Question
Answer and Explanation
In the Orion Context Broker, the modification date of an entity is represented by the dateModified attribute. This attribute is automatically managed by the broker and reflects the last time the entity's attributes were updated.
Here's a breakdown of how it works:
1. Automatic Management: The dateModified attribute is not something you manually set. The Orion Context Broker updates it whenever an entity's attributes are modified through a successful update operation (e.g., using the /v2/entities/{entityId}/attrs endpoint).
2. Format: The dateModified attribute is typically represented as an ISO 8601 timestamp string. For example: "2024-07-26T10:00:00.000Z". This format includes the date, time, and timezone information (usually UTC).
3. Retrieving the Modification Date: You can retrieve the dateModified attribute when querying an entity. When you request an entity using the /v2/entities/{entityId} endpoint, the response will include the dateModified field along with the entity's attributes.
4. Example Response:
{
"id": "urn:ngsi-ld:Device:001",
"type": "Device",
"temperature": {
"value": 25,
"type": "Number"
},
"dateModified": "2024-07-26T10:00:00.000Z"
}
5. Use Cases: The dateModified attribute is useful for various purposes, such as:
- Change Tracking: Monitoring when an entity's data was last updated.
- Data Synchronization: Ensuring that data is synchronized between different systems by comparing modification dates.
- Caching: Implementing caching mechanisms based on the last modification time.
6. Important Note: The dateModified attribute only reflects changes to the entity's attributes. If the entity's metadata (e.g., the entity's type or ID) is changed, it might not update the dateModified attribute. It is primarily for tracking attribute modifications.
In summary, the dateModified attribute in the Orion Context Broker provides a reliable way to track when an entity's attributes were last modified, which is crucial for various data management and synchronization tasks.