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Tradedesk·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Tradedesk software engineer interview that centered on a recipe management system design problem. They kept layering on requirements mid-question which kept me on my toes the whole time.

Questions Asked (2)

Q1

You have a Recipe Management System with name, ingredients, and steps. How would you extend the API to support sorting recipes by different criteria like name, creation time, or number of ingredients, including sort direction?

API & IntegrationsSystem DesignTechnical Trade-offs
Author's notes

I jumped straight to adding query params like sort_by and order to the list endpoint, which felt right.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the current API design and then propose adding query parameters for sorting, such as 'sortBy' and 'sortOrder', with sensible defaults. Discuss how to implement sorting efficiently, considering database indexing and in-memory sorting, and mention trade-offs like performance and flexibility. Conclude by outlining validation, error handling, and potential future extensions.

Pro tip: Mention that you would design the sorting parameters to be extensible, so new sort criteria can be added without breaking existing clients, and highlight the importance of documenting default behavior to avoid ambiguity.

1. Clarify Requirements and Current API

Ask about the existing API structure, expected scale, and whether sorting should be done server-side or client-side. Confirm the need for multiple sort criteria and direction.

2. Design Query Parameters

Propose adding optional query parameters like 'sortBy' (e.g., name, creationTime, ingredientCount) and 'sortOrder' (asc/desc). Define default values (e.g., sortBy=creationTime, sortOrder=desc) to maintain backward compatibility.

3. Implementation Strategy

Explain how to implement sorting: for database-backed systems, use ORDER BY clauses with proper indexing; for in-memory, use comparator functions. Discuss handling of null values and case sensitivity for name sorting.

4. Validation and Error Handling

Describe validating sortBy against a whitelist of allowed fields and sortOrder against asc/desc. Return 400 Bad Request for invalid values, with clear error messages.

5. Trade-offs and Extensibility

Discuss trade-offs: server-side sorting reduces client complexity but may impact performance; indexing improves speed but adds storage overhead. Suggest designing for extensibility, e.g., using a comma-separated list for multiple sort fields.

Key Points to Mention

  • Use of query parameters (sortBy, sortOrder) with defaults for backward compatibility
  • Validation of sort fields against a whitelist to prevent injection or errors
  • Database indexing on sortable fields (e.g., name, creation_time) for performance
  • Handling of null values and case-insensitive sorting for name
  • Trade-offs between server-side and client-side sorting
  • Extensibility for future sort criteria (e.g., multiple sort fields)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

How would you introduce a User entity into the system so that recipes are owned by users, and only the owner or an authorized user can modify or delete a recipe? Walk through the data model changes and the authorization logic.

Data ModelingSystem DesignTechnical Trade-offs
Author's notes

This is where things got interesting.

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AI HintsAI Generated

Suggested Approach

Start by outlining the data model changes: introduce a User entity and add an owner_id foreign key to Recipe. Then explain the authorization logic: enforce that only the owner or users with specific roles/permissions can modify or delete a recipe, using middleware or policy checks. Finally, discuss trade-offs and edge cases like ownership transfer or admin overrides.

Pro tip: Mention the importance of auditing and logging authorization failures to detect potential security issues, and consider using a centralized authorization service to avoid scattered logic.

1. Data Model Changes

Introduce a User entity with necessary fields (id, username, etc.) and add an owner_id foreign key to the Recipe entity. Consider adding a role field to User for authorization.

2. Authorization Logic

Define rules: only the owner or an authorized user (e.g., admin) can modify/delete. Implement checks at the API layer using middleware or policy-based authorization.

3. Enforcement Points

Identify where to enforce authorization: on every write operation (update, delete) and possibly on read if needed. Ensure consistency across all endpoints.

4. Edge Cases and Trade-offs

Discuss scenarios like ownership transfer, shared recipes, admin overrides, and performance implications of authorization checks. Mention caching or denormalization if needed.

5. Testing and Monitoring

Outline how to test authorization logic (unit, integration tests) and monitor for unauthorized access attempts. Suggest logging and alerting.

Key Points to Mention

  • Foreign key relationship between Recipe and User (owner_id)
  • Role-based access control (RBAC) or attribute-based access control (ABAC) for authorized users
  • Middleware or policy enforcement at the API layer
  • Handling edge cases: ownership transfer, shared access, admin privileges
  • Database constraints and indexing for performance
  • Audit logging and monitoring for security

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.