Querying with variables
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Querying with variables
If you’re jumping in here,
git checkout 2_1.0.0(tag 2_1.0.0, or compare 2...3)
Once we click a chapter, we see “No sections,” which is true for the Preface but not for the other chapters. We need to query for the list of sections in the selected chapter. So let’s add a query document:
app/src/main/graphql/guide/graphql/toc/Sections.graphql
query Sections($id: Int!) {
chapter(id: $id) {
sections {
number
title
}
}
}After saving the file, we rebuild to get the new SectionsQuery class generated and code completion working.
The query needs the current chapter’s id, which we have in the fragment’s chapterId argument. We can execute the query as we did before in onViewCreated(), replacing showErrorMessage("No sections") with:
app/src/main/java/guide/graphql/toc/ui/sections/SectionsFragment.kt
import androidx.lifecycle.lifecycleScope
import com.apollographql.apollo.coroutines.toDeferred
import com.apollographql.apollo.exception.ApolloException
import guide.graphql.toc.SectionsQuery
import guide.graphql.toc.data.Apollo
class SectionsFragment : Fragment() {
...
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
...
lifecycleScope.launchWhenStarted {
binding.spinner.visibility = View.VISIBLE
binding.error.visibility = View.GONE
try {
val response = Apollo.client.query(
SectionsQuery(id = args.chapterId)
).toDeferred().await()
if (response.hasErrors()) {
throw Exception("Response has errors")
}
val sections = response.data?.chapter?.sections ?: throw Exception("Data is null")
if (sections.size > 1) {
adapter.updateSections(sections)
binding.spinner.visibility = View.GONE
binding.error.visibility = View.GONE
} else {
throw Exception("No sections")
}
} catch (e: ApolloException) {
showErrorMessage("GraphQL request failed")
} catch (e: Exception) {
showErrorMessage(e.message.orEmpty())
}
}
}
}We include the variable like this: SectionsQuery(id = args.chapterId), and as before, we either show an error message or update the adapter. When the API returns a single section for a chapter, it’s actually a sectionless chapter, like the Preface.
We need to implement the adapter’s updateSections() function. For the argument type, we can use the generated SectionsQuery.Section data class:
app/src/main/java/guide/graphql/toc/ui/sections/SectionsAdapter.kt
import guide.graphql.toc.SectionsQuery
class SectionsAdapter(
private val context: Context,
private val chapterNumber: Int,
private var sections: List<SectionsQuery.Section> = listOf()
) : RecyclerView.Adapter<SectionsAdapter.ViewHolder>() {
...
fun updateSections(sections: List<SectionsQuery.Section>) {
this.sections = sections
notifyDataSetChanged()
}
override fun getItemCount(): Int {
return sections.size
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val section = sections[position]
section.let {
holder.binding.sectionTitle.text = context.getString(
R.string.section_title,
chapterNumber.toString(),
section.number.toString(),
section.title
)
}
}
}Now when we select Chapter 2, we see the list of sections 💃.
