Day 2: Queries: Fetching Exactly What You Need | GraphQL in 5 Days

Query Arguments

Queries

# Basic query — only get what you need
query GetUsers {
  users {
    id
    name
    # Note: we're NOT requesting email
    # The server won't include it
  }
}

# Query with argument
query GetUser {
  user(id: "1") {
    name
    email
    posts {
      title
    }
  }
}

# Aliases: query same field twice with different args
query CompareUsers {
  alice: user(id: "1") { name email }
  bob: user(id: "2") { name email }
}

# Fragments: reusable field sets
fragment UserFields on User {
  id
  name
  email
}

query {
  users { ...UserFields }
}

Variables

# Variables make queries reusable
# Define in the query:
query GetUser($userId: ID!) {
  user(id: $userId) {
    name
    email
  }
}

# Pass variables separately:
{
  "userId": "1"
}

# With optional variables:
query SearchPosts($query: String, $limit: Int = 10) {
  searchPosts(query: $query, limit: $limit) {
    title
    body
  }
}

ℹ️

Variables are the right way to pass dynamic values. Never interpolate values directly into query strings — that's vulnerable to injection and prevents query caching on the server.

📝 Day 2 Exercise

Write Complex Queries

Day 2 Summary

Clients request only the fields they need — no over-fetching.
Aliases: alice: user(id: "1") — same field, different name, different arguments.
Fragments: fragment Name on Type { ...fields } — reuse field selections.
Variables: always pass dynamic values as variables, not inline in the query string.

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Day 1: Schema, Types, and Your First Query

Day 3: Mutations: Writing Data

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