feat(document): add isDirectSelected() to minimize isSelected() changes

Fix #5063

lib/document.js

@@ -1237,6 +1237,65 @@ Document.prototype.isSelected = function isSelected(path) {
   return true;
 };
 
+/**
+ * Checks if `path` was explicitly selected. If no projection, always returns
+ * true.
+ *
+ * ####Example
+ *
+ *     Thing.findOne().select('nested.name').exec(function (err, doc) {
+ *        doc.isDirectSelected('nested.name') // true
+ *        doc.isDirectSelected('nested.otherName') // false
+ *        doc.isDirectSelected('nested')  // false
+ *     })
+ *
+ * @param {String} path
+ * @return {Boolean}
+ * @api public
+ */
+
+Document.prototype.isDirectSelected = function isDirectSelected(path) {
+  if (this.$__.selected) {
+    if (path === '_id') {
+      return this.$__.selected._id !== 0;
+    }
+
+    var paths = Object.keys(this.$__.selected);
+    var i = paths.length;
+    var inclusive = null;
+    var cur;
+
+    if (i === 1 && paths[0] === '_id') {
+      // only _id was selected.
+      return this.$__.selected._id === 0;
+    }
+
+    while (i--) {
+      cur = paths[i];
+      if (cur === '_id') {
+        continue;
+      }
+      if (this.$__.selected[cur] && this.$__.selected[cur].$meta) {
+        continue;
+      }
+      inclusive = !!this.$__.selected[cur];
+      break;
+    }
+
+    if (inclusive === null) {
+      return true;
+    }
+
+    if (path in this.$__.selected) {
+      return inclusive;
+    }
+
+    return !inclusive;
+  }
+
+  return true;
+};
+
 /**
  * Executes registered validation rules for this document.
  *