GraphQL Variables & Operation Selection

---

Passing Scalar Variables

Variables avoid string concatenation and guard against injection issues:

String userName;
bool active = false;

client.graphql("/graphql")
    .query("query GetUser($id: ID!, $online: Boolean) { user(id: $id, online: $online) { name } }")
    .variable("id", "usr_9912")
    .variable("online", true)
    .getData("user.name", &userName);

---

Struct Variables with REST_JSON_MAP

Custom C++ structs can be passed as variables directly:

struct SensorTelemetry {
  float temp;
  float pressure;
  int battery;

  REST_JSON_MAP(
    REST_FIELD(temp),
    REST_FIELD(pressure),
    REST_FIELD(battery)
  )
};

SensorTelemetry data{24.2f, 1013.25f, 98};

client.graphql("/graphql")
    .mutation("mutation Log($input: TelemetryInput!) { record(data: $input) { id } }")
    .variable("input", data);

---

Multi-Operation Documents and operationName

When a single query document contains multiple operations, select which one to execute:

const char* doc =
    "query GetProfile { profile { name } }\n"
    "query GetConfig { config { refreshRate } }";

int rate = 0;

client.graphql("/graphql")
    .document(doc)
    .operationName("GetConfig")
    .getData("config.refreshRate", &rate);