# All files / core transaction.ts

96.83% Statements 61/63
86.36% Branches 19/22
100% Functions 15/15
96.61% Lines 57/59

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     /**
     * Copyright 2017 Google Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    import { ParsedSetData, ParsedUpdateData } from '../api/user_data_converter';
    import { SnapshotVersion } from './snapshot_version';
    import { documentVersionMap } from '../model/collections';
    import { NoDocument } from '../model/document';
    import { MaybeDocument } from '../model/document';
    import { DocumentKey } from '../model/document_key';
    import { DeleteMutation, Mutation, Precondition } from '../model/mutation';
    import { Datastore } from '../remote/datastore';
    import { Code, FirestoreError } from '../util/error';

    /**
     * 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 = documentVersionMap();
      private mutations: Mutation[] = [];
      private committed = false;

      constructor(private datastore: Datastore) {}

      private recordVersion(doc: MaybeDocument) {
        let docVersion = doc.version;
        if (doc instanceof NoDocument) {
          // For deleted docs, we must use baseVersion 0 when we overwrite them.
          docVersion = SnapshotVersion.forDeletedDoc();
        }
        const existingVersion = this.readVersions.get(doc.key);
        if (existingVersion !== null) {
          Eif (!docVersion.isEqual(existingVersion)) {
            // This transaction will fail no matter what.
            throw new FirestoreError(
              Code.ABORTED,
              'Document version changed between two reads.'
            );
          }
        } else {
          this.readVersions = this.readVersions.insert(doc.key, docVersion);
        }
      }

      lookup(keys: DocumentKey[]): Promise<MaybeDocument[]> {
        Iif (this.committed) {
          return Promise.reject<MaybeDocument[]>(
            'Transaction has already completed.'
          );
        }
        if (this.mutations.length > 0) {
          return Promise.reject<MaybeDocument[]>(
            'Transactions lookups are invalid after writes.'
          );
        }
        return this.datastore.lookup(keys).then(docs => {
          docs.forEach(doc => this.recordVersion(doc));
          return docs;
        });
      }

      private write(mutations: Mutation[]) {
        Iif (this.committed) {
          throw new FirestoreError(
            Code.FAILED_PRECONDITION,
            'Transaction has already completed.'
          );
        }
        this.mutations = this.mutations.concat(mutations);
      }

      /**
       * Returns the version of this document when it was read in this transaction,
       * as a precondition, or no precondition if it was not read.
       */
      private precondition(key: DocumentKey): Precondition {
        const version = this.readVersions.get(key);
        if (version) {
          return Precondition.updateTime(version);
        } else {
          return Precondition.NONE;
        }
      }

      /**
       * Returns the precondition for a document if the operation is an update.
       */
      private preconditionForUpdate(key: DocumentKey): Precondition {
        const version = this.readVersions.get(key);
        if (version && version.isEqual(SnapshotVersion.forDeletedDoc())) {
          // The document doesn't exist, so fail the transaction.
          throw new FirestoreError(
            Code.FAILED_PRECONDITION,
            "Can't update a document that doesn't exist."
          );
        } else if (version) {
          // Document exists, base precondition on document update time.
          return Precondition.updateTime(version);
        } else {
          // Document was not read, so we just use the preconditions for a blind
          // update.
          return Precondition.exists(true);
        }
      }

      set(key: DocumentKey, data: ParsedSetData) {
        this.write(data.toMutations(key, this.precondition(key)));
      }

      update(key: DocumentKey, data: ParsedUpdateData) {
        this.write(data.toMutations(key, this.preconditionForUpdate(key)));
      }

      delete(key: DocumentKey) {
        this.write([new DeleteMutation(key, this.precondition(key))]);
        // Since the delete will be applied before all following writes, we need to
        // ensure that the precondition for the next write will be exists: false.
        this.readVersions = this.readVersions.insert(
          key,
          SnapshotVersion.forDeletedDoc()
        );
      }

      commit(): Promise<void> {
        let unwritten = this.readVersions;
        // For each mutation, note that the doc was written.
        this.mutations.forEach(mutation => {
          unwritten = unwritten.remove(mutation.key);
        });
        if (!unwritten.isEmpty()) {
          return Promise.reject(
            Error('Every document read in a transaction must also be written.')
          );
        }
        return this.datastore.commit(this.mutations).then(() => {
          this.committed = true;
        });
      }
    }