how pass query variables to client in every request ?

[namdroid]

Question

my request shows like that:

curl --request POST \
 -H 'Content-Type: application/json' \
 --data '{"query":"query GetBestSellers($category: ProductCategory){bestSellers(category: $category){title}}", "operationName":"GetBestSellers", "variables":{"category":"BOOKS"}}' \
 https://rover.apollo.dev/quickstart/products/graphql

How can i pass "variables":{"category":"BOOKS"}} ?

[martinbonnin]

Hi 👋 Apollo Kotlin uses codegen to generate models for your operation. In this example, you should get a GetBestSellers(category: ProductCategory) class where you can pass your variables. You can take a look at https://www.apollographql.com/docs/kotlin/advanced/operation-variables for more details.

[namdroid]

Hi Martin, of course i can pass parameter to GetBestSellers directly, but waht i need is a addtional variables

{"query":"query
{
  footer(lang: GERMAN) {
      links {
        text
        url
      }
    }
  }
}", "variables":{"appName":"myapp"}}'

[namdroid]

in javascript should be:

const gqlResp = await client
      .query({
        query,
        variables: {
          lang,
          appName: 'myApp',
          ...moreVariables,
        },
        fetchPolicy: 'no-cache',
      });

[martinbonnin]

Looking at your initial query:

query GetBestSellers($category: ProductCategory){
  bestSellers(category: $category) {
    title
  }
}

This query defines a $category variable, which is sent as JSON and Apollo Kotlin will serialize it automatically when you construct a GetBestSellers operation:

val operation = GetBestSellers(ProductCategory(Books))

Your second query doesn't have an appName variable:

query {
  footer(lang: GERMAN) {
    links {
      text
      url
    }
  }
}

You could patch the HTTP POST body to include additional variables if that's what you're trying to do but I would recommend against that. variables is for GraphQL variables. It's surprising to pass values there that are not in your GraphQL operation.

If you're trying to send additional context to your server, I would recommend using an HTTP header instead.

[namdroid]

Ho can i patch the HTTP POST body to include additional variables ?

[martinbonnin]

The most efficient way is to implement your own HttpRequestComposer.

Another easier albeit slightly less efficient (because it needs to rewrite the post body), is to use OkHttp interceptors

[namdroid]

thanks martin, so here is my HttpRequestComposer class:

    class GraphQLHttpRequestComposer(url: String, gson: Gson) : HttpRequestComposer {
        override fun <D : Operation.Data> compose(apolloRequest: ApolloRequest<D>): HttpRequest {
            val operation = apolloRequest.operation

            // Create a MapJsonWriter to capture variables
            val mapJsonWriter = MapJsonWriter()

            // Convert the captured map to a JsonObject
            val variablesJson = gson.toJsonTree(mapJsonWriter.root()).asJsonObject

            // Add appName to variables
            variablesJson.addProperty("appName", „MyApp“)

            // Create the full request body
            val bodyJson = JsonObject().apply {
                addProperty("query", operation.document())
                addProperty("operationName", operation.name())
                add("variables", variablesJson)
            }

            val bodyString = gson.toJson(bodyJson)

            val httpBody = object : HttpBody {
                override val contentLength: Long = bodyString.toByteArray().size.toLong()
                override val contentType: String = "application/json; charset=utf-8"

                override fun writeTo(bufferedSink: BufferedSink) {
                    bufferedSink.writeUtf8(bodyString)
                }
            }

            return HttpRequest.Builder(HttpMethod.Post, "url")
                .addHeader("Content-Type", "application/json")
                .body(httpBody)
                .build()
        }
    }

    fun provideApolloClient(okHttpClient: OkHttpClient, graphqlUrl: String): ApolloClient {

        val networkTransport = HttpNetworkTransport.Builder()
            .httpRequestComposer(GraphQLHttpRequestComposer(graphqlUrl, gson))
            .okHttpClient(okHttpClient)
            .build()

        return ApolloClient.Builder()
            .networkTransport(networkTransport)
            .addInterceptor(LoggingApolloInterceptor())
            .httpMethod(HttpMethod.Get)
            .autoPersistedQueries()
            .build()
    }

But it don't work !I don't know why

[namdroid]

may new method added to Apollo client in the future that support variables in request body ?

[martinbonnin]

Try something like below (wildly untested):

class MyHttpRequestComposer(val serverUrl: String): HttpRequestComposer {
  override fun <D : Operation.Data> compose(apolloRequest: ApolloRequest<D>): HttpRequest {
    check(apolloRequest.httpMethod == HttpMethod.Post) {
      "This composer only supports POST"
    }

    val operation = apolloRequest.operation
    val customScalarAdapters = apolloRequest.executionContext[CustomScalarAdapters]!!

    val body = buildJsonByteString {
      writeObject {
        name("query")
        value(operation.document())
        name("operationName")
        value(operation.name())
        name("variables")
        writeObject {
          operation.serializeVariables(this, customScalarAdapters, false)
          // Add your variables here
          name("appName")
          value("MyAppName")
        }
      }
    }
    return HttpRequest.Builder(HttpMethod.Post, serverUrl)
        .body(
            object : HttpBody {
              override val contentType = "application/json"
              override val contentLength = body.size.toLong()

              override fun writeTo(bufferedSink: BufferedSink) {
                bufferedSink.write(body)
              }
            }
        )
        .build()
  }
}

may new method added to Apollo client in the future that support variables in request body ?

That is very unlikely. As said before, sending extra fields in GraphQL variables is not standard. Is there a reason you cannot use a HTTP header or another way for this?