android retrofit post request - exclude field from the body

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Basically, @Expose will not be regarded by the default Gson instance. In order to utilize it, you'll need to use a custom Gson instance:

GsonBuilder builder = new GsonBuilder();  
builder.excludeFieldsWithoutExposeAnnotation();  
Gson gson = builder.create();  

but if you do this you'll have to add @Expose to every field in all your model classes or they won't be serialised or deserialised by GSON.

I assume you're using Gson. You can use transient.

private transient int id;

If you require a more complicated solution, take a look at Gson: How to exclude specific fields from Serialization without annotations

This is how to do it with Retrofit

    val gson: Gson = GsonBuilder().excludeFieldsWithoutExposeAnnotation().create()

    builder = Retrofit.Builder()
            .client(okHttpClient)
            .baseUrl(URL)
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())

And in your model

// These values are read as JSON objects only in server response
@SerializedName("someField")
@Expose(serialize = false, deserialize = true)
var someField: String? = null

For example here, we will not send JSON object to server (deserialize = false) but we will receive it as response (deserialize = true)