MVC Design Pattern on Salesforce

MVC Design Pattern on Salesforce – Complete Guide for Platform Developer 1 Exam

Introduction

The Model-View-Controller (MVC) design pattern is one of the foundational architectural concepts tested on the Salesforce Platform Developer 1 (PD1) exam. Understanding how Salesforce implements MVC is critical because it shapes how you build applications, organize code, and separate concerns on the platform. Questions on this topic appear regularly, and a strong grasp of MVC ensures you can correctly identify which Salesforce component belongs to which layer.

Why Is the MVC Design Pattern Important?

The MVC pattern is important for several reasons:

1. Separation of Concerns: MVC divides an application into three interconnected layers, each responsible for a distinct aspect of the application. This makes code easier to maintain, test, and scale.

2. Reusability: Because the business logic (Model), user interface (View), and application logic (Controller) are separated, each component can be reused or modified independently without breaking the others.

3. Salesforce Platform Alignment: Salesforce was designed with MVC principles at its core. Understanding MVC helps developers work with the platform rather than against it, leveraging declarative and programmatic tools in the right places.

4. Team Collaboration: When layers are clearly separated, different team members (administrators, developers, UI designers) can work on different layers simultaneously.

5. Exam Relevance: Salesforce expects developers to know which platform components map to which MVC layer, and how they interact.

What Is the MVC Design Pattern?

MVC stands for Model-View-Controller. It is a software architectural pattern that separates an application into three main logical components:

1. Model (Data Layer)
The Model represents the data and the business logic of the application. It is responsible for managing the data, rules, and logic. In a traditional application, this includes the database schema, data access logic, and business rules.

2. View (Presentation Layer)
The View is responsible for the user interface — what the user sees and interacts with. It displays data from the Model to the user and sends user commands to the Controller.

3. Controller (Application Logic Layer)
The Controller acts as the intermediary between the Model and the View. It receives input from the View, processes it (often by interacting with the Model), and returns the output to the View. It contains the application logic that coordinates how data flows between the Model and View.

How MVC Works on the Salesforce Platform

Salesforce implements MVC through both declarative (clicks) and programmatic (code) tools. Here is how each layer maps to Salesforce components:

Model (Data Layer) on Salesforce:

The Model layer in Salesforce encompasses everything related to data storage, data structure, and business rules applied to data. Key components include:

• Standard and Custom Objects: These are the database tables. Objects like Account, Contact, Opportunity, and any custom objects you create (e.g., Invoice__c) form the data model.
• Fields: Standard and custom fields on objects define the schema — what data is stored and in what format.
• Relationships: Lookup, Master-Detail, and Junction relationships define how objects relate to each other.
• Validation Rules: These enforce data integrity by ensuring data meets certain criteria before it can be saved.
• Workflow Rules and Process Builder (data-focused automations): When they update fields or enforce rules, they act on the Model.
• Apex Classes (business logic): Apex classes that contain business rules, data manipulation, and SOQL/SOSL queries operate on the Model layer. For example, a trigger handler class that enforces a business rule is part of the Model.
• Apex Triggers: Triggers fire on DML operations and enforce business logic, placing them in the Model layer.

View (Presentation Layer) on Salesforce:

The View layer includes everything the user sees and interacts with:

• Lightning Pages: App pages, record pages, and home pages built in Lightning App Builder.
• Lightning Web Components (LWC) — HTML/CSS portion: The template files (.html) and styling (.css) of LWC are the View.
• Aura Components — Markup portion: The .cmp markup files in Aura components represent the View.
• Visualforce Pages: The .page files that define the UI markup are the View layer.
• Page Layouts: Declarative page layouts that control how fields and related lists appear on record detail pages.
• Lightning Record Pages and Compact Layouts: These control the presentation of data.
• Reports and Dashboards: These are visual representations of data and belong to the View.
• Tabs: Tabs provide navigation to objects and pages, which is part of the View.

Controller (Application Logic Layer) on Salesforce:

The Controller layer bridges the Model and View. It processes user actions and determines what data to fetch or update:

• Standard Controllers: Salesforce provides built-in controllers for every standard and custom object. These automatically provide CRUD functionality to Visualforce pages without writing code.
• Custom Controllers (Apex): Apex classes written to replace the standard controller entirely, providing complete control over page behavior.
• Controller Extensions (Apex): Apex classes that extend the functionality of standard or custom controllers, adding additional logic.
• Lightning Web Components — JavaScript portion: The .js files in LWC handle user interactions, call Apex methods, and manage component state. This is the Controller.
• Aura Components — JavaScript Controllers and Helpers: The controller.js and helper.js files in Aura handle events and logic.
• Apex Controllers called via @AuraEnabled: Apex methods exposed to Lightning components act as server-side controllers.

Summary Table: Salesforce MVC Mapping

Model: Objects, Fields, Relationships, Schema, Apex Triggers, Apex Classes (business logic), Validation Rules, SOQL/SOSL Queries
View: Visualforce Pages, Lightning Pages, LWC Templates (HTML/CSS), Aura Markup (.cmp), Page Layouts, Reports, Dashboards, Tabs
Controller: Standard Controllers, Custom Controllers, Controller Extensions, LWC JavaScript (.js), Aura JavaScript Controllers/Helpers, @AuraEnabled Apex Methods

How the Layers Interact on Salesforce

Here is a typical flow:

1. A user interacts with a Lightning Web Component (View) — for example, clicking a button.
2. The button click triggers a JavaScript function in the LWC's .js file (Controller).
3. The JavaScript calls an @AuraEnabled Apex method (Controller/Model bridge).
4. The Apex method runs a SOQL query against Custom Objects (Model) and applies business logic.
5. The results are returned to the LWC JavaScript (Controller), which updates the component's properties.
6. The LWC HTML template (View) reactively re-renders to display the updated data to the user.

Important Nuances for the Exam

• Apex Triggers are part of the Model layer because they operate on data events (before/after insert, update, delete, etc.) and enforce business rules directly on data.
• Validation Rules are part of the Model because they enforce data integrity at the data layer.
• Visualforce Pages are the View. The Visualforce Controller (standard, custom, or extension) is the Controller. Do not confuse the two.
• Standard Controllers are provided automatically by Salesforce for each object. They provide default CRUD behavior. You do NOT need to write code for them.
• Controller Extensions extend (not replace) a standard or custom controller. They add functionality while preserving existing behavior.
• In Lightning Web Components, the HTML file is the View and the JavaScript file is the Controller. The data retrieved from Apex or the wire service is the Model.
• The database schema (objects and fields) is always the Model, regardless of whether it was created declaratively or programmatically.

Common Exam Scenarios

Scenario 1: A question asks which layer a Visualforce page belongs to. Answer: View.

Scenario 2: A question asks where business logic (such as calculating a discount) should reside. Answer: Model layer — in Apex classes or triggers.

Scenario 3: A question asks what a Standard Controller provides. Answer: It provides default CRUD (Create, Read, Update, Delete) functionality for a single record and belongs to the Controller layer.

Scenario 4: A question describes a page layout that controls field visibility. Answer: View layer.

Scenario 5: A question asks about the JavaScript file in an LWC. Answer: Controller layer.

Exam Tips: Answering Questions on MVC Design Pattern on Salesforce

1. Memorize the Mapping: Know exactly which Salesforce components belong to Model, View, and Controller. This is the most commonly tested aspect. Create flashcards if needed: Objects/Fields/Triggers/Validation Rules = Model; Pages/Layouts/Templates = View; Controllers/JS Files/Extensions = Controller.

2. Look for Keywords in Questions: If a question mentions data storage, schema, fields, objects, relationships, business rules, triggers, or validation rules, think Model. If it mentions user interface, pages, layouts, what the user sees, HTML, or visual elements, think View. If it mentions handling user input, processing logic, coordinating between data and UI, JavaScript handlers, or Apex controllers, think Controller.

3. Understand Controller Types: The exam may test the difference between Standard Controllers, Custom Controllers, and Controller Extensions. Remember: Standard Controllers are automatic and provide basic CRUD. Custom Controllers replace the standard controller entirely. Extensions add to an existing controller (standard or custom).

4. Don't Overthink Hybrid Components: Some Salesforce features span multiple layers (e.g., an Apex class may contain both business logic and controller logic). In exam questions, focus on the primary purpose described in the question. If the question emphasizes data manipulation, it's Model. If it emphasizes responding to user actions, it's Controller.

5. Remember Declarative vs. Programmatic: MVC applies to both declarative and programmatic development. Page Layouts (declarative) are View. Validation Rules (declarative) are Model. The exam may test your understanding of MVC across both paradigms.

6. Watch for Trick Answers: The exam may offer answer choices that mix up layers. For example, it might say a Visualforce page is the Controller or that a trigger is the View. Stay focused on what each component actually does — a Visualforce page displays data (View), while a trigger operates on data events (Model).

7. Understand the Purpose of Separation: Some questions may ask why MVC is used rather than what it is. Key benefits to remember: maintainability, reusability, testability, parallel development, and clear separation of concerns.

8. Practice with Real Examples: Think about a real Salesforce application you've built or studied. Identify which parts are Model, View, and Controller. This concrete understanding will help you answer abstract exam questions more confidently.

9. Eliminate Wrong Answers First: On multiple-choice questions, eliminate any answer that clearly places a component in the wrong layer. This narrows your options and increases your chances even if you're unsure about the correct answer.

10. Time Management: MVC questions are typically straightforward if you know the mapping. Don't spend too much time on them. Answer quickly and confidently, then move on to more complex questions.

Final Summary

The MVC design pattern on Salesforce is about understanding which platform components handle data (Model), presentation (View), and application logic (Controller). The Salesforce platform naturally enforces this separation through its architecture — objects and triggers handle data, pages and components handle UI, and controllers and JavaScript handle the logic in between. Mastering this mapping is essential for the PD1 exam and for building well-architected Salesforce applications.