feat: generate Create/Update DTO classes as mapped-type compositions (makeDtoFiles)

[kimjbstar]

Closes the last real item on the README's "Future Plan".

Why now — the stated philosophy had already been overtaken

Per-model Create/Update DTOs were deferred on the grounds that deciding what a create payload looks like belongs to the developer. That reasoning no longer matches what this generator does:

• useValidation decides which validators are right for a field
• useSerialization + /// @exclude decide what leaves a response
• validateNestedRelations assumes a nested payload shape
• a literal @default(...) already becomes a Swagger example

DTOs were the one place the old statement was still being applied. Applying the repo's actual rule produces this feature rather than blocking it.

That rule is "reflect what the schema states, never guess from a field's name" — the #34/#56/#76 Date misdetection being the cautionary tale. Which fields a client can't supply on create is stated outright in the schema, so nothing here is inferred:

field	schema fact	in Create?
id Int @id @default(autoincrement())	function default	omitted
createdAt DateTime @default(now())	function default	omitted
computed String @default(dbgenerated(...))	function default	omitted
updatedAt DateTime @updatedAt	isUpdatedAt	omitted
author Author @relation(...)	relation	omitted
authorId String	FK scalar	kept — what a REST client actually posts
views Int @default(0)	literal default	kept — "there's a fallback" ≠ "you may not set it"
id String @id (no default)	no default	kept — the caller has to provide it

DMMF represents function defaults as an { name, args } object, which is exactly what distinguishes them from literal ones — verified against real DMMF, not assumed.

What it generates

Compositions, not copies:

// create_post.ts
import { Post } from './post'
import { OmitType } from '@nestjs/swagger'
export class CreatePost extends OmitType(Post, ['id', 'createdAt', 'updatedAt', 'author'] as const) {}

// update_post.ts
import { CreatePost } from './create_post'
import { PartialType } from '@nestjs/swagger'
export class UpdatePost extends PartialType(CreatePost) {}

A field's type, Swagger metadata and validators stay declared in exactly one place. This is deliberately a different shape from prisma-generator-nestjs-dto's fully expanded per-DTO classes — and it's the same composition the README FAQ has always told people to write by hand. Mapped types come from @nestjs/swagger when useSwagger is on, @nestjs/mapped-types otherwise.

Verified end to end, not just as strings

Generated output (models + DTOs + enums + nullable fields + useNonNullableAssertions) compiled against a real @nestjs/swagger install:

$ tsc --noEmit --strict
(no output — 0 errors)

And at runtime, the mapped types really do carry the decorators through:

1) Create에 id/createdAt/updatedAt/author 키 없음 : OK
2) Create 잘못된 값 → title(isString) views(isInt) authorId(isString) status(isEnum)
3) Create 올바른 값 → 에러 없음
4) Update {} → 에러 없음 (partial)
5) Update {title:123} → title(isString)

That exercise is also what turned up the TS1263 bug fixed separately in #106.

Implementation notes

• ClassComponent gains extendsExpression/generatedClassImports/externalImports; with extendsExpression set it renders from a new DTO_CLASS_TEMPLATE with no body of its own.
• The base-class import goes through FileComponent.TEMP_PREFIX like relation imports, so it resolves to the real snake_case path once every file's location is known. Unlike a relation field it must be a value import — the name appears in an extends clause, which a type-only import can't serve.
• Omitted keys are read off the generated base class's fields, not off the model, so separateRelationFields (whose base has already dropped relations) and /// @skip can't produce an OmitType key that isn't keyof the class. There's a test for exactly that.
• GraphQL helper imports are skipped for DTO files — with no fields they'd be guaranteed-unused.
• Composite types (MongoDB type blocks) get no DTOs: embedded values, not entities with endpoints.

Compatibility

Off by default. Fixture snapshots are unchanged, so existing output is byte-identical. 228 tests pass (13 new). README options/FAQ/comparison table and the "Future Plan" list are updated.

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