Drills

.NETASP.NET CoreC#EF CoreSQL Server

Enforce If-Match with rowversion

Maps an HTTP ETag precondition to EF Core rowversion and returns 412 when the representation is stale.

Expire sessions with ExecuteUpdateAsync

Performs a set-based bulk update without loading session entities into the change tracker.

Filter orders by line item without duplicate orders

Uses EXISTS instead of a row-multiplying join when the related table is only a filter.

Find duplicate normalized email addresses

Groups normalized email values to identify duplicates before adding or repairing a uniqueness rule.

Find each user's longest login streak

Uses the gaps-and-islands pattern to find consecutive login-day streaks after deduplicating same-day activity.

Find products matching every selected tag

Solves a many-to-many all-match filter with grouping and a deliberate empty-selection rule.

Find the first non-repeating character

Implements a stable first-unique-character search using counts and original order.

Find users who have never placed an order

Uses NOT EXISTS to express an anti-join without null traps or duplicate parent rows.

Fix a time-based hydration mismatch

Moves non-deterministic browser-only rendering behind a stable server snapshot and post-hydration update.

Next.jsReactTypeScript

Flatten a category tree to paths

Flattens a tree into display paths while preserving order and preventing simple cycles.

Flatten a category tree with a recursive CTE

Uses a recursive CTE to return hierarchy depth and a readable root-to-node path.

Group orders by customer summary

Builds customer summaries from order rows using grouping, aggregation, and deterministic ordering.

.NETASP.NET CoreC#EF CoreSQL+1

Guard an endpoint against N plus one queries

Uses a test-only DbCommandInterceptor to fail a regression when database command count grows with page size.

.NETASP.NET CoreC#EF CoreSQL+1

Handle a rowversion conflict in an update endpoint

Uses the client's original rowversion to detect a lost update and return a deliberate conflict response.

Handle downstream timeout and cancellation

Separates caller cancellation from a dependency timeout and maps expected downstream outcomes safely.

.NETASP.NET CoreC#

Implement a bounded PDF upload endpoint

Validates size and signature, writes under a generated storage key, and keeps untrusted files outside the public web root.

.NETASP.NET CoreC#

Implement an atomic bulk status update

Validates a bounded command set completely before applying all updates in one SaveChanges transaction.

Implement and test a production-safe readiness check

Builds a bounded readiness check for one required dependency while keeping liveness independent and responses non-sensitive.

.NETASP.NET CoreC#xUnit

Implement an optimistic favorite with rollback

Applies an immediate reversible mutation, blocks overlapping writes, and restores the previous state on failure.

Next.jsReactTypeScript

Implement a persisted idempotent POST

Stores an idempotency key, request hash, and response in the same transaction as the created resource.

Implement a simple fixed-window rate limiter

Implements a small in-memory fixed-window rate limiter with per-key counters.

Implement a simple LRU cache

Implements a small LRU cache using a dictionary plus linked list for O(1) get and put.

Implement a stable EF Core keyset page

Implements descending keyset pagination in LINQ using a compound timestamp-and-id cursor.

Import records in bounded EF Core batches

Processes a large import in chunks with fresh DbContexts, idempotent keys, cancellation, and bounded tracker growth.