Nullability

Rust expresses nullability with Option<T> and collection element types. gurafi maps that to GraphQL wrappers and checks explicit overrides at build time.

#The default mapping

Objects, interfaces and unions are nullable by default because their derived OutputType is a plain named type. Wrap them in Option when the resolver can return no value; the GraphQL type is already nullable, so Option<User> and User print the same type. Use non_null() when an object field must never be null.

Lists are non-null by default. The item type follows the Rust item type.

#Default nullability

Rust's idiomatic mapping is driven by Option: a non-Option value cannot be null, so it is non-null; Option<T> is nullable. Use Option<T> whenever the resolver can return None, and non_null() only when the model type itself requires it. The compiler and the build-time checks keep the GraphQL wrapper honest.

#Explicit overrides

FieldConfig can adjust the wrappers when the Rust type is truthful:

.field(...).nullable()        // remove the field's outer !
.field(...).non_null()        // add !, only if the Rust type is not Option
.field(...).nullable_items()  // [T!]! -> [T]!
.field(...).non_null_items()  // [T]! -> [T!]!

Overrides are validated:

• A nullable Rust position cannot be made non-null. Option<String> cannot become String!.
• A list shape must match the Rust collection. Vec<String> cannot become String!.
• A non-list cannot use nullable_items / non_null_items.
• non_null_items trusts that the collection cannot contain None; use it only when that is true for the Rust type, or keep Option items and accept [T]!.

Use .returns::<T>() / .as_type::<T>() to replace the named type while preserving the nullability contract. field_ref_type and as_dynamic similarly verify wrappers.

#Inputs

Input fields use the same mapping:

• Option<T> is optional and nullable.
• A non-Option field without a default is required and non-null.
• A default does not replace an explicit null.
• #[graphql(default = ...)] makes an omitted field use the default.

#Null propagation

If a non-null field resolves to null, the executor propagates null to the nearest nullable parent, exactly as the GraphQL specification requires. Errors are collected at the field's path. Use Option in the model to make null a legal result rather than an error.

#Next

• Fields
• Input objects
• Type inference