add customer controller with find by guid method

src/main/kotlin/com/example/demo/http/controllers/CustomerController.kt

@@ -0,0 +1,30 @@
+package com.example.demo.http.controllers
+
+import com.example.demo.http.exceptions.NotFoundException
+import com.example.demo.services.database.customer.CustomerService
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.http.HttpStatus
+import org.springframework.http.MediaType
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PathVariable
+import org.springframework.web.bind.annotation.RequestMapping
+import org.springframework.web.bind.annotation.RestController
+import java.util.*
+
+@RestController
+@RequestMapping(value = ["/api/customer"], produces = [MediaType.APPLICATION_JSON_VALUE])
+class CustomerController(
+    @Autowired
+    private val customerService: CustomerService,
+) {
+    @GetMapping("/{guid}")
+    @Throws(NotFoundException::class)
+    fun getCustomer(
+        @PathVariable guid: UUID,
+    ): ResponseEntity<Any> {
+        val customer = customerService.findByGuid(guid) ?: throw NotFoundException()
+
+        return ResponseEntity(customer, HttpStatus.OK)
+    }
+}

src/main/kotlin/com/example/demo/models/Customer.kt

@@ -10,6 +10,7 @@ import java.time.OffsetDateTime
 import java.util.*
 
 @Table("customer")
+@Serializable
 data class Customer(
     @Id
     val id: Long?,

src/main/kotlin/com/example/demo/models/CustomerExtended.kt

@@ -0,0 +1,9 @@
+package com.example.demo.models
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class CustomerExtended(
+    val customer: Customer,
+    val city: City?,
+)

src/main/kotlin/com/example/demo/services/database/customer/CustomerService.kt

@@ -1,11 +1,12 @@
 package com.example.demo.services.database.customer
 
 import com.example.demo.models.Customer
+import com.example.demo.models.CustomerExtended
 import com.example.demo.services.database.exceptions.CityNotFoundException
 import java.util.*
 
 interface CustomerService {
-    fun findByGuid(guid: UUID): Customer?
+    fun findByGuid(guid: UUID): CustomerExtended?
 
     @Throws(CityNotFoundException::class)
     fun create(name: String, cityGuid: UUID?): Customer

src/main/kotlin/com/example/demo/services/database/customer/CustomerServiceImpl.kt

@@ -1,6 +1,7 @@
 package com.example.demo.services.database.customer
 
 import com.example.demo.models.Customer
+import com.example.demo.models.CustomerExtended
 import com.example.demo.providers.CityRepository
 import com.example.demo.providers.CustomerRepository
 import com.example.demo.services.database.exceptions.CityNotFoundException
@@ -11,7 +12,17 @@ class CustomerServiceImpl(
     private val customerRepository: CustomerRepository,
     private val cityRepository: CityRepository
 ): CustomerService {
-    override fun findByGuid(guid: UUID): Customer? = customerRepository.findByGuid(guid)
+    override fun findByGuid(guid: UUID): CustomerExtended? {
+        val customer = customerRepository.findByGuid(guid) ?: return null
+
+        if (customer.cityId == null) {
+            return CustomerExtended(customer, null)
+        }
+
+        val city = cityRepository.findById(customer.cityId)
+
+        return CustomerExtended(customer, city.orElse(null))
+    }
 
     override fun create(name: String, cityGuid: UUID?): Customer {
         val cityId: Long? = cityGuid?.let {