Salesforce Integration Interview Questions

1What it is

Two directions. Into Salesforce: the REST, SOAP, Bulk and Composite APIs. Out of Salesforce: Apex callouts, Platform Events, Change Data Capture and outbound messages.

2Why it matters

The right choice depends on who starts the conversation, how much data moves, and how quickly it must arrive. A pattern picked for the wrong reason fails at volume or loses messages.

3Example

4In short - say this in the interview

1What it is

A Named Credential stores an external endpoint's URL, and - through its External Credential - how to authenticate to it. Apex then calls callout:Name instead of a hard-coded URL with a token.

2Why it matters

Secrets never live in code, sandboxes can point at a test endpoint without a code change, authentication (OAuth, API keys, JWT) is handled by the platform, and no Remote Site Setting is needed.

3Example

HttpRequest req = new HttpRequest();
req.setEndpoint('callout:Payments_API/v1/refunds');     // URL and auth live in the credential
req.setMethod('POST');
req.setHeader('Content-Type', 'application/json');
req.setBody(JSON.serialize(new Map<String, Object>{ 'orderId' => orderId, 'amount' => amount }));
req.setTimeout(20000);                                   // milliseconds; the default is 10 seconds

HttpResponse res = new Http().send(req);
if (res.getStatusCode() != 201) {
    throw new CalloutException('Refund failed: ' + res.getStatus());
}

4In short - say this in the interview

1What it is

Tests cannot make real callouts. You implement HttpCalloutMock with a fake response and register it with Test.setMock, so the code under test receives it instead of calling out.

2Why it matters

It makes tests fast and repeatable, and lets you test the failure paths - a 500, a timeout, a malformed body - that are hard to trigger against a real system.

3Example

@isTest
global class RefundMock implements HttpCalloutMock {
    global HttpResponse respond(HttpRequest req) {
        HttpResponse res = new HttpResponse();
        res.setStatusCode(201);
        res.setBody('{"status":"created"}');
        return res;
    }
}

@isTest
static void refundsAnOrder() {
    Test.setMock(HttpCalloutMock.class, new RefundMock());
    Test.startTest();
    RefundService.refund('ORD-1001', 499);
    Test.stopTest();
    // assert on what the service saved
}

4In short - say this in the interview

1What it is

A global class annotated @RestResource(urlMapping=...), with static methods marked @HttpGet, @HttpPost and so on. It is called at /services/apexrest/ followed by the mapping.

2Why it matters

The standard REST API exposes objects one at a time. A custom Apex REST endpoint lets an external system do one business operation - "create an order with its lines" - in a single call, with your validation.

3Example

@RestResource(urlMapping='/orders/*')
global with sharing class OrderApi {

    @HttpGet       // GET /services/apexrest/orders/ORD-1001
    global static Order__c getOrder() {
        String orderNo = RestContext.request.requestURI.substringAfterLast('/');
        return [SELECT Id, Name, Status__c FROM Order__c
                WHERE Name = :orderNo WITH USER_MODE LIMIT 1];
    }

    @HttpPost      // POST with a JSON body {"customerId": "...", "amount": 499}
    global static Id createOrder(String customerId, Decimal amount) {
        Order__c o = new Order__c(Customer__c = customerId, Amount__c = amount);
        insert o;
        return o.Id;
    }
}

4In short - say this in the interview

1What it is

Both publish events on the event bus. Platform Events are messages you define and publish yourself ("Order Shipped"). Change Data Capture publishes automatically whenever a record is created, updated, deleted or undeleted.

2Why it matters

Events decouple systems: the publisher does not know who listens, and subscribers can be added without touching it. Platform Events carry business meaning; CDC is for keeping another system's copy of the data in sync.

3Example

// Publish
Order_Shipped__e evt = new Order_Shipped__e(Order_Number__c = 'ORD-1001', Carrier__c = 'BlueDart');
Database.SaveResult r = EventBus.publish(evt);

// Subscribe
trigger OrderShippedListener on Order_Shipped__e (after insert) {
    for (Order_Shipped__e e : Trigger.new) { /* notify the customer ... */ }
}

4In short - say this in the interview

1What it is

The error raised when Apex makes a callout after DML in the same transaction. Salesforce will not hold database changes open while it waits on an external system.

2Why it matters

It shows up the moment a trigger tries to send a newly saved record to an ERP. The fix is to separate the save from the call - the callout happens in a transaction of its own, after the commit.

3Example

public class SyncOrderJob implements Queueable, Database.AllowsCallouts {
    private final Id orderId;
    public SyncOrderJob(Id orderId) { this.orderId = orderId; }

    public void execute(QueueableContext ctx) {
        // A new transaction, after the save committed - callouts are allowed here.
        OrderSync.send(orderId);
    }
}

// In the trigger handler, after the insert:
System.enqueueJob(new SyncOrderJob(order.Id));

4In short - say this in the interview

1What it is

External systems authenticate through a connected app (or an External Client App) using an OAuth 2.0 flow. The main ones: JWT bearer and client credentials for server-to-server, and web server (authorization code) when a person logs in.

2Why it matters

The flow decides whether a person must be present and where secrets live. Server-to-server integrations must not depend on someone typing a password, and should run as a dedicated integration user with only the access it needs.

3Example

4In short - say this in the interview