Interview questions in Backend Dev, page 3
How FastAPI uses type hints for validation
Hints drive parsing, validation, and conversion; a path declared int is coerced or returns 422; OpenAPI is auto-generated.
Circular dependencies in CommonJS modules
When A requires B which requires A, the cache returns A's partial exports; fields defined later are undefined at that moment.
Normalizing a flat orders table to 3NF
Split repeating data, remove partial dependencies, remove transitive dependencies, define keys.
Default integer overflow behavior in Go versus Rust
Go wraps silently; Rust panics in debug, wraps in release; Rust has wrapping_, checked_, saturating_ methods; Go needs manual checks.
Diamond dependencies and nested node_modules
Npm hoists one version to the top and nests the conflicting version under the dependent package; both coexist on disk.
Modeling one-to-many versus many-to-many relationships
One-to-many uses a foreign key on the many side; many-to-many needs a junction table with two foreign keys.
What is the difference between a path parameter and a query parameter?
Tests REST API design and FastAPI binding. A strong answer states path params identify resources in the URL while query params filter after the question mark, then codes user_id in the route and q: str | None = None in the function.
Go nil pointers vs Rust Option: impact on signatures and safety
Tests encoding of absence. Go nil means any pointer may be null, pushing checks to runtime; Rust Option<T> forces compile-time handling. Strong answers cover signatures, validity, and NPO. Red flag: calling Option syntactic sugar for null.
Monorepo workspaces vs private npm packages
Workspaces give atomic cross-service changes and instant local linking but couple release cadence; private packages give versioned isolation but add publish overhead and version drift.
Adjacency List versus Nested Set for hierarchies
Adjacency list is simple writes but recursive reads; nested set is fast subtree reads but costly writes.
How does FastAPI distinguish required optional and default query parameters
Tests whether you know FastAPI infers query parameter optionality from Python signature defaults. Answer: no default means required, Optional[T] = None means optional, T = value sets a default, with all three in one signature.
Shadowing in Go and Rust: idioms, bugs, and if-block scoping
Tests lexical scoping in Go and Rust. Strong answers show Go's := narrowing and Rust's let rebinding, warn that Go's if := scopes across both branches, and contrast that with Rust's block-local let. Red flag: calling shadowing mutation.
The three states of a JavaScript Promise
Pending, fulfilled, rejected; settle is one-way and final; create with the executor calling resolve or reject, consume with then and catch.
3NF versus BCNF and the overlapping-key gap
BCNF requires every determinant be a superkey; 3NF allows exceptions for prime attributes.
What standard and code elements power FastAPI's auto-generated API docs?
Tests whether you know FastAPI uses the OpenAPI standard and extracts metadata from Python type hints, Pydantic models, decorators, and docstrings to build interactive docs. Red flag: claiming you must manually maintain a separate schema file.
How do you append to a Go slice and why reassign?
Tests slice headers and append reallocation. A strong answer reassigns the result (s = append(s, 4)), explains that append may allocate a new backing array, and warns that ignoring the return value drops elements. Red flag: calling append without assignment.
Output order of sync, microtask, and macrotask
C runs first synchronously, then B drains from the microtask queue, then A from the macrotask queue.
Polymorphic associations and referential integrity
A single column can't FK two tables, so integrity is unenforced; alternatives use exclusive arcs or per-type tables.
FastAPI non-integer query param default behavior
Tests FastAPI's automatic Pydantic validation and default error contracts. Strong answer: 422 Unprocessable Entity with JSON detail array containing loc, msg, and type fields. Red flag: saying 400 Bad Request or manual validation is needed.
Define a WebEvent enum with PageLoad, PageUnload, and KeyPress
Tests Rust enum syntax: unit versus tuple variants. A good answer defines WebEvent with PageLoad, PageUnload, and KeyPress(char), then instantiates WebEvent::KeyPress('q'). A red flag is forgetting the double colon or using struct variant syntax.
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