[cloud_firestore] Add FieldPath

[creativecreatorormaybenot]

Description

This brought my attention to FieldPath again. While my solution on StackOverflow works, it is not particularly nice to use.

Related Issues

• FieldPath #617

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• If the pull request affects only one plugin, the PR title starts with the name of the plugin in brackets (e.g. [cloud_firestore])
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See [Contributor Guide]).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the [Flutter Style Guide].
• I updated pubspec.yaml with an appropriate new version according to the [pub versioning philosophy].
• I updated CHANGELOG.md to add a description of the change.
• I signed the [CLA].
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• No, this is not a breaking change.

[collinjackson]

Thanks for adding tests! It seems like we're relying on an implementation detail (the sentinel value is "__name__") and instead I think we should implement it in the same way as FieldValue and call the native version of FieldPath.documentId.

https://github.com/FirebaseExtended/flutterfire/blob/a24db9c4dac979989b86838069095b95ab2202a9/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java#L917

[creativecreatorormaybenot]

@collinjackson What kind of formatter are you using in flutterfire?

When I use the formatter (which the IDE does automatically 😞), the whole file is changed and the Cirrus CI test also fails.. It is very cumbersome for me to manually adjust the format.

[collinjackson]

@collinjackson What kind of formatter are you using in flutterfire?

When I use the formatter (which the IDE does automatically 😞), the whole file is changed and the Cirrus CI test also fails.. It is very cumbersome for me to manually adjust the format.

We're using pub global run flutter_plugin_tools format. That's all I know...

Pro tip: The failure message gives you a patch command that will fix the formatting for you:

patch -p1 <<DONE
diff --git a/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java b/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java
index f231617..524589d 100644
--- a/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java
+++ b/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java
@@ -133,14 +133,15 @@ public class CloudFirestorePlugin implements MethodCallHandler {
         if (field instanceof FieldPath) {
           if (field == FieldPath.documentId()) {
-            throw new IllegalArgumentException("You cannot use {start/end}{At/After}Document " +
-                    "when ordering by the document id. When using any of the mentioned methods, " +
-                    "the library will order by the document id implicitly as " +
-                    "it needs to add other fields to the order clause.");
+            throw new IllegalArgumentException(
+                "You cannot use {start/end}{At/After}Document "
+                    + "when ordering by the document id. When using any of the mentioned methods, "
+                    + "the library will order by the document id implicitly as "
+                    + "it needs to add other fields to the order clause.");
           } else {
             // Unsupported type.
           }
-        } else if (field instanceof  String) {
+        } else if (field instanceof String) {
           String orderByFieldName = (String) field;
           if (orderByFieldName.contains(".")) {
             String[] fieldNameParts = orderByFieldName.split("\\.");
@@ -313,7 +314,7 @@ public class CloudFirestorePlugin implements MethodCallHandler {
       boolean descending = (boolean) order.get(1);
       Query.Direction direction =
-              descending ? Query.Direction.DESCENDING : Query.Direction.ASCENDING;
+          descending ? Query.Direction.DESCENDING : Query.Direction.ASCENDING;
       if (fieldName != null) {
         query = query.orderBy(fieldName, direction);
diff --git a/packages/cloud_firestore/lib/src/field_path.dart b/packages/cloud_firestore/lib/src/field_path.dart
index e144cd0..64cdde8 100644
--- a/packages/cloud_firestore/lib/src/field_path.dart
+++ b/packages/cloud_firestore/lib/src/field_path.dart
@@ -16,5 +16,6 @@ class FieldPath {
   final _FieldPathType type;
   /// The path to the document id, which can be used in queries.
-  static FieldPath get documentId => const FieldPath._(_FieldPathType.documentId);
+  static FieldPath get documentId =>
+      const FieldPath._(_FieldPathType.documentId);
 }
diff --git a/packages/cloud_firestore/lib/src/firestore_message_codec.dart b/packages/cloud_firestore/lib/src/firestore_message_codec.dart
index 1a555fc..9f658cd 100644
--- a/packages/cloud_firestore/lib/src/firestore_message_codec.dart
+++ b/packages/cloud_firestore/lib/src/firestore_message_codec.dart
@@ -34,7 +34,7 @@ class FirestoreMessageCodec extends StandardMessageCodec {
   static const Map<_FieldPathType, int> _kFieldPathCodes =
       <_FieldPathType, int>{
     _FieldPathType.documentId: _kDocumentId,
-      };
+  };
   @override
   void writeValue(WriteBuffer buffer, dynamic value) {
diff --git a/packages/cloud_firestore/test/cloud_firestore_test.dart b/packages/cloud_firestore/test/cloud_firestore_test.dart
index d437202..63a3f06 100755
--- a/packages/cloud_firestore/test/cloud_firestore_test.dart
+++ b/packages/cloud_firestore/test/cloud_firestore_test.dart
@@ -1264,7 +1264,8 @@ bool _deepEquals(dynamic valueA, dynamic valueB) {
   if (valueA is FieldValue) {
     return valueB is FieldValue && _deepEqualsFieldValue(valueA, valueB);
   }
-  if (valueA is FieldPath) return valueB is FieldPath && valueA.type == valueB.type;
+  if (valueA is FieldPath)
+    return valueB is FieldPath && valueA.type == valueB.type;
   return valueA == valueB;
 }
DONE

[creativecreatorormaybenot]

@collinjackson Thanks a bunch!

[creativecreatorormaybenot]

I think that I am done with the new implementation. I added some exceptions that will help users understand what about their queries was incorrect and most importantly added assertions when possible.

[creativecreatorormaybenot]

@collinjackson Can you review again?

[collinjackson]

thanks, this lgtm