Join us for GraphQL Summit, October 10-12 in San Diego. Use promo code ODYSSEY for $400 off your pass.
Launch GraphOS Studio
You're viewing documentation for an upcoming version of this software. Switch to the latest stable version.

Using GraphQL variables in Apollo Kotlin

GraphQL supports passing values to your s with variables. This enables you to write a single query that you can reuse with multiple values (this is a recommended best practice).

In GraphQL, non-nullable s are required, and nullable variables are optional. However, because variables are rarely omitted in practice, Apollo Kotlin provides a mechanism to make variables non-optional in generated code. This makes the structure of generated code more straightforward.

Because you might still need to omit s, the default is to generate them as optional, but you can configure this (for specific variables or globally).

Consider the following GraphQL query with two nullable s:

query GetTodos($first: Int, $offset: Int) {
todos(first: $first, offset: $offset) {

Apollo Kotlin generates the following Kotlin code for this query:

class GetTodosQuery(
val first: Optional<Int?> = Optional.Absent,
val offset: Optional<Int?> = Optional.Absent

You can then selectively provide or omit values like so:

// Omit values for both variables
val query = GetTodosQuery(Optional.Absent, Optional.Absent)
// Provide null for both variables
val query = GetTodosQuery(Optional.Present(null), Optional.Present(null))
// Send explicit values for both variables
val query = GetTodosQuery(Optional.Present(100), Optional.Present(0))

Making nullable variables non-optional

To disable optional s globally, update your Gradle config like so:

apollo {
service("service") {
// ...

If you do, in the case of the GetTodos query shown above, Apollo Kotlin now generates the following code:

class GetTodosQuery(val first: Int?, val offset: Int?)

This makes the calling code less verbose to use:

// Provide null for both variables
val query = GetTodosQuery(null, null)
// Send explicit values for both variables
val query = GetTodosQuery(100, 0)

If you pass null as the value for either of these s, Apollo Kotlin sends null to the server as the value of that variable instead of omitting it entirely.

Although doing this can simplify your code in most cases, you might still need to omit s for certain s. To achieve this, you can allow optional variables on a case-by-case basis with the @optional :

query GetTodos($first: Int @optional, $offset: Int @optional) {
todos(first: $first, offset: $offset) {

In this case, Apollo Kotlin generates code with Optional for only these specific s.

Error handling
Edit on GitHubEditForumsDiscord