Expose stored object properties
A parent object already contains a scalar field with the same name as the GraphQL field.
GraphQL · Function
defaultFieldResolver
defaultFieldResolver is the conventional behavior used by many GraphQL libraries when no field resolver is supplied: read the same-named property from the parent object and return it. It suits simple fields whose values are already present on that object.
How it works
GraphQL’s default field behavior resolves a field by reading a property with the same name from the parent object when no custom resolver is supplied. This is useful for simple fields whose response value is already present on the parent object.
Returns
The value produced for the field; for a trivial resolver, the same-named property from the parent object.
Key points
- Each selected field conceptually acts like a function or method on the value produced by the preceding field.
- GraphQL servers associate fields with resolver behavior that produces their values.
- Execution invokes the field’s resolver to obtain the value used for the next stage.
- The trivial-resolver convention reads and returns a parent property whose name matches the field.
- Resolved values are stored in the response map using the field name or its alias as the key.
Common mistakes
- This behavior is a library convention rather than a universal GraphQL specification requirement; verify how the server library implements omitted resolvers.
Example: Same-name property resolution
const user = { name: "Ada" };
const result = user.name;
console.log(result); // AdaA trivial resolver can return a same-named property from the parent object.
When to use it
Reduce boilerplate for simple types
A type has several straightforward fields that require no computation or data fetching.
Resolve nested object data
A nested selection reads fields directly from an object returned by an earlier resolver.
Interview questions
QWhat is a resolver, and how does the default behavior work?
A resolver is the function backing a GraphQL field. During execution, GraphQL calls the resolver for the field to produce the next value; for a trivial field, many libraries can instead read a same-named property from the parent object.
Follow-up: What happens when the field has a custom resolver? The custom resolver is used to compute the field’s value instead of relying on the same-name property convention.
QWhen can a resolver be omitted?
A trivial resolver is appropriate when the value is already stored on the parent object under the GraphQL field’s name. In that case, no explicit resolver is needed in libraries that support this convention.
Follow-up: When should an explicit resolver be preferred? Use one when the value requires computation, arguments, external data access, or a property name different from the schema field.
QHow does a resolved field appear in the GraphQL response?
Field execution produces values that are placed into a response map under the field name or alias. The resolved value then supplies the next part of the result structure.
Follow-up: What determines the response key? An alias becomes the response key; without an alias, the field name is used.
Related
resolverfield resolvertrivial resolverQueryMutationSubscriptionalias