[FIXED] How to write POJOs to get specific array inside an object from JSON using Retrofit2?

Issue

I need to do a task: paging list of news. To do it I took a sample from googlesample/architecthurecomponents/PagingWithNetworkSample and encounter with this question. Question is about code from Google sample to parse JSON file.

JSON url: https://www.reddit.com/r/androiddev/hot.json

POJO file:

@Entity(tableName = "posts",
    indices = [Index(value = ["subreddit"], unique = false)])
data class RedditPost(
    @PrimaryKey
    @SerializedName("name")
    val name: String,
    @SerializedName("title")
    val title: String,
    @SerializedName("score")
    val score: Int,
    @SerializedName("author")
    val author: String,
    @SerializedName("subreddit") // this seems mutable but fine for a demo
    @ColumnInfo(collate = ColumnInfo.NOCASE)
    val subreddit: String,
    @SerializedName("num_comments")
    val num_comments: Int,
    @SerializedName("created_utc")
    val created: Long,
    val thumbnail: String?,
    val url: String?) {
// to be consistent w/ changing backend order, we need to keep a data like this
var indexInResponse: Int = -1
}

and this is an API interface:

interface RedditApi {
@GET("/r/{subreddit}/hot.json")
fun getTop(
        @Path("subreddit") subreddit: String,
        @Query("limit") limit: Int): Call<ListingResponse>

@GET("/r/{subreddit}/hot.json")
fun getTopAfter(
        @Path("subreddit") subreddit: String,
        @Query("after") after: String,
        @Query("limit") limit: Int): Call<ListingResponse>

@GET("/r/{subreddit}/hot.json")
fun getTopBefore(
        @Path("subreddit") subreddit: String,
        @Query("before") before: String,
        @Query("limit") limit: Int): Call<ListingResponse>

class ListingResponse(val data: ListingData)

class ListingData(
        val children: List<RedditChildrenResponse>,
        val after: String?,
        val before: String?
)

data class RedditChildrenResponse(val data: RedditPost)

companion object {
    private const val BASE_URL = "https://www.reddit.com/"
    fun create(): RedditApi = create(HttpUrl.parse(BASE_URL)!!)
    fun create(httpUrl: HttpUrl): RedditApi {
        val logger = HttpLoggingInterceptor(HttpLoggingInterceptor.Logger {
            Log.d("API", it)
        })
        logger.level = HttpLoggingInterceptor.Level.BASIC

        val client = OkHttpClient.Builder()
                .addInterceptor(logger)
                .build()
        return Retrofit.Builder()
                .baseUrl(httpUrl)
                .client(client)
                .addConverterFactory(GsonConverterFactory.create())
                .build()
                .create(RedditApi::class.java)
    }
}
}

The question is: how does the API request exactly finds what we need, a children: [...], which represent a list of posts? Because a children: [...] resides inside object and in code we don't have a POJO with @Serialized("children")field. Only a pojo for items inside children: [...]. I tried to implement this approach specific to my json, but it returns a null value.

Thanks everyone for help.

Solution

You don't have to add @SerializedName annotation if the name of the field in POJO is the same as the name of the field in JSON. That's why class ListingResponse(val data: ListingData) can be mapped to

{
  "kind": "Listing",
  "data": ...
}

Answered By - Andrei Tanana

Answer Checked By - Katrina (PHPFixing Volunteer)