Update `FieldValue` For Porting `Mutation`s to C++ (#1144)

* update FieldValue for Mutation implementation

* address changes

* address changes

* address change

1 files changed, 6 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/model/document.h b/Firestore/core/src/firebase/firestore/model/document.h
index 50a7b90..1b7cc13 100644
--- a/Firestore/core/src/firebase/firestore/model/document.h
+++ b/Firestore/core/src/firebase/firestore/model/document.h
@@ -17,8 +17,10 @@
 #ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_H_
 #define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_H_
 
+#include "Firestore/core/src/firebase/firestore/model/field_path.h"
 #include "Firestore/core/src/firebase/firestore/model/field_value.h"
 #include "Firestore/core/src/firebase/firestore/model/maybe_document.h"
+#include "absl/types/optional.h"
 
 namespace firebase {
 namespace firestore {
@@ -42,6 +44,10 @@ class Document : public MaybeDocument {
     return data_;
   }
 
+  absl::optional<FieldValue> field(const FieldPath& path) const {
+    return data_.Get(path);
+  }
+
   bool has_local_mutations() const {
     return has_local_mutations_;
   }