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Schema & Type System

Schema definition language Object types Scalar types Non-null types List types Enums Interfaces Union types Input object types Schema root operation types

Fields & Arguments

Field definitions Field arguments Default argument values Field aliases Nested selections Descriptions and documentation Deprecated fields Custom scalar declarations Resolver field shape Selection-set validation

Queries

Basic query operation Named query operations Operation variables Variable default values Multiple root fields Nested object queries Query aliases Arguments in queries Introspection __typename Introspection __schema

Fragments & Directives

Named fragments Inline fragments Fragment type conditions Fragment variables pattern @include directive @skip directive Custom directives Directive locations Reusable selection sets Interface fragment matching

Mutations

Basic mutation operation Mutation input objects Mutation payload types Multiple mutation fields Mutation variables Create mutation pattern Update mutation pattern Delete mutation pattern Mutation error payloads Optimistic response shape

Subscriptions

Subscription operation Subscription payloads Subscription arguments Subscription variables Event filtering pattern Single root subscription rule WebSocket subscription shape Live event payloads Subscription authorization Subscription cleanup semantics

Errors, Security & Performance

Field-level errors Partial data with errors Null bubbling Authentication context Authorization at field level Query depth limiting Query complexity limiting Persisted queries N+1 query problem DataLoader batching pattern

Schema Evolution & Federation

Backward-compatible schema changes Deprecation workflow Adding optional fields Changing nullability safely Schema versioning strategy Federation @key Federation @external Federation @requires Federation entity references Gateway composition concepts

GraphQL Complete Course / Fragments & Directives

Interface fragment matching

Learn Interface fragment matching in GraphQL through the exact construct, a dedicated example, a boundary case, and a mastery check.

10 min read • Intermediate

Interface fragment matching is an atomic GraphQL lesson inside Fragments & Directives. The example uses the specific syntax, command, API, instruction, or language rule named by this lesson.

Study the construct itself, then change one relevant input and predict the result before running it. That keeps this lesson focused on Interface fragment matching rather than on generic GraphQL syntax.

Topic-specific example

graphql-04-10.graphql

graphql Try It Live

query { nodes { id ... on User { email } ... on Product { price } } }

Edge case / engineering note

Validate Interface fragment matching against the schema and test nullable/error behavior. GraphQL may return partial data, so distinguish validation errors from resolver-time errors.

Content source & attribution

Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

Interface fragment matching Mastery Check →

Reusable selection sets

Basic mutation operation