mysql-queue-pool/lib/queue.js

Database connection pooling and query queueing.

/**
 * QueryQueue - sequential SQL query processing.
 *
 * @todo support transactions
 */

var EXTEND = require('util').inherits
  , Emitter = require("events").EventEmitter;

/**
 * Create SQL query queue.
 *
 * @param {Object} config
 */
function QueryQueue(config) {
  this.config = config;
  this.atomic = config.atomic;
  this.connection = config.connection;

  this.failure = config.failure || function (e) {throw e;};
  this.success = config.success || null;

  this.failed = false;
  this.paused = false;

  this.cptr = 0;
  this.steps = config.steps;
  this.lastStatement = null;
  this.nextArgs = null;

  QueryQueue.super_.call(this);
}

EXTEND(QueryQueue, Emitter);

QueryQueue.prototype.QUERY_FAIL = 0;
QueryQueue.prototype.QUERY_SUCCESS = 1;

/**
 */
QueryQueue.prototype.silentErrorHandler = function () {

};

/**
 * Execute failure callback for this queue step and exit.
 * @public
 */
QueryQueue.prototype.fail = function (error) {
  this.failed = true;

  (this.lastStatement.failure || this.failure).call(this, error);
  this.emit('complete', this.QUERY_FAIL, this);
};

/**
 * Execute next statement and loop until queue is processed or paused.
 */
QueryQueue.prototype.go = function () {
  var stat = this.lastStatement = this.steps[this.cptr++];


  this.paused = false;

  if (this.cptr <= this.steps.length) {
    var q = this;

    if (this.nextArgs) {
      stat.args = this.nextArgs;
      this.nextArgs = null;
    }

    this.connection.query(stat.query, stat.args, function (err, rows) {
      if (err) {
        q.fail(err);
      }
      // Empty SELECT is bad.
      else if (!rows[0] && stat.query.toUpperCase().indexOf('SELECT') === 0) {
        q.fail('Error: no result');
      }
      else {
        (stat.success || q.success).call(q, rows);
        (q.failed === false || q.paused === true) && q.go();
      }
    });
  }
  else {
    this.emit('complete', this.QUERY_SUCCESS, this);
  }
};


/**
 * Stop processing (.go method will start it again).
 *
 * @public
 */
QueryQueue.prototype.halt = function () {
  this.paused = true;
};

/**
 * Set arguments for next query.
 *
 * @public
 * @param ...
 *   Variable number of arguments passed to next query.
 */
QueryQueue.prototype.setNextArgs = function () {
  this.nextArgs = Array.prototype.slice.call(arguments, 0);
};


//
exports.QueryQueue = QueryQueue;