Projection function added to cursor

lib/cursor.js

@@ -1,7 +1,9 @@
 /**
  * Manage access to data, be it to find, update or remove it
  */
-var model = require('./model');
+var model = require('./model')
+  , _ = require('underscore')
+  ;
 
 
 
@@ -38,7 +40,7 @@ Cursor.prototype.skip = function(skip) {
 
 /**
  * Sort results of the query
- * @Param {SortQuery} sortQuery - SortQuery is { field: order }, field can use the dot-notation, order is 1 for ascending and -1 for descending
+ * @param {SortQuery} sortQuery - SortQuery is { field: order }, field can use the dot-notation, order is 1 for ascending and -1 for descending
  */
 Cursor.prototype.sort = function(sortQuery) {
   this._sort = sortQuery;
@@ -46,6 +48,50 @@ Cursor.prototype.sort = function(sortQuery) {
 };
 
 
+/**
+ * Add the use of a projection
+ * @param {Object} projection - MongoDB-style projection. {} means take all fields. Then it's {key1:1, key2:1} to take only key1 and key2
+ *                              {key1: 0, key2: 0} to omit only key1 and key2. Except _id, you can't mix takes and omits
+ */
+Cursor.prototype.projection = function(projection) {
+  this._projection = projection;
+  return this;
+};
+
+
+/**
+ * Apply the projection
+ */
+Cursor.prototype.project = function (candidates) {
+  var res = [], self = this
+    , keepId, action, keys
+    ;
+
+  if (this._projection === undefined || Object.keys(this._projection).length === 0) {
+    return candidates;
+  }
+
+  keepId = this._projection._id === 0 ? false : true;
+  this._projection = _.omit(this._projection, '_id');
+
+  // Check for consistency
+  keys = Object.keys(this._projection);
+  keys.forEach(function (k) {
+    if (action !== undefined && self._projection[k] !== action) { throw "Can't both keep and omit fields except for _id"; }
+    action = self._projection[k];
+  });
+
+  // Do the actual projection
+  candidates.forEach(function (candidate) {
+    var toPush = action === 1 ? _.pick(candidate, keys) : _.omit(candidate, keys);
+    if (keepId) { toPush._id = candidate._id; }
+    res.push(candidate);
+  });
+
+  return res;
+};
+
+
 /**
  * Get all matching elements
  * Will return pointers to matched elements (shallow copies), returning full copies is the role of find or findOne
@@ -56,6 +102,7 @@ Cursor.prototype.sort = function(sortQuery) {
 Cursor.prototype._exec = function(callback) {
   var candidates = this.db.getCandidates(this.query)
     , res = [], added = 0, skipped = 0, self = this
+    , error = null
     , i, keys, key
     ;
 
@@ -109,10 +156,18 @@ Cursor.prototype._exec = function(callback) {
     res = res.slice(skip, skip + limit);
   }
 
+  // Apply projection
+  try {
+    res = this.project(res);
+  } catch (e) {
+    error = e;
+    res = null;
+  }
+
   if (this.execFn) {
-    return this.execFn(null, res, callback);
+    return this.execFn(error, res, callback);
   } else {
-    return callback(null, res);
+    return callback(error, res);
   }
 };
 

lib/datastore.js

@@ -376,6 +376,7 @@ Datastore.prototype.count = function(query, callback) {
  * Find all documents matching the query
  * If no callback is passed, we return the cursor so that user can limit, skip and finally exec
  * @param {Object} query MongoDB-style query
+ * @param {Object} projection MongoDB-style projection
  */
 Datastore.prototype.find = function (query, projection, callback) {
   switch (arguments.length) {
@@ -387,7 +388,7 @@ Datastore.prototype.find = function (query, projection, callback) {
       if (typeof projection === 'function') {
         callback = projection;
         projection = {};
-      }
+      }   // If not assume projection is an object and callback undefined
       break;
   }