Comprehensive and Detailed Explanation From Exact Extract:

To determine the most efficient SOQL statement for retrieving Contact records where the related Account’s Industry is 'Technology', along with their associated Job_Application__c records, we need to analyze the object relationships, SOQL syntax, and relationship names. Let’s break down the problem and evaluate each option systematically, referencing Salesforce’s official documentation.

Understanding the Object Relationships:

Job_Application__c and Contact: The Job_Application__c custom object has a master-detail relationship with the Contact object, where Contact is the master. In a master-detail relationship, the child (Job_Application__c) records are dependent on the parent (Contact) records. The Salesforce Data Model documentation states: “In a master-detail relationship, the detail record inherits security and ownership from the master record” (Salesforce Object Reference Guide, Relationships).

Contact and Account: The Contact object has a standard lookup relationship with the Account object (via the AccountId field). This allows a Contact to be associated with an Account, and we can access Account fields in SOQL queries using the relationship name Account. The Salesforce Object Reference Guide confirms: “The AccountId field on Contact references the Account object, and the relationship name is Account” (Salesforce Object Reference Guide, Contact Object).

Requirement: The query must:

Retrieve Contact records where the related Account’s Industry field equals 'Technology'.

Include the related Job_Application__c records for each Contact.

Be efficient and syntactically correct based on Salesforce SOQL standards.

SOQL Relationship Query Basics:

Parent-to-Child Queries: To retrieve child records (Job_Application__c) along with parent records (Contact), we use a subquery in the SELECT clause with the relationship name. The Apex Developer Guide states: “For custom objects in a master-detail relationship, the relationship name for the child is typically the plural form of the object name with __r (e.g., Job_Applications__r)” (Salesforce Apex Developer Guide, SOQL Relationship Queries).

Accessing Parent Fields: To filter on a parent object’s field (e.g., Account’s Industry), we use the relationship name (e.g., Account.Industry). The SOQL and SOSL Reference Guide notes: “In a lookup relationship, use the parent object’s API name (e.g., Account) followed by the field name” (Salesforce SOQL and SOSL Reference Guide, Relationship Queries).

Efficiency: The most efficient query minimizes the number of fields retrieved, uses correct relationship names, and avoids syntax errors. All options retrieve only Id fields, so efficiency depends on correct syntax and relationship names.

Analyzing the Relationship Name for Job_Application__c:

In a master-detail relationship, the child object (Job_Application__c) has a relationship field pointing to the parent (Contact). The relationship name for accessing child records from the parent is typically the plural form of the child object’s name with __r. For a custom object named Job_Application__c, the standard relationship name is Job_Applications__r. The Salesforce Apex Developer Guide explains: “For custom objects, the relationship name is usually the object name pluralized, with __r appended” (Salesforce Apex Developer Guide, Understanding Relationship Names).

However, the exact relationship name depends on the field definition. If the master-detail field on Job_Application__c was created with a custom relationship name, it could differ, but the question does not specify a custom name. Therefore, we assume the default naming convention, making Job_Applications__r the correct relationship name for the subquery.

Evaluating the Options:

A. [SELECT Id, (SELECT Id FROM Job_Applications__r) FROM Contact WHERE Accounts.Industry = 'Technology']

Subquery: Uses Job_Applications__r, which is likely the correct relationship name for Job_Application__c child records, assuming standard naming conventions.

WHERE Clause: Uses Accounts.Industry, which is incorrect. The relationship name for the Account object from Contact is Account (singular), not Accounts. The SOQL and SOSL Reference Guide states: “The relationship name for the Account object from Contact is Account” (Salesforce SOQL and SOSL Reference Guide, Relationship Queries). Using Accounts results in a SOQL syntax error: “No such field Accounts on entity Contact.”

Conclusion: Incorrect due to the invalid Accounts.Industry reference.

B. [SELECT Id, (SELECT Id FROM Job_Application__c) FROM Contact WHERE Accounts.Industry = 'Technology']

Subquery: Uses Job_Application__c, which is the object’s API name, not the relationship name. In SOQL parent-to-child queries, the subquery must use the relationship name (e.g., Job_Applications__r), not the object name. The Apex Developer Guide notes: “In a subquery, use the relationship name, not the object name” (Salesforce Apex Developer Guide, SOQL Relationship Queries). Using Job_Application__c causes a SOQL syntax error: “No such relationship Job_Application__c on Contact.”

WHERE Clause: Uses Accounts.Industry, which, as noted, is incorrect due to the invalid relationship name Accounts.

Conclusion: Incorrect due to both the invalid subquery (Job_Application__c) and the incorrect Accounts.Industry reference.

C. [SELECT Id, (SELECT Id FROM Job_Application__c) FROM Contact WHERE Account.Industry = 'Technology']

Subquery: Uses Job_Application__c, which is incorrect for the same reason as option B. The subquery must use the relationship name (Job_Applications__r), not the object name, resulting in a SOQL syntax error.

WHERE Clause: Uses Account.Industry, which is correct. The relationship name for the Account object from Contact is Account, and Industry is a valid field on Account. The Salesforce Object Reference Guide confirms: “Industry is a picklist field on the Account object” (Salesforce Object Reference Guide, Account Object).

Conclusion: Incorrect due to the invalid subquery (Job_Application__c), despite the correct Account.Industry reference.

D. [SELECT Id, (SELECT Id FROM Job_Applications__r) FROM Contact WHERE Account.Industry = 'Technology']

Subquery: Uses Job_Applications__r, which is the correct relationship name for accessing Job_Application__c child records from the Contact parent, assuming standard naming conventions.

WHERE Clause: Uses Account.Industry, which is correct, as it properly references the Account object’s Industry field via the Account relationship.

Conclusion: Correct, as it uses the proper relationship name for the subquery and the correct syntax for filtering on the Account’s Industry field.

Why Option D is Correct:

Option D is the most efficient and syntactically correct because:

It uses the correct relationship name (Job_Applications__r) for the parent-to-child subquery, adhering to Salesforce’s naming conventions for master-detail relationships.

It correctly references the Account’s Industry field using Account.Industry, aligning with the standard lookup relationship between Contact and Account.

It retrieves only the necessary fields (Id for Contact and Id for Job_Application__c), ensuring efficiency.

It satisfies the requirement to retrieve Contact records where the Account’s Industry is 'Technology' and includes related Job_Application__c records.

Potential Typos or Ambiguities:

The question is clear, with no obvious typos. However, the relationship name Job_Applications__r assumes the default pluralized naming convention. If the master-detail field on Job_Application__c was created with a custom relationship name (e.g., Applications__r), the correct answer could differ. Since the question does not specify a custom name, we follow the standard convention (Job_Applications__r).

The field Industry on Account is a standard picklist field, and 'Technology' is a common default value, so no issues arise there.

Example for Clarity:

The SOQL query in option D would look like:

apex

Copy

List contacts = [SELECT Id, (SELECT Id FROM Job_Applications__r)

FROM Contact

WHERE Account.Industry = 'Technology'];

for (Contact c : contacts) {

System.debug('Contact: ' + c.Id);

for (Job_Application__c ja : c.Job_Applications__r) {

System.debug('Job Application: ' + ja.Id);

}

}

This query retrieves all Contacts where the related Account’s Industry is 'Technology' and includes their Job_Application__c records via the subquery. The results can be iterated to access both Contact and Job_Application__c data.