feat: select only specified fields for return

lib/index.js

@@ -134,6 +134,32 @@ DataStore.prototype.prepareQuery = function (query, options) {
   return query
 }
 
+/**
+ * Determines the list of properties to select from each document before returning. If an array is specified
+ * it is returned. If an object is specified an array is created containing all the keys that have a value equal to 1.
+ * The `_id` property is added if not already specified.
+ *
+ * @param {Array|Object} fields - an array of field names or an object such as `{"title": 1}`
+ * @returns {Array} an array of property names to be selected from each document
+ */
+DataStore.prototype.getFields = function (fields) {
+  if (_.isEmpty(fields)) {
+    return null
+  }
+
+  var preparedFields
+
+  if (!Array.isArray(fields)) {
+    preparedFields = Object.keys(fields).filter((field) => { return fields[field] === 1 })
+  } else {
+    preparedFields = fields
+  }
+
+  if (!preparedFields['_id']) preparedFields.push('_id')
+
+  return preparedFields
+}
+
 /**
  * Query the database
  *
@@ -145,6 +171,8 @@ DataStore.prototype.prepareQuery = function (query, options) {
  */
 DataStore.prototype.find = function (query, collection, options) {
   options = options || {}
+  var fields = this.getFields(options.fields)
+
   query = this.prepareQuery(query, options)
 
   debug('find in %s %o %o', collection, query, options)
@@ -156,6 +184,12 @@ DataStore.prototype.find = function (query, collection, options) {
 
         var results = res.docs
 
+        if (fields) {
+          results = _.chain(results)
+          .map((result) => { return _.pick(result, fields) })
+          .value()
+        }
+
         return resolve(results)
       })
     }).catch((err) => {

test/unit/couchdb.js

@@ -136,7 +136,7 @@ describe('CouchDB', function () {
       })
     })
 
-    it.skip('should return only the fields specified by the `fields` property', function (done) {
+    it('should return only the fields specified by the `fields` property', function (done) {
       var couchdb = new CouchDBAdapter()
       couchdb.connect({ collection: 'users' }).then(() => {
         var users = [{ name: 'Ernie', age: 7, colour: 'yellow' }, { name: 'Oscar', age: 9, colour: 'green' }, { name: 'BigBird', age: 13, colour: 'yellow' }]