Nh/is empty (#1820)

* adding isEmpty method to Result and List

CHANGELOG.md

@@ -6,6 +6,7 @@ x.x.x Release notes (xxxx-xx-xx)
 * None.
 
 ### Enhancements
+* Added `isEmpty()` method on `Realm.Results` and `Realm.List`.
 * Added schema change listener to `Realm.addListener()` (#1825).
 
 ### Bug fixes

docs/collection.js

@@ -63,6 +63,13 @@ class Collection {
      */
     isValid() {}
 
+    /**
+     * Checks if this collection is empty.
+     * @returns {boolean} indicating if the collection is empty or not.
+     * @since 2.7.0
+     */
+    isEmpty() {}
+
     /**
      * Returns new _Results_ that represent this collection being filtered by the provided query.
      *

lib/index.d.ts

@@ -150,6 +150,11 @@ declare namespace Realm {
          */
         isValid(): boolean;
 
+        /**
+         * @returns boolean
+         */
+        isEmpty(): boolean;
+
         min(property?: string): number | Date | null;
         max(property?: string): number | Date | null;
         sum(property?: string): number | null;

src/js_list.hpp

@@ -74,6 +74,7 @@ struct ListClass : ClassDefinition<T, realm::js::List<T>, CollectionClass<T>> {
     static void filtered(ContextType, ObjectType, Arguments, ReturnValue &);
     static void sorted(ContextType, ObjectType, Arguments, ReturnValue &);
     static void is_valid(ContextType, ObjectType, Arguments, ReturnValue &);
+    static void is_empty(ContextType, ObjectType, Arguments, ReturnValue &);
     static void index_of(ContextType, ObjectType, Arguments, ReturnValue &);
 
     // observable
@@ -93,6 +94,7 @@ struct ListClass : ClassDefinition<T, realm::js::List<T>, CollectionClass<T>> {
         {"filtered", wrap<filtered>},
         {"sorted", wrap<sorted>},
         {"isValid", wrap<is_valid>},
+        {"isEmpty", wrap<is_empty>},
         {"indexOf", wrap<index_of>},
         {"min", wrap<compute_aggregate_on_collection<ListClass<T>, AggregateFunc::Min>>},
         {"max", wrap<compute_aggregate_on_collection<ListClass<T>, AggregateFunc::Max>>},
@@ -272,6 +274,11 @@ void ListClass<T>::is_valid(ContextType ctx, ObjectType this_object, Arguments a
     return_value.set(get_internal<T, ListClass<T>>(this_object)->is_valid());
 }
 
+template<typename T>
+void ListClass<T>::is_empty(ContextType ctx, ObjectType this_object, Arguments args, ReturnValue &return_value) {
+    return_value.set(get_internal<T, ListClass<T>>(this_object)->size() == 0);
+}
+
 template<typename T>
 void ListClass<T>::index_of(ContextType ctx, ObjectType this_object, Arguments args, ReturnValue &return_value) {
     auto fn = [&](auto&& row) {

src/js_results.hpp

@@ -87,6 +87,7 @@ struct ResultsClass : ClassDefinition<T, realm::js::Results<T>, CollectionClass<
     static void filtered(ContextType, ObjectType, Arguments, ReturnValue &);
     static void sorted(ContextType, ObjectType, Arguments, ReturnValue &);
     static void is_valid(ContextType, ObjectType, Arguments, ReturnValue &);
+    static void is_empty(ContextType, ObjectType, Arguments, ReturnValue &);
 #if REALM_ENABLE_SYNC
     static void subscribe(ContextType, ObjectType, Arguments, ReturnValue &);
 #endif
@@ -115,6 +116,7 @@ struct ResultsClass : ClassDefinition<T, realm::js::Results<T>, CollectionClass<
         {"filtered", wrap<filtered>},
         {"sorted", wrap<sorted>},
         {"isValid", wrap<is_valid>},
+        {"isEmpty", wrap<is_empty>},
 #if REALM_ENABLE_SYNC
         {"subscribe", wrap<subscribe>},
 #endif
@@ -283,6 +285,11 @@ void ResultsClass<T>::is_valid(ContextType ctx, ObjectType this_object, Argument
     return_value.set(get_internal<T, ResultsClass<T>>(this_object)->is_valid());
 }
 
+template<typename T>
+void ResultsClass<T>::is_empty(ContextType ctx, ObjectType this_object, Arguments args, ReturnValue &return_value) {
+    return_value.set(get_internal<T, ResultsClass<T>>(this_object)->size() == 0);
+}
+
 #if REALM_ENABLE_SYNC
 template<typename T>
 void ResultsClass<T>::subscribe(ContextType ctx, ObjectType this_object, Arguments args, ReturnValue &return_value) {

tests/js/list-tests.js

@@ -1002,6 +1002,28 @@ module.exports = {
         TestCase.assertThrowsContaining(() => list.length, 'invalidated');
     },
 
+    testIsEmpty: function () {
+        const realm = new Realm({ schema: [schemas.PersonObject, schemas.PersonList] });
+        let object;
+        realm.write(() => {
+            object = realm.create('PersonList', {
+                list: [
+                ]
+            });
+        });
+        TestCase.assertTrue(object.list.isEmpty());
+
+        realm.write(() => {
+            object.list = [
+                { name: 'Bob', age: 42 },
+                { name: 'Alice', age: 42 }
+            ]
+        });
+        TestCase.assertFalse(object.list.isEmpty());
+
+        realm.close();
+    },
+
     testListAggregateFunctions: function() {
         const NullableBasicTypesList = {
             name: 'NullableBasicTypesList',
@@ -1301,5 +1323,5 @@ module.exports = {
         TestCase.assertEqual(objects[1].list1[0], "Foo");
         TestCase.assertEqual(objects[1].list2.length, 1);
         TestCase.assertEqual(objects[1].list2[0], "Bar");
-    }
+    },
 };

tests/js/results-tests.js

@@ -334,6 +334,17 @@ module.exports = {
         });
     },
 
+    testIsEmpty: function () {
+        let realm = new Realm({ schema: [schemas.TestObject] });
+        let result = realm.objects('TestObject');
+        TestCase.assertTrue(result.isEmpty());
+        realm.write(function () {
+            realm.create('TestObject', { doubleCol: 42 });
+        });
+        TestCase.assertFalse(result.isEmpty());
+        realm.close();
+    },
+
     testResultsDeletedObjects: function() {
         var realm = new Realm({schema: [schemas.TestObject]});