Default resolvers in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a default resolver in GraphQL?

A default resolver is the built-in function GraphQL uses to fetch the value of a field when no custom resolver is provided. It simply returns the property of the source object that matches the field name.

beginner

How does GraphQL's default resolver find the value for a field?

It looks for a property on the parent object with the same name as the field and returns its value directly.

intermediate

When would you need to write a custom resolver instead of relying on the default resolver?

When the data needs transformation, fetching from another source, or combining multiple fields, you write a custom resolver. The default resolver only returns existing properties as-is.

beginner

True or False: The default resolver can handle nested objects automatically.

True. If the field's value is an object, the default resolver returns it, and GraphQL continues resolving fields on that nested object.

beginner

What happens if the default resolver does not find a matching property on the source object?

It returns null or undefined, which means the field will have no value in the query result unless a custom resolver handles it.

What does the default resolver in GraphQL do when resolving a field?

A Returns the property of the source object matching the field name

B Always returns null

C Fetches data from a database automatically

D Transforms the data before returning

The default resolver returns the property on the source object that matches the field name.

When is a custom resolver necessary instead of using the default resolver?

A When data needs to be fetched from another source or transformed

B When the field name matches the source object property

C When the query is simple

D When the default resolver returns the correct value

Custom resolvers are needed when data requires fetching from other sources or transformation.

If a field's value is an object, how does the default resolver handle it?

A It throws an error

B It returns null

C It returns the object and GraphQL resolves nested fields automatically

D It converts the object to a string

The default resolver returns the object, allowing GraphQL to resolve nested fields.

What will the default resolver return if the source object does not have the requested field?

A An error message

B Null or undefined

C The entire source object

D A default string value

If the property is missing, the default resolver returns null or undefined.

Which of the following is NOT true about default resolvers?

A They handle nested objects by returning them

B They return the property matching the field name

C They are used when no custom resolver is defined

D They automatically fetch data from databases

Default resolvers do not fetch data from databases automatically; they just return existing properties.

Explain how GraphQL's default resolver works when resolving a field in a query.

Think about how GraphQL finds the value without custom code.

Describe a situation where you would need to write a custom resolver instead of relying on the default resolver.

When the data is not directly available as a simple property.