Solution:Step 1: Understand nullability in GraphQLIn GraphQL, if a nullable object field like 'customer' resolves to null, but the query requests subfields on that field, it results in a runtime error because null cannot have fields.Step 2: Check which queries request subfields of 'customer'The quer

[Solved] In this schema:type Order { id: ID customer: Customer } type Customer { id: ID name: String }Which query will cause a runtime error if the resolver for 'customer' returns null? | GraphQL

GraphQL - Type Relationships

In this schema:

type Order { id: ID customer: Customer } type Customer { id: ID name: String }

Which query will cause a runtime error if the resolver for 'customer' returns null?

A{ order(id: "5") { id customer { name } } }

B{ order(id: "5") { id customer } }

C{ order(id: "5") { id } }

D{ order(id: "5") { customer } }

Step-by-Step Solution

Solution:

Step 1: Understand nullability in GraphQL
In GraphQL, if a nullable object field like 'customer' resolves to null, but the query requests subfields on that field, it results in a runtime error because null cannot have fields.
Step 2: Check which queries request subfields of 'customer'
The query { order(id: "5") { id customer { name } } } requests subfields on customer, causing the error if null. Others either don't query customer or query it without subfields.
Final Answer:
{ order(id: "5") { id customer { name } } } -> Option A
Quick Check:
Requesting subfields on null object causes errors = A [OK]

Quick Trick: Requesting subfields on null causes errors unless nullable [OK]

Common Mistakes:

Assuming null object fields never cause errors
Ignoring nullability in schema definitions
Thinking all queries handle null automatically

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In this schema:

Step 1: Understand nullability in GraphQL

Step 2: Check which queries request subfields of 'customer'

Final Answer:

Quick Check:

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