Add Query.MatchesAllDocuments() (#3990)

Author: schmidt-sebastian

Firestore/core/src/firebase/firestore/core/query.cc

@@ -57,6 +57,13 @@ bool Query::IsDocumentQuery() const {
          filters_.empty();
 }
 
+bool Query::MatchesAllDocuments() const {
+  return filters_.empty() && limit_ == kNoLimit && !start_at_ && !end_at_ &&
+         (explicit_order_bys_.empty() ||
+          (explicit_order_bys_.size() == 1 &&
+           explicit_order_bys_.front().field().IsKeyFieldPath()));
+}
+
 const FieldPath* Query::InequalityFilterField() const {
   for (const auto& filter : filters_) {
     if (filter.IsInequality()) {

Firestore/core/src/firebase/firestore/core/query.h

@@ -99,6 +99,12 @@ class Query {
     return collection_group_ != nullptr;
   }
 
+  /**
+   * Returns true if this query does not specify any query constraints that
+   * could remove results.
+   */
+  bool MatchesAllDocuments() const;
+
   /** The filters on the documents returned by the query. */
   const FilterList& filters() const {
     return filters_;

Firestore/core/test/firebase/firestore/core/query_test.cc

@@ -708,6 +708,29 @@ TEST(QueryTest, CanonicalIDs) {
                                      "desc|lb:b:OAK1000|ub:a:SFO2000"));
 }
 
+TEST(QueryTest, MatchesAllDocuments) {
+  auto baseQuery = testutil::Query("coll");
+  EXPECT_TRUE(baseQuery.MatchesAllDocuments());
+
+  auto query = baseQuery.AddingOrderBy(OrderBy("__name__"));
+  EXPECT_TRUE(query.MatchesAllDocuments());
+
+  query = baseQuery.AddingOrderBy(OrderBy("foo"));
+  EXPECT_FALSE(query.MatchesAllDocuments());
+
+  query = baseQuery.AddingFilter(Filter("foo", "==", "bar"));
+  EXPECT_FALSE(query.MatchesAllDocuments());
+
+  query = baseQuery.WithLimit(1);
+  EXPECT_FALSE(query.MatchesAllDocuments());
+
+  query = baseQuery.StartingAt(Bound({Value("SFO")}, true));
+  EXPECT_FALSE(query.MatchesAllDocuments());
+
+  query = baseQuery.StartingAt(Bound({Value("OAK")}, true));
+  EXPECT_FALSE(query.MatchesAllDocuments());
+}
+
 }  // namespace core
 }  // namespace firestore
 }  // namespace firebase