Port TargetIndexMatcher (#5975)

Author: schmidt-sebastian

packages/firestore/src/model/target_index_matcher.ts

@@ -0,0 +1,212 @@
+/**
+ * @license
+ * Copyright 2022 Google LLC
+ *
+ * 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 {
+  Direction,
+  FieldFilter,
+  Operator,
+  OrderBy,
+  Target
+} from '../core/target';
+import { debugAssert } from '../util/assert';
+
+import {
+  FieldIndex,
+  fieldIndexGetArraySegment,
+  fieldIndexGetDirectionalSegments,
+  IndexKind,
+  IndexSegment
+} from './field_index';
+
+/**
+ * A light query planner for Firestore.
+ *
+ * This class matches a `FieldIndex` against a Firestore Query `Target`. It
+ * determines whether a given index can be used to serve the specified target.
+ *
+ * The following table showcases some possible index configurations:
+ *
+ * Query                                               | Index
+ * -----------------------------------------------------------------------------
+ * where('a', '==', 'a').where('b', '==', 'b')         | a ASC, b DESC
+ * where('a', '==', 'a').where('b', '==', 'b')         | a ASC
+ * where('a', '==', 'a').where('b', '==', 'b')         | b DESC
+ * where('a', '>=', 'a').orderBy('a')                  | a ASC
+ * where('a', '>=', 'a').orderBy('a', 'desc')          | a DESC
+ * where('a', '>=', 'a').orderBy('a').orderBy('b')     | a ASC, b ASC
+ * where('a', '>=', 'a').orderBy('a').orderBy('b')     | a ASC
+ * where('a', 'array-contains', 'a').orderBy('b')      | a CONTAINS, b ASCENDING
+ * where('a', 'array-contains', 'a').orderBy('b')      | a CONTAINS
+ */
+export class TargetIndexMatcher {
+  // The collection ID (or collection group) of the query target.
+  private readonly collectionId: string;
+  // The single inequality filter of the target (if it exists).
+  private readonly inequalityFilter?: FieldFilter;
+  // The list of equality filters of the target.
+  private readonly equalityFilters: FieldFilter[];
+  // The list of orderBys of the target.
+  private readonly orderBys: OrderBy[];
+
+  constructor(target: Target) {
+    this.collectionId =
+      target.collectionGroup != null
+        ? target.collectionGroup
+        : target.path.lastSegment();
+    this.orderBys = target.orderBy;
+    this.equalityFilters = [];
+
+    for (const filter of target.filters) {
+      const fieldFilter = filter as FieldFilter;
+      if (fieldFilter.isInequality()) {
+        debugAssert(
+          !this.inequalityFilter ||
+            this.inequalityFilter.field.isEqual(fieldFilter.field),
+          'Only a single inequality is supported'
+        );
+        this.inequalityFilter = fieldFilter;
+      } else {
+        this.equalityFilters.push(fieldFilter);
+      }
+    }
+  }
+
+  /**
+   * Returns whether the index can be used to serve the TargetIndexMatcher's
+   * target.
+   *
+   * An index is considered capable of serving the target when:
+   * - The target uses all index segments for its filters and orderBy clauses.
+   *   The target can have additional filter and orderBy clauses, but not
+   *   fewer.
+   * - If an ArrayContains/ArrayContainsAnyfilter is used, the index must also
+   *   have a corresponding `CONTAINS` segment.
+   * - All directional index segments can be mapped to the target as a series of
+   *   equality filters, a single inequality filter and a series of orderBy
+   *   clauses.
+   * - The segments that represent the equality filters may appear out of order.
+   * - The optional segment for the inequality filter must appear after all
+   *   equality segments.
+   * - The segments that represent that orderBy clause of the target must appear
+   *   in order after all equality and inequality segments. Single orderBy
+   *   clauses cannot be skipped, but a continuous orderBy suffix may be
+   *   omitted.
+   */
+  servedByIndex(index: FieldIndex): boolean {
+    debugAssert(
+      index.collectionGroup === this.collectionId,
+      'Collection IDs do not match'
+    );
+
+    // If there is an array element, find a matching filter.
+    const arraySegment = fieldIndexGetArraySegment(index);
+    if (
+      arraySegment !== undefined &&
+      !this.hasMatchingEqualityFilter(arraySegment)
+    ) {
+      return false;
+    }
+
+    const segments = fieldIndexGetDirectionalSegments(index);
+    let segmentIndex = 0;
+    let orderBysIndex = 0;
+
+    // Process all equalities first. Equalities can appear out of order.
+    for (; segmentIndex < segments.length; ++segmentIndex) {
+      // We attempt to greedily match all segments to equality filters. If a
+      // filter matches an index segment, we can mark the segment as used.
+      // Since it is not possible to use the same field path in both an equality
+      // and inequality/oderBy clause, we do not have to consider the possibility
+      // that a matching equality segment should instead be used to map to an
+      // inequality filter or orderBy clause.
+      if (!this.hasMatchingEqualityFilter(segments[segmentIndex])) {
+        // If we cannot find a matching filter, we need to verify whether the
+        // remaining segments map to the target's inequality and its orderBy
+        // clauses.
+        break;
+      }
+    }
+
+    // If we already have processed all segments, all segments are used to serve
+    // the equality filters and we do not need to map any segments to the
+    // target's inequality and orderBy clauses.
+    if (segmentIndex === segments.length) {
+      return true;
+    }
+
+    // If there is an inequality filter, the next segment must match both the
+    // filter and the first orderBy clause.
+    if (this.inequalityFilter !== undefined) {
+      const segment = segments[segmentIndex];
+      if (
+        !this.matchesFilter(this.inequalityFilter, segment) ||
+        !this.matchesOrderBy(this.orderBys[orderBysIndex++], segment)
+      ) {
+        return false;
+      }
+      ++segmentIndex;
+    }
+
+    // All remaining segments need to represent the prefix of the target's
+    // orderBy.
+    for (; segmentIndex < segments.length; ++segmentIndex) {
+      const segment = segments[segmentIndex];
+      if (
+        orderBysIndex >= this.orderBys.length ||
+        !this.matchesOrderBy(this.orderBys[orderBysIndex++], segment)
+      ) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  private hasMatchingEqualityFilter(segment: IndexSegment): boolean {
+    for (const filter of this.equalityFilters) {
+      if (this.matchesFilter(filter, segment)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  private matchesFilter(
+    filter: FieldFilter | undefined,
+    segment: IndexSegment
+  ): boolean {
+    if (filter === undefined || !filter.field.isEqual(segment.fieldPath)) {
+      return false;
+    }
+    const isArrayOperator =
+      filter.op === Operator.ARRAY_CONTAINS ||
+      filter.op === Operator.ARRAY_CONTAINS_ANY;
+    return (segment.kind === IndexKind.CONTAINS) === isArrayOperator;
+  }
+
+  private matchesOrderBy(orderBy: OrderBy, segment: IndexSegment): boolean {
+    if (!orderBy.field.isEqual(segment.fieldPath)) {
+      return false;
+    }
+    return (
+      (segment.kind === IndexKind.ASCENDING &&
+        orderBy.dir === Direction.ASCENDING) ||
+      (segment.kind === IndexKind.DESCENDING &&
+        orderBy.dir === Direction.DESCENDING)
+    );
+  }
+}