Does `call.receive<SomeDataClass>()` parse json string?

# ktor

[aeruhxi]

Does call.receive<SomeDataClass>() parse json string?

[gildor]

Yes if you have ContentNegotiation feature enabled with some Json mapping library (Gson and Jackson implementations are available as part of ktor but you should add them to dependencies)

[aeruhxi]

install(ContentNegotiation) {
        gson {
            setDateFormat(DateFormat.LONG)
            excludeFieldsWithoutExposeAnnotation()
        }
    }

Is this enough for that?

[gildor]

yes, should be enough

[aeruhxi]

https://github.com/JetBrains/kotlinconf-app/blob/c931f5513b6dd0da02c588abc191fd7211baeca7/common/src/main/kotlin/com/jetbrains/kotlinconf/data/Favorite.kt
And the data class should have nullable fields?

[aeruhxi]

I have

data class CreatePostRequest(
        val content: String?,
        val userId: Long,
        val with: List<Long>?,
        val checkedIn: Long?,
        val foodId: Long?,
        val menuCategoryId: Long?,
        val actType: String?,
        val photos:List<String> = emptyList()
)

which isn't being deserialized

[gildor]

This is different serialization feature, not related to Gson. It’s from kotlinx.serialization

[gildor]

And Gson can map even without nullable fields, but be careful, if you don’t have default constructor, Gson just skip constructor invocation so you will lose your default values and even nullability

[gildor]

isn’t being deserialized

What does it mean?

[aeruhxi]

I am getting nulls in all fields

[aeruhxi]

CreatePostRequest(content=null, userId=0, with=null, checkedIn=null, foodId=null, menuCategoryId=null, actType=null, photos=null)

[gildor]

Don’t forget that request should have type application/json, if requests have something like text/plain ContentNegotiation doesn’t work for Gson

[gildor]

Are you sure that you request has this data?

[aeruhxi]

it does have application/json

[gildor]

Gson deserialize even empty string

[gildor]

try to read raw request and check that you have some data

[aeruhxi]

{
  "content": "ABCasdasdDFE",
  "userId": 1,
  "with": [
    2,
    3
  ],
  "checkedIn": 2,
  "menuCategoryId": 1,
  "actType": "eat"
}

[gildor]

But you don’t have @Expose annotation on your fields

[gildor]

Do you really need excludeFieldsWithoutExposeAnnotation?

[gildor]

Do you understand what this feature does?

[aeruhxi]

oh mybad

[aeruhxi]

it had to do with Expose

[aeruhxi]

yeah I understand gson ignores fields without @Expose as I configured it

[gildor]

also probably you should annotate not properties, but fields

[aeruhxi]

you mean?

[gildor]

something like:

@field:Expose
val content: String?

[aeruhxi]

what is the difference?

[gildor]

Because content is property, so in bytecode it’s actually getter, setter and private field, so you should annotate field, because Gson know nothing about kotlin properties

[gildor]

I don’t see much gain from excludeFieldsWithoutExposeAnnotation for data classes

[aeruhxi]

What should I do if I want to ignore some field then?

[gildor]

Do you want ignore data class fields during serialization?

[gildor]

you can use @Transient

[gildor]

anyway, it’s of course depends on your case

[aeruhxi]

I read somewhere to not use @Transient as it has other side effects too

[gildor]

yes, for example it also excluded from from java serialization

[aeruhxi]

Also, how do I fail the json serialization if some fields are missing. I get nulls even if that field is non-nullable. I guess it's because gson doesn't know about Kotlin's nullability

[gildor]

actually, looks like instead of @field:Expose you can use just @Expose, because this annotation only targets fields, so everything should work

[gildor]

I answered to your question in another thread, you can check
https://kotlinlang.slack.com/archives/C0922A726/p1518425275000094?thread_ts=1518423310.000347&cid=C0922A726

[aeruhxi]

oh thanks