kafka-streams/lib/actions/LastState.js

kafka-streams for Node.js

"use strict";

const Promise = require("bluebird");

/**
 * used to hold the last state of key values
 * in a stream e.g. building KTables
 */
class LastState {

    constructor(storage, key = "key", fieldName = "value") {
        this.storage = storage;
        this.key = key;
        this.fieldName = fieldName;
    }

    execute(element) {

        if (!element || typeof element[this.key] === "undefined") {
            return Promise.resolve(element);
        }

        return this.storage.set(element[this.key], element[this.fieldName]).then(value => {
            return element;
        });
    }
}

module.exports = LastState;