DcsvIo.D2.Handler.Repo.Abstractions 0.1.1

DcsvIo.D2.Handler.Repo.Abstractions

Vocabulary for repo-flavored handlers — what app-layer code touches when it needs to discriminate database failures (unique violation, FK violation, deadlock, concurrency conflict, connection failure, etc.). Pure abstractions: zero infrastructure dependencies. EF Core, Npgsql, and any provider knowledge live in sibling packages (DcsvIo.D2.Handler.Repo, DcsvIo.D2.Handler.Repo.Postgres).

Install

dotnet add package DcsvIo.D2.Handler.Repo.Abstractions

Public API

Emitting + discriminating DB failures

Handler code returns typed DB failures via the extension factories:

return D2Result<User>.UniqueViolation(
    messages: [TK.Auth.Errors.EMAIL_ALREADY_TAKEN],
    inputErrors: [new InputError("email", "EMAIL_ALREADY_TAKEN")]);

Caller code discriminates via the boolean discriminators:

var result = await createUser.HandleAsync(input);
if (result.IsUniqueViolation)
    return Conflict(result.Messages);
if (result.IsTransientDbFailure)
    return await retryPolicy.RetryAsync(() => createUser.HandleAsync(input));
if (result.IsConcurrencyConflict)
    return await ReloadAndMergeAsync(input);

The IsTransientDbFailure predicate is a roll-up — IsDbDeadlock || IsDbTimeout || IsDbConnectionFailure. IsConcurrencyConflict is intentionally excluded — concurrency conflicts need reload-then-merge logic, not a blind retry.

IsTransientDbFailure is a separate axis from the built-in IsTransientRetryable (IsServiceUnavailable || IsRateLimited) on D2Result in the result lib. They live in separate libs because not every consumer of D2Result deals with a database; the DB roll-up only loads when the consumer references this package. A generic retry policy that wants to catch BOTH HTTP-flavored AND DB-flavored transient failures should check the union: result.IsTransientRetryable || result.IsTransientDbFailure.

Default messages

Each factory accepts an optional messages parameter; when omitted, the generic fallback from TK.Common.Errors.* is used:

These defaults are deliberately generic ("This value is already in use"). Handlers that know the constraint identity should override the message — e.g. [TK.Auth.Errors.EMAIL_ALREADY_TAKEN] instead — and attach an InputError so the form UI can highlight the offending field.

Status code mapping

Dependencies

• DcsvIo.D2.Result — base D2Result type that the factories extend
• DcsvIo.D2.I18n — TKMessage + TK codegen entry point

Zero external NuGet packages. No EF Core, no Npgsql.

Related packages

• DcsvIo.D2.Handler.Repo — BaseRepoHandler consumes the classifier interface
• DcsvIo.D2.Handler.Repo.Postgres — PostgreSQL classifier implementation