Getting JSON parse error on JSON property createdAt when not included in request body - spring-boot

Question

I am recently learning to build REST APIs with Kotlin and Spring Boot. I was trying to create my first domain model and controller end-point. Here is the implementation of the Country model and CountryController countroller.
/model/Country.kt
package com.example.example.model
import jakarta.persistence.Column
import jakarta.persistence.Entity
import jakarta.persistence.EntityListeners
import jakarta.persistence.GeneratedValue
import jakarta.persistence.GenerationType
import jakarta.persistence.Id
import jakarta.persistence.Table
import org.springframework.data.annotation.CreatedDate
import org.springframework.data.annotation.LastModifiedDate
import org.springframework.data.jpa.domain.support.AuditingEntityListener
import java.sql.Timestamp
#Entity
#Table(name = "country")
class Country (
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "country_id")
val id: Int,
val code: String,
val displayName: String,
#CreatedDate
#Column(name = "created_at", nullable = false, updatable = false)
val createdAt: Timestamp,
#LastModifiedDate
#Column(name = "updated_at", nullable = false)
val updatedAt: Timestamp
)
/controller/CountryCountroller.kt
package com.example.example.controller
import com.example.example.model.Country
import com.example.example.repository.CountryRepository
import jakarta.validation.Valid
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.web.bind.annotation.RequestBody
import org.springframework.web.bind.annotation.RestController
import org.springframework.http.MediaType
import org.springframework.web.bind.annotation.PostMapping
#RestController
class CountryController {
#Autowired
lateinit var countryRepository: CountryRepository
#PostMapping("/countries", consumes = arrayOf(MediaType.APPLICATION_JSON_VALUE))
fun createCountry(#Valid #RequestBody country: Country): Country {
return countryRepository.save(country);
}
}
Schema of the Country table:
country_id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
code VARCHAR(3) NOT NULL,
displayName VARCHAR(40) NOT NULL,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (country_id)
When I started running the Spring Boot application and use Postman to call the POST /countries API, I received a 400 Bad Request error. The application error log says:
2023-01-12T14:09:15.423Z WARN 90037 --- [nio-8080-exec-3] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Instantiation of [simple type, class com.example.example.model.Country] value failed for JSON property createdAt due to missing (therefore NULL) value for creator parameter createdAt which is a non-nullable type]
The request body is a json and the request header has include the correct Content-Type information:
{
"code": "FRA",
"displayName": "France"
}
I suspected that the Spring Boot did not ignore the two fields createdAt and updatedAt, therefore I have tried to add #JsonIgnore above createdAt and updatedAt. Unfortunately the same 400 Bad Request error was still returned.
Do I actually have to include createdAt and updatedAt in the JSON request body? However, what I wanted to achieve is that the createdAt and updatedAt should be added/updated either by the Spring Boot application putting the createdAt and updatedAt data when calling the repository methods or by MySQL DB when the query is being run. Is there any way to do so?

Answer 1

You are mixing up two concepts here
whether on not createdAt and updatedAt are allowed be null in your data model
serialization:
whether you want the RestController to deserialize the fields when you receive them in the POST
whether you want the RestController to serialize the fields when you implement a GET request
By using #JsonIgnore (or the Kotlin variation #set:JsonIgnore you are just avoiding the data deserialization but still the data model requires a value. The JPA annotations are going to get executed when you put the data in the database, but in the time that the object is created by the MVC infrastructure, and before the database save happens, the data does not match the model contract.
There are two solutions to what you want to do:
Relax the data model
Change your data model to allow nulls in the two fields:
#CreatedDate
#Column(name = "created_at", nullable = false, updatable = false)
val createdAt: Timestamp?,
#LastModifiedDate
#Column(name = "updated_at", nullable = false)
val updatedAt: Timestamp?
BTW I would expect you to get the error on id as well, perhaps an Exception would be given for that once you dealt with the two dates, because again, your POST data does not supply id and this not nullable.
Use a Request object
Create a simpler data model that is used to receive your POSTed data and then create the Domain/Database model object from it.
I use a mix of the two techniques depending on circumstances. The latter approach has benefit, e.g. when you have large objects which may only be partially sent by the client (think PATCH).