diff --git a/integration-tests/tests/src/objects.ts b/integration-tests/tests/src/objects.ts
index 317a5c7864..aeee8a4b18 100644
--- a/integration-tests/tests/src/objects.ts
+++ b/integration-tests/tests/src/objects.ts
@@ -1,33 +1,239 @@
 import { expect } from "chai";
-
-import { IPerson, PersonSchema } from "./schemas/person-and-dogs";
+import {
+    IPerson as IPersonWithId,
+    Person as PersonWithId,
+    PersonSchema as PersonSchemaWithId
+} from "./schemas/person-and-dog-with-primary-ids";
+import { IPerson, Person, PersonSchema } from "./schemas/person-and-dogs";
 
 describe("Realm objects", () => {
-    it("can be created", () => {
-        const realm = new Realm({ schema: [PersonSchema] });
-        let john: IPerson;
-        realm.write(() => {
-            john = realm.create<IPerson>("Person", {
-                name: "John Doe",
-                age: 42
-            });
-        });
-        // Expect John to be the one and only result
-        const persons = realm.objects("Person");
-        expect(persons.length).equals(1);
-        const [firstPerson] = persons;
-        expect(firstPerson).deep.equals(john);
+    describe("Interface & object literal", () => {
+        it("can be created", () => {
+            const realm = new Realm({ schema: [PersonSchema] });
+            let john: IPerson;
+
+            realm.write(() => {
+                john = realm.create<IPerson>(PersonSchema.name, {
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+
+            // Expect John to be the one and only result
+            const persons = realm.objects(PersonSchema.name);
+            expect(persons.length).equals(1);
+            const [firstPerson] = persons;
+            expect(firstPerson).deep.equals(john);
+        });
+
+        it("can have it's properties read", () => {
+            const realm = new Realm({ schema: [PersonSchema] });
+            let john: IPerson;
+
+            realm.write(() => {
+                john = realm.create<IPerson>(PersonSchema.name, {
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(42);
+        });
+
+        it("can be fetched with objectForPrimaryKey", () => {
+            const realm = new Realm({ schema: [PersonSchemaWithId] });
+            const _id = "0e19bcb8-c77a-44e5-9713-d6a59702869f";
+
+            realm.write(() => {
+                realm.create<PersonWithId>(PersonSchemaWithId.name, {
+                    _id,
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+
+            const john = realm.objectForPrimaryKey<IPersonWithId>(
+                PersonSchemaWithId.name,
+                _id
+            );
+
+            expect(john).instanceOf(Realm.Object);
+            expect(john._id).equals(_id);
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(42);
+        });
+
+        it("can be updated", () => {
+            const realm = new Realm({ schema: [PersonSchemaWithId] });
+            let john: IPersonWithId;
+            const _id = "8ef4d2e2-a8be-468d-995d-36068d15b520";
+
+            realm.write(() => {
+                john = realm.create<IPersonWithId>(PersonSchemaWithId.name, {
+                    _id,
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(42);
+
+            realm.write(() => {
+                realm.create<IPersonWithId>(
+                    PersonSchemaWithId.name,
+                    { _id, age: 43 },
+                    Realm.UpdateMode.All
+                );
+            });
+
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(43);
+
+            const update: Partial<IPersonWithId> = {
+                _id,
+                name: "Mr. John Doe"
+            };
+
+            realm.write(() => {
+                realm.create<IPersonWithId>(
+                    PersonSchemaWithId.name,
+                    update,
+                    Realm.UpdateMode.Modified
+                );
+            });
+
+            expect(john.name).equals("Mr. John Doe");
+            expect(john.age).equals(43);
+
+            expect(() =>
+                realm.write(() => {
+                    realm.create<IPersonWithId>(
+                        PersonSchemaWithId.name,
+                        { _id, name: "John Doe", age: 42 },
+                        Realm.UpdateMode.Never
+                    );
+                })
+            ).throws(
+                `Attempting to create an object of type '${
+                    PersonSchemaWithId.name
+                }' with an existing primary key value ''${_id}''.`
+            );
+
+            // Excpect only one instance of 'PersonSchemaWithId' in db after all updates
+            const persons = realm.objects(PersonSchemaWithId.name);
+            expect(persons.length).equals(1);
+        });
     });
 
-    it("can have it's properties read", () => {
-        const realm = new Realm({ schema: [PersonSchema] });
-        realm.write(() => {
-            const john = realm.create<IPerson>("Person", {
-                name: "John Doe",
-                age: 42
+    describe("Class Model", () => {
+        it("can be created", () => {
+            const realm = new Realm({ schema: [Person] });
+            let john: Person;
+
+            realm.write(() => {
+                john = realm.create(Person, {
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+            // Expect John to be the one and only result
+            const persons = realm.objects(Person);
+            expect(persons.length).equals(1);
+            const [firstPerson] = persons;
+            expect(firstPerson).deep.equals(john);
+            expect(firstPerson).instanceOf(Person);
+        });
+
+        it("can have it's properties read", () => {
+            const realm = new Realm({ schema: [Person] });
+            realm.write(() => {
+                const john = realm.create(Person, {
+                    name: "John Doe",
+                    age: 42
+                });
+                expect(john.name).equals("John Doe");
+                expect(john.age).equals(42);
+            });
+        });
+
+        it("can be fetched with objectForPrimaryKey", () => {
+            const realm = new Realm({ schema: [PersonWithId] });
+            const _id = "1d84d60b-8c64-4531-bfdc-87cdd9e029c3";
+
+            realm.write(() => {
+                realm.create(PersonWithId, {
+                    _id,
+                    name: "John Doe",
+                    age: 42
+                });
+            });
+
+            const john = realm.objectForPrimaryKey(PersonWithId, _id);
+
+            expect(john).instanceOf(PersonWithId);
+            expect(john._id).equals(_id);
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(42);
+        });
+
+        it("can be updated", () => {
+            const realm = new Realm({ schema: [PersonWithId] });
+            let john: PersonWithId;
+            const _id = "e4762cd3-b92f-47ae-857a-26eba201e7db";
+
+            realm.write(() => {
+                john = realm.create(PersonWithId, {
+                    _id,
+                    name: "John Doe",
+                    age: 42
+                });
             });
+
             expect(john.name).equals("John Doe");
             expect(john.age).equals(42);
+
+            realm.write(() => {
+                realm.create(
+                    PersonWithId,
+                    { _id, age: 43 },
+                    Realm.UpdateMode.All
+                );
+            });
+
+            expect(john.name).equals("John Doe");
+            expect(john.age).equals(43);
+
+            const update: Partial<PersonWithId> = {
+                _id,
+                name: "Mr. John Doe"
+            };
+
+            realm.write(() => {
+                realm.create(PersonWithId, update, Realm.UpdateMode.Modified);
+            });
+
+            expect(john.name).equals("Mr. John Doe");
+            expect(john.age).equals(43);
+
+            expect(() =>
+                realm.write(() => {
+                    realm.create(
+                        PersonWithId,
+                        { _id, name: "John Doe", age: 42 },
+                        Realm.UpdateMode.Never
+                    );
+                })
+            ).throws(
+                `Attempting to create an object of type '${
+                    PersonWithId.schema.name
+                }' with an existing primary key value ''${_id}''.`
+            );
+
+            // Excpect only one instance of 'PersonWithId' in db after all updates
+            const persons = realm.objects(PersonWithId);
+            expect(persons.length).equals(1);
         });
     });
 });
diff --git a/integration-tests/tests/src/serialization.ts b/integration-tests/tests/src/serialization.ts
index 9af9ee5030..513e989ce0 100755
--- a/integration-tests/tests/src/serialization.ts
+++ b/integration-tests/tests/src/serialization.ts
@@ -261,8 +261,9 @@ describe("JSON serialization", () => {
                 });
 
                 it("throws correct error on serialization", () => {
-                    expect(() => JSON.stringify(persons[0])).throws(
-                        "Converting circular structure to JSON"
+                    expect(() => JSON.stringify(persons)).throws(
+                        TypeError,
+                        /circular|cyclic/i
                     );
                 });
 
@@ -291,7 +292,8 @@ describe("JSON serialization", () => {
 
                 it("throws correct error on serialization", () => {
                     expect(() => JSON.stringify(persons)).throws(
-                        "Converting circular structure to JSON"
+                        TypeError,
+                        /circular|cyclic/i
                     );
                 });
 
diff --git a/lib/index.d.ts b/lib/index.d.ts
index 68f7e9b477..315b9168d3 100644
--- a/lib/index.d.ts
+++ b/lib/index.d.ts
@@ -938,38 +938,40 @@ declare class Realm {
     /**
      * @param  {string} type
      * @param  {T} properties
-     * @param  {boolean} update?
+     * @param  {Realm.UpdateMode} mode? If not provided, `Realm.UpdateMode.Never` is used.
      * @returns T & Realm.Object
-     *
-     * @deprecated, to be removed in future versions. Use `create(type, properties, UpdateMode)` instead.
      */
-    create<T>(type: string, properties: RealmInsertionModel<T>, update?: boolean): T & Realm.Object
+    create<T>(type: string, properties: RealmInsertionModel<T>, mode?: Realm.UpdateMode.Never): T & Realm.Object;
+    create<T>(type: string, properties: Partial<T> | Partial<RealmInsertionModel<T>>, mode: Realm.UpdateMode.All | Realm.UpdateMode.Modified): T & Realm.Object;
 
     /**
-     * @param  {Class} type
+     * @param  {string} type
      * @param  {T} properties
      * @param  {boolean} update?
-     * @returns T
+     * @returns T & Realm.Object
      *
      * @deprecated, to be removed in future versions. Use `create(type, properties, UpdateMode)` instead.
      */
-    create<T extends Realm.Object>(type: {new(...arg: any[]): T; }, properties: RealmInsertionModel<T>, update?: boolean): T
+    create<T>(type: string, properties: RealmInsertionModel<T>, update: boolean): T & Realm.Object;
 
     /**
-     * @param  {string} type
+     * @param  {Class} type
      * @param  {T} properties
      * @param  {Realm.UpdateMode} mode? If not provided, `Realm.UpdateMode.Never` is used.
-     * @returns T & Realm.Object
+     * @returns T
      */
-    create<T>(type: string, properties: RealmInsertionModel<T>, mode?: Realm.UpdateMode): T & Realm.Object
+    create<T extends Realm.Object>(type: {new(...arg: any[]): T; }, properties: RealmInsertionModel<T>, mode?: Realm.UpdateMode.Never): T;
+    create<T extends Realm.Object>(type: {new(...arg: any[]): T; }, properties: Partial<T> | Partial<RealmInsertionModel<T>>, mode: Realm.UpdateMode.All | Realm.UpdateMode.Modified): T;
 
-    /**
+        /**
      * @param  {Class} type
      * @param  {T} properties
-     * @param  {Realm.UpdateMode} mode? If not provided, `Realm.UpdateMode.Never` is used.
+     * @param  {boolean} update?
      * @returns T
+     *
+     * @deprecated, to be removed in future versions. Use `create(type, properties, UpdateMode)` instead.
      */
-    create<T extends Realm.Object>(type: {new(...arg: any[]): T; }, properties: RealmInsertionModel<T>, mode?: Realm.UpdateMode): T
+    create<T extends Realm.Object>(type: {new(...arg: any[]): T; }, properties: RealmInsertionModel<T>, update: boolean): T
 
     /**
      * @param  {Realm.Object|Realm.Object[]|Realm.List<any>|Realm.Results<any>|any} object
@@ -988,18 +990,18 @@ declare class Realm {
     deleteAll(): void;
 
     /**
-     * @param  {string|Realm.ObjectType|Function} type
+     * @param  {string} type
      * @param  {number|string} key
      * @returns {T | undefined}
      */
-    objectForPrimaryKey<T>(type: string | Realm.ObjectType | Function, key: number | string): T & Realm.Object | undefined;
+    objectForPrimaryKey<T>(type: string, key: number | string): (T & Realm.Object) | undefined;
 
     /**
-     * @param  {string|Realm.ObjectType|Function} type
-     * @param  {string} id
+     * @param  {Class} type
+     * @param  {number|string} key
      * @returns {T | undefined}
      */
-    objectForPrimaryKey<T>(type: string | Realm.ObjectType | Function, id: string): T & Realm.Object | undefined;
+    objectForPrimaryKey<T extends Realm.Object>(type: {new(...arg: any[]): T; }, key: number | string): T | undefined;
 
     /**
      * @param  {string} type