server application must be implemented by using DataShareExtensionAbility.

Reference: DataShare Development