Managing Internal State Example

In this example, we are creating an app that records the number of messages sent on the server using the Persistence object.

To store the message count, we can write an executePostMessageSent event handler as shown below:

public async executePostMessageSent(message: IMessage, read: IRead, http: IHttp, persistence: IPersistence, modify: IModify): Promise<void> {
    //create a new association to count messages
    const association = new RocketChatAssociationRecord(RocketChatAssociationModel.MISC, 'message-count');
    const persis = read.getPersistenceReader();
    try {
        const record = await persis.readByAssociation(association) as RecordItem[];
        let count = 0;

        if (record.length > 0) {
            count = record[0].count;
            this.getLogger().log(`Current count: ${count}`);
        }
        count ++;
        await persistence.updateByAssociation(association, { count }, true);

        //log the number of messages
        this.getLogger().log(`Updated Message Sent Count: ${count}`);
    } catch (err) {
        this.getLogger().error(err);
    }
}

Here,

• The count variable temporarily stores the number of messages sent. It is initialized to zero and updated based on data retrieved from persistent storage.

• When the executePostMessageSent handler is called, it retrieves the current message count using the readByAssociation method. If a record exists, the count variable is updated accordingly.

• Next, the count is incremented by one to account for the newly sent message. Finally, the updated count is saved back to persistent storage using the updateByAssociation method, ensuring the count is preserved across different handler executions.

In this way, even in a cluster environment, your app in each Rocket.Chat instance can share data from a single data source, the Rocket.Chat persistence storage and maintain data consistency. Check the full demo for more details!