Make MaybeDocument an abstract class

packages/firestore/src/api/database.ts

@@ -594,8 +594,11 @@ export class Transaction implements firestore.Transaction {
         const doc = docs[0];
         if (doc instanceof NoDocument) {
           return new DocumentSnapshot(this._firestore, ref._key, null, false);
+        } else if (doc instanceof Document) {
+          return new DocumentSnapshot(this._firestore, ref._key, doc, false);
+        } else {
+          fail('MaybeDocument is neither Document nor NoDocument');
         }
-        return new DocumentSnapshot(this._firestore, ref._key, doc, false);
       });
   }
 

packages/firestore/src/model/document.ts

@@ -26,15 +26,32 @@ export interface DocumentOptions {
   hasLocalMutations: boolean;
 }
 
-export class Document {
+/**
+ * The result of a lookup for a given path may be an existing document or a
+ * marker that this document does not exist at a given version.
+ */
+export abstract class MaybeDocument {
+  constructor(readonly key: DocumentKey, readonly version: SnapshotVersion) {}
+
+  static compareByKey(d1: MaybeDocument, d2: MaybeDocument): number {
+    return DocumentKey.comparator(d1.key, d2.key);
+  }
+}
+
+/**
+ * Represents a document in Firestore with a key, version, data and whether the
+ * data has local mutations applied to it.
+ */
+export class Document extends MaybeDocument {
   readonly hasLocalMutations: boolean;
 
   constructor(
-    readonly key: DocumentKey,
-    readonly version: SnapshotVersion,
+    key: DocumentKey,
+    version: SnapshotVersion,
     readonly data: ObjectValue,
     options: DocumentOptions
   ) {
+    super(key, version);
     this.hasLocalMutations = options.hasLocalMutations;
   }
 
@@ -68,10 +85,6 @@ export class Document {
     );
   }
 
-  static compareByKey(d1: MaybeDocument, d2: MaybeDocument): number {
-    return DocumentKey.comparator(d1.key, d2.key);
-  }
-
   static compareByField(field: FieldPath, d1: Document, d2: Document): number {
     const v1 = d1.field(field);
     const v2 = d2.field(field);
@@ -88,8 +101,10 @@ export class Document {
  * Version is set to 0 if we don't point to any specific time, otherwise it
  * denotes time we know it didn't exist at.
  */
-export class NoDocument {
-  constructor(readonly key: DocumentKey, readonly version: SnapshotVersion) {}
+export class NoDocument extends MaybeDocument {
+  constructor(key: DocumentKey, version: SnapshotVersion) {
+    super(key, version);
+  }
 
   toString(): string {
     return `NoDocument(${this.key}, ${this.version})`;
@@ -102,14 +117,4 @@ export class NoDocument {
       other.key.isEqual(this.key)
     );
   }
-
-  static compareByKey(d1: MaybeDocument, d2: MaybeDocument): number {
-    return DocumentKey.comparator(d1.key, d2.key);
-  }
 }
-
-/**
- * A union type representing either a full document or a deleted document.
- * The NoDocument is used when it doesn't exist on the server.
- */
-export type MaybeDocument = Document | NoDocument;

packages/firestore/src/remote/watch_change.ts

@@ -61,7 +61,7 @@ export class DocumentWatchChange {
      * The new document or NoDocument if it was deleted. Is null if the
      * document went out of view without the server sending a new document.
      */
-    public newDoc: Document | NoDocument | null
+    public newDoc: MaybeDocument | null
   ) {}
 }
 

packages/firestore/test/util/helpers.ts

@@ -317,10 +317,7 @@ export function updateMapping(
     modifiedDocuments = modifiedDocuments.add(k);
   });
   removed.forEach(docOrKey => {
-    const k =
-      docOrKey instanceof Document || docOrKey instanceof NoDocument
-        ? docOrKey.key
-        : key(docOrKey);
+    const k = docOrKey instanceof MaybeDocument ? docOrKey.key : key(docOrKey);
     removedDocuments = removedDocuments.add(k);
   });