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This page describes concepts that are shared across all Cosmo Streams handlers and apply to every available hook.

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Operation Variables

If your operation defines variables, you can access them through the Variables method on the OperationContext interface. 
variables := ctx.Operation().Variables()

subscription($customerId: Int!) {
  orderUpdates(customerId: $customerId) {
    id
  }
}
Example variables payload: 
{
  "customerId": 123
}
Inside your handler, you can retrieve the variables using the Variables method: 
variables := ctx.Operation().Variables()
customerId := variables.Get("customerId").GetInt() // = 123

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Operation Arguments

If no variables are defined in the operation, or if you do not control the variables, you can access arguments directly via the OperationContext interface. 
arguments := ctx.Operation().Arguments()
Consider an operation that defines multiple arguments: 
subscription {
  orderUpdates(customerId: "123", status: PENDING) {
    id
    items(first: 5, sortBy: "price") { name }
  }
}
To access the customerId argument of the subscription field, use the Get method: 
customerId := ctx.Operation().Arguments().Get("orderUpdates", "customerId").GetStringBytes()
Because orderUpdates is the root field, you can also resolve the field name dynamically: 
// For OnPublishEvent handler
rootFieldName := ctx.PublishEventConfiguration().RootFieldName()

// For OnReceiveEvent and SubscriptionOnStart handler
rootFieldName := ctx.SubscriptionEventConfiguration().RootFieldName()

customerId := ctx.Operation().Arguments().Get(rootFieldName, "customerId").Value()
To access arguments on nested fields, such as the sortBy argument of the items field, use dot notation to reference the nested path. 
sortBy := ctx.Operation().Arguments().Get("orderUpdates.items", "sortBy").GetStringBytes()
When a field uses an alias, the alias must be used as the key when accessing its arguments. 
subscription {
  orderUpdates(customerId: "123", status: PENDING) {
    id
    cheapestItems: items(first: 3, sortBy: "price") { name }
    newestItems: items(first: 3, sortBy: "createdAt") { name }
  }
}

cheapestItemsSortBy := ctx.Operation().Arguments().Get("orderUpdates.cheapestItems", "sortBy").GetStringBytes()
newestItemsSortBy := ctx.Operation().Arguments().Get("orderUpdates.newestItems", "sortBy").GetStringBytes()
You can also work with more complex argument types, such as arrays and input objects. 
subscription {
  orderUpdates(statuses: ["pending", "shipped"], filter: { minTotal: 100, currency: "USD" }) {
    id
  }
}

arguments := ctx.Operation().Arguments()

statuses := arguments.Get("orderUpdates", "statuses").GetArray()
filter := arguments.Get("orderUpdates", "filter").GetObject()
minTotal := filter.Get("minTotal").GetInt()
currency := filter.Get("currency").GetStringBytes()