API Endpoint Creator Skill

Creates complete RPC-style API endpoints following strict layered architecture patterns.

When to Use

• Creating a new REST API endpoint from scratch
• Adding CRUD operations for a new domain entity
• Setting up the full stack: Controller → Manager → Repository → Tests
• Need a Retrofit client for integration testing

Process

1. Create Response/Request Models

Location: app/module-client/src/main/kotlin/com/yourcompany/client/response/{domain}/

package com.yourcompany.client.response.{domain}

import com.yourcompany.postgresql.entity.{Domain}Entity
import java.time.Instant
import java.util.UUID

data class {Domain}Response(
  val id: UUID,
  val name: String,
  val status: String,
  val createdAt: Instant,
  val updatedAt: Instant?
) {
  companion object {
    fun from(entity: {Domain}Entity): {Domain}Response = {Domain}Response(
      id = entity.id,
      name = entity.name,
      status = entity.status,
      createdAt = entity.createdAt,
      updatedAt = entity.updatedAt
    )
  }
}

data class {Domain}ListResponse(
  val items: List<{Domain}Response>,
  val total: Int,
  val page: Int,
  val limit: Int,
  val hasMore: Boolean
)

Location: app/module-client/src/main/kotlin/com/yourcompany/client/request/{domain}/

package com.yourcompany.client.request.{domain}

data class Create{Domain}Request(
  val name: String,
  val description: String? = null
)

data class Update{Domain}Request(
  val name: String? = null,
  val description: String? = null,
  val status: String? = null
)

Key: All models in module-client, never in controllers or managers.

2. Create Controller

Location: app/api-application/src/main/kotlin/com/yourcompany/controller/{Domain}Controller.kt

package com.yourcompany.controller

import com.yourcompany.{domain}.contract.{Domain}Manager
import com.yourcompany.client.request.{domain}.Create{Domain}Request
import com.yourcompany.client.request.{domain}.Update{Domain}Request
import com.yourcompany.client.response.{domain}.{Domain}Response
import com.yourcompany.client.response.{domain}.{Domain}ListResponse
import com.yourcompany.exception.throwOrValue
import io.micronaut.http.annotation.*
import io.micronaut.scheduling.TaskExecutors
import io.micronaut.scheduling.annotation.ExecuteOn
import io.micronaut.security.annotation.Secured
import io.micronaut.validation.Validated
import io.swagger.v3.oas.annotations.tags.Tag
import jakarta.validation.Valid
import java.util.UUID

@ExecuteOn(TaskExecutors.IO)
@Validated
@Controller("/api/v1/{domain}")
@Tag(name = "{Domain}", description = "{Domain} API")
@Secured(SecurityRule.IS_AUTHENTICATED)
class {Domain}Controller(
  private val {domain}Manager: {Domain}Manager
) {

  @Get("/{domain}s")
  suspend fun list(
    @QueryValue page: Int?,
    @QueryValue limit: Int?,
    @QueryValue status: String?
  ): {Domain}ListResponse {
    return {domain}Manager.list(
      page = page ?: 1,
      limit = limit ?: 20,
      status = status
    ).throwOrValue()
  }

  @Get("/{domain}")
  suspend fun getById(
    @QueryValue id: UUID
  ): {Domain}Response {
    return {domain}Manager.byId(id).throwOrValue()
  }

  @Post("/{domain}")
  suspend fun create(
    @Valid @Body request: Create{Domain}Request
  ): {Domain}Response {
    return {domain}Manager.create(request).throwOrValue()
  }

  @Post("/{domain}/update")
  suspend fun update(
    @QueryValue id: UUID,
    @Valid @Body request: Update{Domain}Request
  ): {Domain}Response {
    return {domain}Manager.update(id, request).throwOrValue()
  }

  @Post("/{domain}/delete")
  suspend fun delete(
    @QueryValue id: UUID
  ): Boolean {
    return {domain}Manager.deleteById(id).throwOrValue()
  }
}

Key Points:

• @ExecuteOn(TaskExecutors.IO) required for suspend functions
• Query params for ALL identifiers (@QueryValue id: UUID)
• Thin methods - just delegate to manager
• .throwOrValue() to unwrap Either
• Inject Manager only (never Repository)
• NO inline data classes

3. Create Manager Interface

Location: app/module-{domain}/module-api/src/main/kotlin/com/yourcompany/{domain}/contract/{Domain}Manager.kt

package com.yourcompany.{domain}.contract

import arrow.core.Either
import com.yourcompany.client.request.{domain}.Create{Domain}Request
import com.yourcompany.client.request.{domain}.Update{Domain}Request
import com.yourcompany.client.response.{domain}.{Domain}Response
import com.yourcompany.client.response.{domain}.{Domain}ListResponse
import com.yourcompany.exception.ClientException
import java.util.UUID

interface {Domain}Manager {
  suspend fun list(
    page: Int,
    limit: Int,
    status: String?
  ): Either<ClientException, {Domain}ListResponse>

  suspend fun byId(id: UUID): Either<ClientException, {Domain}Response>

  suspend fun create(
    request: Create{Domain}Request
  ): Either<ClientException, {Domain}Response>

  suspend fun update(
    id: UUID,
    request: Update{Domain}Request
  ): Either<ClientException, {Domain}Response>

  suspend fun deleteById(id: UUID): Either<ClientException, Boolean>
}

4. Create Manager Implementation

Location: app/module-{domain}/module-impl/src/main/kotlin/com/yourcompany/{domain}/impl/Default{Domain}Manager.kt

package com.yourcompany.{domain}.impl

import arrow.core.Either
import arrow.core.left
import arrow.core.right
import com.yourcompany.database.DatabaseContext
import com.yourcompany.{domain}.contract.{Domain}Manager
import com.yourcompany.client.request.{domain}.Create{Domain}Request
import com.yourcompany.client.request.{domain}.Update{Domain}Request
import com.yourcompany.client.response.{domain}.{Domain}Response
import com.yourcompany.client.response.{domain}.{Domain}ListResponse
import com.yourcompany.exception.ClientError
import com.yourcompany.exception.ClientException
import com.yourcompany.postgresql.entity.{Domain}Entity
import com.yourcompany.postgresql.repository.{Domain}Repository
import org.jetbrains.exposed.sql.transactions.transaction
import java.util.UUID

class Default{Domain}Manager(
  private val {domain}Repository: {Domain}Repository,
  private val db: DatabaseContext
) : {Domain}Manager {

  override suspend fun byId(id: UUID): Either<ClientException, {Domain}Response> {
    val entity = {domain}Repository.byId(id)
      ?: return ClientError.{DOMAIN}_NOT_FOUND.asException().left()

    return {Domain}Response.from(entity).right()
  }

  override suspend fun create(
    request: Create{Domain}Request
  ): Either<ClientException, {Domain}Response> {
    val entity = {Domain}Entity(
      name = request.name,
      description = request.description
    )

    val inserted = transaction(db.primary) {
      {domain}Repository.insert(entity)
    }

    return {Domain}Response.from(inserted).right()
  }

  override suspend fun update(
    id: UUID,
    request: Update{Domain}Request
  ): Either<ClientException, {Domain}Response> {
    val existing = {domain}Repository.byId(id)
      ?: return ClientError.{DOMAIN}_NOT_FOUND.asException().left()

    val updated = transaction(db.primary) {
      {domain}Repository.update(
        id = id,
        name = request.name,
        description = request.description,
        status = request.status
      )
    } ?: return ClientError.{DOMAIN}_NOT_FOUND.asException().left()

    return {Domain}Response.from(updated).right()
  }

  override suspend fun deleteById(id: UUID): Either<ClientException, Boolean> {
    val deleted = transaction(db.primary) {
      {domain}Repository.deleteById(id)
    }

    return if (deleted != null) {
      true.right()
    } else {
      ClientError.{DOMAIN}_NOT_FOUND.asException().left()
    }
  }
}

Key Points:

• Use {Domain}Response.from(entity) for conversions (companion object pattern)
• transaction(db.primary) for writes
• Return Either.left() for errors, Either.right() for success
• NO !! operators

5. Register Factory Bean

Location: app/module-{domain}/module-impl/src/main/kotlin/com/yourcompany/runtime/factory/{Domain}ManagerFactory.kt

package com.yourcompany.runtime.factory

import com.yourcompany.database.DatabaseContext
import com.yourcompany.{domain}.impl.Default{Domain}Manager
import com.yourcompany.{domain}.contract.{Domain}Manager
import com.yourcompany.postgresql.repository.{Domain}Repository
import io.micronaut.context.annotation.Factory
import jakarta.inject.Singleton

@Factory
class {Domain}ManagerFactory {

  @Singleton
  fun provide{Domain}Manager(
    {domain}Repository: {Domain}Repository,
    db: DatabaseContext
  ): {Domain}Manager {
    return Default{Domain}Manager({domain}Repository, db)
  }
}

6. Create Retrofit Client

Location: app/module-client/src/main/kotlin/com/yourcompany/client/{Domain}Client.kt

package com.yourcompany.client

import com.yourcompany.client.request.{domain}.Create{Domain}Request
import com.yourcompany.client.request.{domain}.Update{Domain}Request
import com.yourcompany.client.response.{domain}.{Domain}Response
import com.yourcompany.client.response.{domain}.{Domain}ListResponse
import retrofit2.http.*
import java.util.UUID

interface {Domain}Client {

  @GET("/api/v1/{domain}s")
  suspend fun list(
    @Header("Authorization") authorization: String,
    @Query("page") page: Int? = null,
    @Query("limit") limit: Int? = null,
    @Query("status") status: String? = null
  ): {Domain}ListResponse

  @GET("/api/v1/{domain}")
  suspend fun getById(
    @Header("Authorization") authorization: String,
    @Query("id") id: UUID
  ): {Domain}Response

  @POST("/api/v1/{domain}")
  suspend fun create(
    @Header("Authorization") authorization: String,
    @Body request: Create{Domain}Request
  ): {Domain}Response

  @POST("/api/v1/{domain}/update")
  suspend fun update(
    @Header("Authorization") authorization: String,
    @Query("id") id: UUID,
    @Body request: Update{Domain}Request
  ): {Domain}Response

  @POST("/api/v1/{domain}/delete")
  suspend fun delete(
    @Header("Authorization") authorization: String,
    @Query("id") id: UUID
  ): Boolean
}

7. Create Integration Test

Location: app/api-application/src/test/kotlin/com/yourcompany/{Domain}ControllerTest.kt

See testing-patterns.md for complete test examples.

8. Run Tests

./gradlew :app:api-application:test --tests "{Domain}ControllerTest"
./gradlew test

Interaction Style

• Always generates the full stack: models, controller, manager, factory, client, tests
• Follows the project's exact patterns — no shortcuts or creative alternatives
• Uses query parameters for all IDs, never path parameters
• Asks which domain entity before starting if not clear from context

Rules

RPC-Style API (POST for Mutations, Query Params Only)

This project uses RPC-style endpoints: @Get for reads, @Post for all mutations, query parameters for all IDs:

GET  /api/v1/employees              # List employees (plural)
GET  /api/v1/employee               # Get one employee (?id=xxx)
POST /api/v1/employee               # Create employee
POST /api/v1/employee/update        # Update employee
POST /api/v1/employee/delete        # Delete employee (soft)

Rules from API_RULES.md:

• NEVER use path parameters (/{id})
• Use query parameters: @QueryValue id: UUID
• Singular nouns for single resource, plural for collections
• Use verb sub-paths for actions (/delete, /restore)

Layered Architecture

HTTP Request → Controller → Manager → Repository → Database

Controller: Thin (just delegation), HTTP annotations, @ExecuteOn(TaskExecutors.IO), @Secured, unwrap Either with .throwOrValue()

Manager: All business logic, returns Either<ClientException, T>, wraps DB operations in transactions, never throws exceptions

Repository: Data access only (already exists)

NO !! Operator

val employee = employeeRepository.byId(id)
  ?: return ClientError.EMPLOYEE_NOT_FOUND.asException().left()

Error Handling Patterns

Not Found

val entity = repository.byId(id)
  ?: return ClientError.{DOMAIN}_NOT_FOUND.asException().left()

Already Exists

val existing = repository.byEmail(email)
if (existing != null) {
  return ClientError.EMAIL_ALREADY_IN_USE.asException().left()
}

Output

• Controller is thin (just delegation)
• Controller has @ExecuteOn(TaskExecutors.IO)
• NO path parameters (use @QueryValue for all IDs)
• Manager returns Either (never throws)
• Transactions wrap DB operations
• No !! operator
• Response models in module-client with companion object { fun from() }
• NO inline data classes in controllers
• Integration tests use Retrofit client
• All tests pass