sqmicro-connection/src/record-formatter.js

Connection abstraction for SQ Micro.

const { Transform } = require('stream');
const Private = Symbol['Private'];

const RECORD_TERMINATOR = '\n';
const DEFAULT_DELIMITER = '|';
const EMPTY_VALUE = '';

/**
 * Поток преобразования сущностей в строки. Ожидает на входе объекты вида
 * `{ row: object, fields: Array<string> }`. На выходе - строка. Например:
 * @example
 * // на входе:
 * const data = {
 *      row: { a: 1, c: 2 },
 *      fields: ['a', 'b', 'c']
 * };
 * // на выходе (delimiter: '|'):
 * const res = '1||2\n';
 * @param {object} [options]
 * @param {string} [options.delimiter=|] символ-разделитель полей.
 */
module.exports = class RecordFormatter extends Transform {
    constructor(options = {}) {
        super({
            objectMode: true
        });

        this[Private] = {
            delimiter: getDelimiter(options),
            fieldNames: getFieldNames(options)
        };
    }

    _transform(row, _, cb) {
        const pvt = this[Private];

        const record = pvt.fieldNames
            .map(field => JSON.stringify(row[field]) || EMPTY_VALUE)
            .join(pvt.delimiter)
            + RECORD_TERMINATOR;
        
        this.push(record);
        
        cb();
    }
}

function getDelimiter(options) {
    const delimiter = options.delimiter || DEFAULT_DELIMITER;
    
    // delimiter should be compatible with any driver
    if (typeof(delimiter) !== 'string' || delimiter.length !== 1) {
        throw Error(`Delimiter must be a single character`);
    }

    // \n is record terminator (pg does not support another one).
    if (delimiter === '\n') {
        throw Error(`Delimiter should not be a new line symbol '\\n'.`)
    }

    return delimiter;
}

function getFieldNames(options) {
    if (!options || !Array.isArray(options.fieldNames) || options.fieldNames.length < 1) {
        throw Error(`options.fieldNames shoupd be a non-empty array of strings`);
    }

    return options.fieldNames;
}