Code generation from schema in GraphQL - Step-by-Step Execution

Concept Flow - Code generation from schema

Start with GraphQL Schema

↓

Parse Schema Definitions

↓

Generate TypeScript Types

↓

Generate Query and Mutation Functions

↓

Output Code Files

↓

End

The process starts with a GraphQL schema, which is parsed to generate TypeScript types and query/mutation functions, then outputs code files.

Execution Sample

GraphQL

schema {
  query: Query
}
type Query {
  user(id: ID!): User
}
type User {
  id: ID!
  name: String
}

This schema defines a Query type with a user field that returns a User object by ID.

Execution Table

Step	Action	Input	Output
1	Parse schema	GraphQL schema text	AST (Abstract Syntax Tree) of schema
2	Generate TypeScript types	AST	TypeScript interfaces for Query and User
3	Generate query functions	AST	Functions to fetch user by ID
4	Write code files	Generated types and functions	Files: types.ts, queries.ts
5	End	All code generated	Code ready for use

💡 All schema parts processed and code files generated

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
schemaText	GraphQL schema string	GraphQL schema string	GraphQL schema string	GraphQL schema string	GraphQL schema string
AST	null	Parsed AST	Parsed AST	Parsed AST	Parsed AST
TypeScriptTypes	null	null	Generated interfaces	Generated interfaces	Generated interfaces
QueryFunctions	null	null	null	Generated functions	Generated functions
CodeFiles	empty	empty	empty	empty	Written files

Key Moments - 2 Insights

Why do we parse the schema before generating code?

Parsing converts the schema text into a structured AST, which is easier to analyze and use for generating accurate code, as shown in execution_table step 1.

What is the difference between TypeScript types and query functions generated?

TypeScript types define data shapes (step 2), while query functions are code to fetch data (step 3). Both are needed for type-safe API calls.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 2?

A Functions to fetch user by ID

B TypeScript interfaces for Query and User

C AST of schema

D Code files written

💡 Hint

Check the 'Output' column in row with Step 2 in execution_table

At which step are query functions generated?

A Step 3

B Step 1

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column in execution_table for generating query functions

If the schema changes, which variable in variable_tracker will be updated first?

A QueryFunctions

B TypeScriptTypes

C AST

D CodeFiles

💡 Hint

Parsing schema updates the AST first as shown in variable_tracker after Step 1

Concept Snapshot

Code generation from schema:
- Start with GraphQL schema text
- Parse schema into AST
- Generate TypeScript types from AST
- Generate query/mutation functions
- Output code files for use
This automates creating type-safe API code.

Full Transcript

Code generation from schema starts by taking the GraphQL schema text and parsing it into an abstract syntax tree (AST). This structured form makes it easier to analyze the schema. Next, TypeScript interfaces are generated to represent the data types defined in the schema, such as Query and User types. Then, functions to perform queries and mutations are created based on the schema fields. Finally, all generated code is written into files ready to be used in applications. This process ensures type safety and reduces manual coding errors.