[firestore] add support for `DocumentSnapshot.get('dot.notated.field.path')`

lib/modules/database/DataSnapshot.js

@@ -51,7 +51,8 @@ export default class DataSnapshot {
    * @returns {Snapshot}
    */
   child(path: string): DataSnapshot {
-    const value = deepGet(this._value, path);
+    let value = deepGet(this._value, path);
+    if (value === undefined) value = null;
     const childRef = this.ref.child(path);
     return new DataSnapshot(childRef, {
       value,

lib/modules/firestore/DocumentSnapshot.js

@@ -5,7 +5,7 @@
 import DocumentReference from './DocumentReference';
 import FieldPath from './FieldPath';
 import Path from './Path';
-import { isObject } from '../../utils';
+import { isObject, deepGet } from '../../utils';
 import { parseNativeMap } from './utils/serialize';
 
 import type Firestore from './';
@@ -63,6 +63,6 @@ export default class DocumentSnapshot {
     if (fieldPath instanceof FieldPath) {
       return extractFieldPathData(this._data, fieldPath._segments);
     }
-    return this._data ? this._data[fieldPath] : undefined;
+    return this._data ? deepGet(this._data, fieldPath, '.') : undefined;
   }
 }

lib/utils/index.js

@@ -33,7 +33,7 @@ export function deepGet(
 
   while (i < len) {
     const key = keys[i++];
-    if (!tmp || !hasOwnProperty.call(tmp, key)) return null;
+    if (!tmp || !hasOwnProperty.call(tmp, key)) return undefined;
     tmp = tmp[key];
   }