diff --git a/packages/repository/src/model.ts b/packages/repository/src/model.ts
index 96e595cb88fc..dc953a6afb07 100644
--- a/packages/repository/src/model.ts
+++ b/packages/repository/src/model.ts
@@ -106,7 +106,9 @@ export class ModelDefinition {
     if (ids) {
       return ids.map(id => this.properties[id]);
     }
-    return Object.values(this.properties).filter(prop => prop.id);
+    const idProps = Object.keys(this.properties)
+      .map(p => this.properties[p]).filter(prop => prop.id);
+    return idProps;
   }
 }
 
@@ -122,7 +124,8 @@ export abstract class Model {
    */
   toJSON(): Object {
     const json: AnyObject = {};
-    for (const p in this.definition.properties) {
+    const def = (<typeof Model> this.constructor).definition;
+    for (const p in def.properties) {
       if (p in this) {
         json[p] = this[p];
       }
@@ -134,12 +137,14 @@ export abstract class Model {
    * Convert to a plain object as DTO
    */
   toObject(options?: Options): Object {
-    const obj: AnyObject = {};
-    if (options && options.ignoreUnknownProperties === false)
-    for (const p in this.definition.properties) {
-      if (p in this) {
+    let obj: AnyObject;
+    if (options && options.ignoreUnknownProperties === false) {
+      obj = {};
+      for (const p in this) {
         obj[p] = this[p];
       }
+    } else {
+      obj = this.toJSON();
     }
     return obj;
   }
@@ -200,9 +205,10 @@ export abstract class Entity extends Model implements Persistable {
     const idProps = this.definition.idProperties();
     if (idProps.length === 1) {
       where[idProps[0].name] = id;
-    }
-    for (const idProp of idProps) {
-      where[idProp.name] = id[idProp.name];
+    } else {
+      for (const idProp of idProps) {
+        where[idProp.name] = id[idProp.name];
+      }
     }
     return where;
   }
diff --git a/packages/repository/test/unit/decorator/model-and-relation.ts b/packages/repository/test/unit/decorator/model-and-relation.ts
index d9ef5a541f12..ee814ef4c545 100644
--- a/packages/repository/test/unit/decorator/model-and-relation.ts
+++ b/packages/repository/test/unit/decorator/model-and-relation.ts
@@ -6,7 +6,7 @@
 import { expect } from '@loopback/testlab';
 import { model, property, MODEL_KEY, PROPERTY_KEY }
   from '../../../src/decorators/model';
-import { belongsTo, embedsOne, embedsMany, hasMany, referencesMany,
+import { relation, hasOne, belongsTo, embedsOne, embedsMany, hasMany, referencesMany,
   referencesOne, RELATION_KEY, RelationType } from '../../../src/decorators/relation';
 
 import { Entity, ValueObject } from '../../../src/model';
@@ -40,8 +40,27 @@ describe('model decorator', () => {
     description: string;
   }
 
+  interface ICustomer {}
+
+  @model({ name: 'order' })
+  class Order extends Entity {
+    @property({
+      name: 'qty', mysql: {
+        column: 'QTY',
+      },
+    })
+    quantity: number;
+
+    @property({ name: 'id', id: true, generated: true })
+    id: string;
+    customerId: string;
+
+    @belongsTo({ target: 'Customer' })
+    customer: ICustomer; // TypeScript does not allow me to reference Customer here
+  }
+
   @model()
-  class Customer extends Entity {
+  class Customer extends Entity implements ICustomer {
     id: string;
     email: string;
     firstName: string;
@@ -61,23 +80,12 @@ describe('model decorator', () => {
 
     @hasMany()
     orders?: Order[];
-  }
-
-  @model({ name: 'order' })
-  class Order extends Entity {
-    @property({
-      name: 'qty', mysql: {
-        column: 'QTY',
-      },
-    })
-    quantity: number;
 
-    @property({ name: 'id', id: true, generated: true })
-    id: string;
-    customerId: string;
+    @hasOne()
+    lastOrder?: Order;
 
-    @belongsTo({ target: 'Customer' })
-    customer: Customer;
+    @relation({type: RelationType.hasMany})
+    recentOrders?: Order[];
   }
 
   // Skip the tests before we resolve the issue around global `Reflector`
@@ -139,4 +147,18 @@ describe('model decorator', () => {
     });
   });
 
+  it('adds hasOne metadata', () => {
+    const meta = Reflector.getOwnMetadata(RELATION_KEY, Customer.prototype, 'lastOrder');
+    expect(meta).to.eql({
+      type: RelationType.hasOne,
+    });
+  });
+
+  it('adds relation metadata', () => {
+    const meta = Reflector.getOwnMetadata(RELATION_KEY, Customer.prototype, 'recentOrders');
+    expect(meta).to.eql({
+      type: RelationType.hasMany,
+    });
+  });
+
 });
diff --git a/packages/repository/test/unit/model/model.ts b/packages/repository/test/unit/model/model.ts
index 5484fb2647a3..1ff9fd315711 100644
--- a/packages/repository/test/unit/model/model.ts
+++ b/packages/repository/test/unit/model/model.ts
@@ -9,22 +9,118 @@ import { Model, Entity, ModelDefinition, PropertyDefinition } from '../../../src
 
 describe('model', () => {
 
+  const customerDef = new ModelDefinition('Customer');
+  customerDef.addProperty(new PropertyDefinition('id', 'string'))
+    .addProperty('email', 'string').addProperty('firstName', String)
+    .addProperty('lastName', STRING)
+    .addSetting('id', 'id');
+
+  const relamCustomerDef = new ModelDefinition('RealmCustomer');
+  relamCustomerDef.addProperty(new PropertyDefinition('realm', 'string'))
+    .addProperty('email', 'string').addProperty('firstName', String)
+    .addProperty('lastName', STRING)
+    .addSetting('id', ['realm', 'email']);
+
+  const userDef = new ModelDefinition('User');
+  const idProp = new PropertyDefinition('id', 'string');
+  idProp.id = true;
+  userDef.addProperty(idProp)
+    .addProperty('email', 'string').addProperty('firstName', String)
+    .addProperty('lastName', STRING);
+
+  class Customer extends Entity {
+    static modelName = 'Customer';
+    static definition = customerDef;
+  }
+
+  class RealmCustomer extends Entity {
+    static modelName = 'RealmCustomer';
+    static definition = relamCustomerDef;
+  }
+
+  class User extends Entity {
+    static modelName = 'User';
+    static definition = userDef;
+  }
+
+  function createCustomer() {
+    const customer = new Customer();
+    customer.id = '123';
+    customer.email = 'xyz@example.com';
+    return customer;
+  }
+
+  function createRealmCustomer() {
+    const customer = new RealmCustomer();
+    customer.realm = 'org1';
+    customer.email = 'xyz@example.com';
+    return customer;
+  }
+
   it('adds properties', () => {
-    const modelDef = new ModelDefinition('Customer');
-    modelDef.addProperty(new PropertyDefinition('id', 'string'))
-      .addProperty('email', 'string').addProperty('firstName', String)
-      .addProperty('lastName', STRING)
-      .addSetting('key', ['id']);
-    expect(modelDef.name).to.eql('Customer');
-    expect(modelDef.properties).have.properties('id', 'email', 'lastName', 'firstName');
-    expect(modelDef.properties.lastName).to.eql(
+    expect(customerDef.name).to.eql('Customer');
+    expect(customerDef.properties).have.properties('id', 'email', 'lastName', 'firstName');
+    expect(customerDef.properties.lastName).to.eql(
       new PropertyDefinition('lastName', STRING));
   });
 
-  /*
-  class CustomerModel extends Entity {
-    static modelName = 'Customer';
-    static definition = modelDef;
-  }
-  */
+  it('adds settings', () => {
+    expect(customerDef.settings).have.property('id', 'id');
+  });
+
+  it('lists id properties', () => {
+    expect(customerDef.idProperties()).to.eql([customerDef.properties.id]);
+    expect(userDef.idProperties()).to.eql([userDef.properties.id]);
+    expect(relamCustomerDef.idProperties()).to.eql([
+        relamCustomerDef.properties.realm,
+        relamCustomerDef.properties.email,
+      ]);
+  });
+
+  it('converts to json', () => {
+    const customer = createCustomer();
+    expect(customer.toJSON()).to.eql({ id: '123', email: 'xyz@example.com' });
+  });
+
+  it('converts to plain object', () => {
+    const customer = createCustomer();
+    customer.unknown = 'abc';
+    expect(customer.toObject()).to.eql({ id: '123', email: 'xyz@example.com' });
+    expect(customer.toObject({ignoreUnknownProperties: false}))
+      .to.eql({ id: '123', email: 'xyz@example.com', unknown: 'abc' });
+  });
+
+  it('gets id', () => {
+    const customer = createCustomer();
+    expect(customer.getId()).to.eql('123');
+  });
+
+  it('gets id object', () => {
+    const customer = createCustomer();
+    expect(customer.getIdObject()).to.eql({id: '123'});
+  });
+
+  it('builds where for id', () => {
+    const where = Customer.buildWhereForId('123');
+    expect(where).to.eql({id: '123'});
+  });
+
+  it('gets composite id', () => {
+    const customer = createRealmCustomer();
+    expect(customer.getId()).to.eql(
+      {realm: 'org1', email: 'xyz@example.com'});
+  });
+
+  it('gets composite id object', () => {
+    const customer = createRealmCustomer();
+    expect(customer.getIdObject()).to.eql(
+      {realm: 'org1', email: 'xyz@example.com'});
+  });
+
+  it('builds where for composite id', () => {
+    const where = RealmCustomer.buildWhereForId(
+      {realm: 'org1', email: 'xyz@example.com'});
+    expect(where).to.eql({realm: 'org1', email: 'xyz@example.com'});
+  });
+
 });