Added support for in-memory realms (#1304)

* Added support for in-memory realms

CHANGELOG.md

@@ -9,6 +9,7 @@ X.Y.Z Release notes
 * Added additional parameter for `Realm.open` and `Realm.openAsync` for download progress notifications 
 * Added `Realm.deleteFile` for deleting a Realm (#363).
 * Added `Realm.deleteModel` for deleting a Realm model in a migration (#573).
+* Added support for in-memory Realms.
 * `Realm.Sync.User.login`, `Realm.Sync.User.register`, and `Realm.Sync.User.registerWithProvider` return Promises and deprecate the callback style for them. Callbacks will continue to work for backward compatibility.
 
 ### Bug fixes

docs/realm.js

@@ -278,6 +278,11 @@ Realm.defaultPath;
  *   will be skipped if another process is accessing it.
  * @property {string} [path={@link Realm.defaultPath}] - The path to the file where the
  *   Realm database should be stored.
+ * @property {boolean} [inMemory=false] - Specifies if this Realm should be opened in-memory. This
+ *    still requires a path (can be the default path) to identify the Realm so other processes can
+ *    open the same Realm. The file will also be used as swap space if the Realm becomes bigger than
+ *    what fits in memory, but it is not persistent and will be removed when the last instance
+ *    is closed.
  * @property {boolean} [readOnly=false] - Specifies if this Realm should be opened as read-only.
  * @property {Array<Realm~ObjectClass|Realm~ObjectSchema>} [schema] - Specifies all the
  *   object types in this Realm. **Required** when first creating a Realm at this `path`.

lib/browser/index.js

@@ -55,6 +55,7 @@ function setupRealm(realm, realmId) {
         'empty',
         'path',
         'readOnly',
+        'inMemory',
         'schema',
         'schemaVersion',
         'syncSession',

lib/index.d.ts

@@ -80,6 +80,7 @@ declare namespace Realm {
         shouldCompactOnLaunch?: (totalBytes: number, usedBytes: number) => boolean;
         path?: string;
         readOnly?: boolean;
+        inMemory?: boolean;
         schema?: ObjectClass[] | ObjectSchema[];
         schemaVersion?: number;
         sync?: Realm.Sync.SyncConfiguration;

src/js_realm.hpp

@@ -187,6 +187,7 @@ public:
     static void get_path(ContextType, ObjectType, ReturnValue &);
     static void get_schema_version(ContextType, ObjectType, ReturnValue &);
     static void get_schema(ContextType, ObjectType, ReturnValue &);
+    static void get_in_memory(ContextType, ObjectType, ReturnValue &);
     static void get_read_only(ContextType, ObjectType, ReturnValue &);
     static void get_is_in_transaction(ContextType, ObjectType, ReturnValue &);
 #if REALM_ENABLE_SYNC
@@ -243,6 +244,7 @@ public:
         {"path", {wrap<get_path>, nullptr}},
         {"schemaVersion", {wrap<get_schema_version>, nullptr}},
         {"schema", {wrap<get_schema>, nullptr}},
+        {"inMemory", {wrap<get_in_memory>, nullptr}},
         {"readOnly", {wrap<get_read_only>, nullptr}},
         {"isInTransaction", {wrap<get_is_in_transaction>, nullptr}},
 #if REALM_ENABLE_SYNC
@@ -380,6 +382,12 @@ void RealmClass<T>::constructor(ContextType ctx, ObjectType this_object, size_t
             else if (config.path.empty()) {
                 config.path = js::default_path();
             }
+            
+            static const String in_memory_string = "inMemory";
+            ValueType in_memory_value = Object::get_property(ctx, object, in_memory_string);
+            if (!Value::is_undefined(ctx, in_memory_value) && Value::validated_to_boolean(ctx, in_memory_value, "inMemory")) {
+                config.in_memory = true;
+            }
 
             static const String read_only_string = "readOnly";
             ValueType read_only_value = Object::get_property(ctx, object, read_only_string);
@@ -606,6 +614,11 @@ void RealmClass<T>::get_schema(ContextType ctx, ObjectType object, ReturnValue &
     return_value.set(Schema<T>::object_for_schema(ctx, schema));
 }
 
+template<typename T>
+void RealmClass<T>::get_in_memory(ContextType ctx, ObjectType object, ReturnValue &return_value) {
+    return_value.set(get_internal<T, RealmClass<T>>(object)->get()->config().in_memory);
+}
+
 template<typename T>
 void RealmClass<T>::get_read_only(ContextType ctx, ObjectType object, ReturnValue &return_value) {
     return_value.set(get_internal<T, RealmClass<T>>(object)->get()->config().read_only());

tests/js/realm-tests.js

@@ -161,6 +161,36 @@ module.exports = {
             }]});
         }, "Property 'InvalidObject.link' declared as origin of linking objects property 'InvalidObject.linkingObjects' links to type 'IntObject'")
     },
+    
+    testRealmConstructorInMemory: function() {
+        // open in-memory realm instance
+        const realm1 = new Realm({inMemory: true, schema: [schemas.TestObject]});
+        realm1.write(function() {
+            realm1.create('TestObject', [1])
+        });
+        TestCase.assertEqual(realm1.inMemory, true);
+
+        // open a second instance of the same realm and check that they share data
+        const realm2 = new Realm({inMemory: true});
+        const objects = realm2.objects('TestObject');
+        TestCase.assertEqual(objects.length, 1);
+        TestCase.assertEqual(objects[0].doubleCol, 1.0);
+        TestCase.assertEqual(realm2.inMemory, true);
+
+        // Close both realms (this should delete the realm since there are no more
+        // references to it.
+        realm1.close();
+        realm2.close();
+
+        // Open the same in-memory realm again and verify that it is now empty
+        const realm3 = new Realm({inMemory: true});
+        TestCase.assertEqual(realm3.schema.length, 0);
+        
+        // try to open the same realm in persistent mode (should fail as you cannot mix modes)
+        TestCase.assertThrows(function() {
+            const realm4 = new Realm({});
+        });
+    },
 
     testRealmConstructorReadOnly: function() {
         var realm = new Realm({schema: [schemas.TestObject]});