copyCollection.js

/**
 * Copy one collection to another
 *
 * call as `mongo db template.js thisfile.js`
 *
 * See http://www.mongodb.org/display/DOCS/Developer+FAQ#DeveloperFAQ-HowdoIcopyallobjectsfromonedatabasecollectiontoanother
 * Allegedly, this is the only way to do it in mongodb. Implemented as a batch script
 *
 * This is a somewhat accademic script - don't use it. if you need to copy one collection to another the fastest way
 * is to do:
 *      mongoexport -d db -c sourcecollection | mongoimport -d db -c targetcollection --drop
 *
 * By faster here are some numbers from copying a random collection with a million rows (2GB of data):
 *     running this batch, step size 100, individual inserts, duration: 1147s
 *     running this batch, step size 100, batch inserts, duration: 1149s
 *     running a one line db.source.find().forEach(function(x) { db.target.insert(x); }): 1080s
 *     using mongo export piped to mongoimport: 300s
 *
 * However, it demonstrates how to write a script which optionally  buffers db activity and "commits" once per slice
 * instead of one row at a time.
 *
 * Define the (source) collection to copy, the (target) to collection - and run
 * Can either be run a row at a time - or using batchInserts
 *
 */

var options = {
  to: 'target',
  collection: 'items',
  fields: {},
  batchInserts: false
};

CopyCollection = new Batch(options, false);
CopyCollection.name = 'CopyCollection';

/**
 * process
 *
 * if we're in batchInsert mode - buffer the found row to the stack property
 * else, attempt to insert into the target collection
 *
 * @return void.
 */
CopyCollection.process = function() {
  this.out('processing ' + this.currentRow._id, 4);

  if (this.options.batchInserts) {
    this.stack.push(this.currentRow);
  } else {
    try {
      db[this.options.to].insert(this.currentRow);
    } catch (err) {
      out(err.message, 1);
    }
  }
};


/**
 * start
 *
 * Run the standard start function, then drop the destination collection
 *
 * @return bool.
 */
CopyCollection.originalStart = CopyCollection.start;
CopyCollection.start = function() {
  if (!this.originalStart()) {
    return false;
  }

  if (this.total) {
	  this.out('Dropping ' + this.options.to + ' collection', 1);
	  try {
		db[this.options.to].drop();
	  } catch (err) {
		out(err.message, 1);
	  }

	  this.stack = [];
  }

  return true;
};


/**
 * afterCursor
 *
 * IF we're in batchInsert mode - insert the buffered rows
 * Then call the original afterCursor method
 *
 * @param count $count.
 * @return bool.
 */
CopyCollection.originalAfterCursor = CopyCollection.afterCursor;
CopyCollection.afterCursor = function afterCursor(count) {
  if (this.options.batchInserts) {
    this.out('Bulk inserting ' + this.stack.length + ' rows into ' + this.options.to, 4);
    try {
      db[this.options.to].insert(this.stack);
    } catch (err) {
      out(err.message, 1);
    }
    this.stack = [];
  }

  return this.originalAfterCursor(count);
};

CopyCollection.run();