Forcibly adding NeDB events by deriving from the Datastore prototype

EventedDatastore.js

// IMPORTANT:
// As of nedb@^1.7.0, Datastore now inherits from EventEmitter in the NeDB core module.
// If you need to support older versions of NeDB, please look at the following previous revision
// of this gist:
//    https://gist.github.com/JamesMGreene/0e0b2506c7bd2a2557f7/d8b4b1e97bb0d118c509672e3c7276b6dc4ba13a


/*
This gist provides a module which derives from the NeDB Datastore module and extends it to
emit several important events:
  - "load": an event that is emitted when a datastore is fully loaded (or errs and fails to load)
      - callback:  function( err ) { ... }
  - "inserted": an event that is emitted once for EACH new document that is inserted into a datastore
      - callback:  function( newDoc ) { ... }
  - "updated": an event that is emitted once for EACH existing document that is updated within a datastore
      - callback:  function( newDoc, oldDoc ) { ... }
  - "removed": an event that is emitted once for EACH existing document that is removed from a datastore
      - callback:  function( oldDoc ) { ... }

*/


var util = require('util');
var Datastore = require('nedb');


function EventedDatastore( options ) {
  if ( !(this instanceof EventedDatastore) ) {
    return new EventedDatastore( options );
  }

  var self = this;

  options = options || {};

  var autoLoadOption = options.autoload || false;
  options.autoload = false;

  Datastore.call( self, options );
  options.autoload = autoLoadOption;
  self.autoload = autoLoadOption;

  // Temporary properties used to collect data for event emissions
  self.__removedDocs = null;
  self.__modifications = null;

  if ( self.autoload ) {
    // Wait till the next tick to allow time for event listeners to be attached
    process.nextTick(function() {
      self.loadDatabase( options.onload );
    });
  }
}

util.inherits( EventedDatastore, Datastore );



EventedDatastore.prototype.loadDatabase = function( cb ) {
  var self = this;
  var callback = typeof cb === 'function' ? cb : function( err ) {
      if ( err ) {
        throw err;
      }
    };

  var eventedCallback = function( err ) {
    process.nextTick(function() {
      self.emit( 'load', err );
      callback( err );
    });
  };

  try {
    return Datastore.prototype.loadDatabase.call( self, eventedCallback );
  }
  catch ( err ) {
    eventedCallback.call( self, err );
  }
};


EventedDatastore.prototype._insert = function( newDoc, cb ) {
  var self = this;
  var callback = typeof cb === 'function' ? cb : function() {};

  var eventedCallback = function( err, newDocs ) {
    process.nextTick(function() {
      if ( err ) {
        return callback( err, newDocs );
      }

      var newDocsArr = util.isArray( newDocs ) ? newDocs : [ newDocs ];

      // Ensure there are listeners registered before making a bunch of unnecessary function calls to `emit`
      if ( self.listeners( 'inserted' ).length > 0 ) {
        newDocsArr.forEach(function( newDoc ) {
          self.emit( 'inserted', newDoc );
        });
      }

      callback( null, newDocs );
    });
  };

  try {
    return Datastore.prototype._insert.call( self, newDoc, eventedCallback );
  }
  catch ( err ) {
    eventedCallback.call( self, err );
  }
};


EventedDatastore.prototype.updateIndexes = function( modifications ) {
  // Add a new temporary property
  this.__modifications = modifications;

  return Datastore.prototype.updateIndexes.apply( this, arguments );
};


EventedDatastore.prototype._update = function( query, updateQuery, options, cb ) {
  var self = this;

  if ( typeof options === 'function' ) {
    cb = options;
    options = {};
  }
  if ( options == null ) {
    options = {};
  }
  var callback = typeof cb === 'function' ? cb : function() {};

  var eventedCallback = function( err, numAffected, newDocOrAffectedDocs ) {
    process.nextTick(function() {
      if ( err ) {
        return callback( err );
      }

      var modifications = self.__modifications || [];
      if ( modifications && modifications.length > 0 ) {
        // Remove the temporary property
        self.__modifications = null;

        // Ensure there are listeners registered before making a bunch of unnecessary function calls to `emit`
        if ( self.listeners( 'updated' ).length > 0 ) {
          modifications.forEach(function( mod ) {
            self.emit( 'updated', mod.newDoc, mod.oldDoc );
          });
        }
      }

      var isNewDoc =  modifications.length === 0 && numAffected === 1 && !!newDocOrAffectedDocs;
      var newDocsArr = util.isArray( newDocOrAffectedDocs ) ? newDocOrAffectedDocs : [ newDocOrAffectedDocs ];
      var affectedDocsArr = options.returnUpdatedDocs === true ? modifications.map(function( mod ) { return mod.newDoc; }) : undefined;

      var affectedDocs = isNewDoc ? newDocsArr : affectedDocsArr;
      callback( null, numAffected, affectedDocs );
    });
  };

  try {
    return Datastore.prototype._update.call( self, query, updateQuery, options, eventedCallback );
  }
  catch ( err ) {
    eventedCallback.call( self, err );
  }
};


EventedDatastore.prototype._remove = function( query, options, cb ) {
  var self = this;

  if ( typeof options === 'function' ) {
    cb = options;
    options = {};
  }
  var callback = typeof cb === 'function' ? cb : function() {};

  var eventedCallback = function( err, numRemoved ) {
    process.nextTick(function() {
      if ( err ) {
        return callback( err );
      }

      var removedDocs = self.__removedDocs || [];

      // Remove the temporary property
      self.__removedDocs = null;

      if ( removedDocs && removedDocs.length > 0 ) {
        // Ensure there are listeners registered before making a bunch of unnecessary function calls to `emit`
        if ( self.listeners( 'removed' ).length > 0 ) {
          removedDocs.forEach(function( oldDoc ) {
            self.emit( 'removed', oldDoc );
          });
        }
      }

      callback( null, numRemoved );
    });
  };

  try {
    return Datastore.prototype._remove.call( self, query, options, eventedCallback );
  }
  catch ( err ) {
    eventedCallback.call( self, err );
  }
};


EventedDatastore.prototype.removeFromIndexes = function( doc /*, cb */ ) {
  var self = this;

  // Add a new temporary property
  if ( !self.__removedDocs ) {
    self.__removedDocs = [];
  }
  self.__removedDocs.push( doc );

  return Datastore.prototype.removeFromIndexes.apply( self, arguments );
};



module.exports = EventedDatastore;