transaction.ts: simplify the logic by going back to using SnapshotVersion.min() to represent a deleted document rather than null

Author: dconeybe

packages/firestore/src/core/transaction.ts

@@ -34,26 +34,13 @@ import { Code, FirestoreError } from '../util/error';
 
 import { SnapshotVersion } from './snapshot_version';
 
-function nullableSnapshotVersionsEqual(
-  v1: SnapshotVersion | null,
-  v2: SnapshotVersion | null
-): boolean {
-  if (v1 === v2) {
-    return true;
-  } else if (v1 === null || v2 === null) {
-    return false;
-  } else {
-    return v1.isEqual(v2);
-  }
-}
-
 /**
  * Internal transaction object responsible for accumulating the mutations to
  * perform and the base versions for any documents read.
  */
 export class Transaction {
   // The version of each document that was read during this transaction.
-  private readVersions = new Map</* path */ string, SnapshotVersion | null>();
+  private readVersions = new Map</* path */ string, SnapshotVersion>();
   private mutations: Mutation[] = [];
   private committed = false;
 
@@ -128,20 +115,20 @@ export class Transaction {
   }
 
   private recordVersion(doc: Document): void {
-    let docVersion: SnapshotVersion | null;
+    let docVersion: SnapshotVersion;
 
     if (doc.isFoundDocument()) {
       docVersion = doc.version;
     } else if (doc.isNoDocument()) {
-      // For deleted docs, we must use {exists: false} when we overwrite them.
-      docVersion = null;
+      // Represent a deleted doc using SnapshotVersion.min().
+      docVersion = SnapshotVersion.min();
     } else {
       throw fail('Document in a transaction was a ' + doc.constructor.name);
     }
 
     const existingVersion = this.readVersions.get(doc.key.toString());
-    if (existingVersion !== undefined) {
-      if (!nullableSnapshotVersionsEqual(existingVersion, docVersion)) {
+    if (existingVersion) {
+      if (!docVersion.isEqual(existingVersion)) {
         // This transaction will fail no matter what.
         throw new FirestoreError(
           Code.ABORTED,
@@ -159,8 +146,8 @@ export class Transaction {
    */
   private precondition(key: DocumentKey): Precondition {
     const version = this.readVersions.get(key.toString());
-    if (!this.writtenDocs.has(key.toString()) && version !== undefined) {
-      if (version == null) {
+    if (!this.writtenDocs.has(key.toString()) && version) {
+      if (version.isEqual(SnapshotVersion.min())) {
         return Precondition.exists(false);
       } else {
         return Precondition.updateTime(version);
@@ -177,8 +164,8 @@ export class Transaction {
     const version = this.readVersions.get(key.toString());
     // The first time a document is written, we want to take into account the
     // read time and existence
-    if (!this.writtenDocs.has(key.toString()) && version !== undefined) {
-      if (version === null) {
+    if (!this.writtenDocs.has(key.toString()) && version) {
+      if (version.isEqual(SnapshotVersion.min())) {
         // The document doesn't exist, so fail the transaction.
 
         // This has to be validated locally because you can't send a