Info argument in GraphQL

Introduction

The info argument helps you understand what data the client wants in a GraphQL request. It tells your server exactly which fields to fetch and return.

When you want to get only the requested fields from a database to save time and resources.

When building a GraphQL resolver that needs to know which fields the client asked for.

When optimizing queries to avoid fetching unnecessary data.

When you want to pass the requested fields to another function or service for processing.

Syntax

GraphQL

function resolver(parent, args, context, info) {
  // use info to get requested fields
}

The info argument is the fourth parameter in a resolver function.

It contains details about the GraphQL query, including the fields requested by the client.

Examples

Logs the name of the field being resolved.

GraphQL

const resolver = (parent, args, context, info) => {
  console.log(info.fieldName);
};

Extracts the list of fields the client requested in the query.

GraphQL

const requestedFields = info.fieldNodes[0].selectionSet.selections.map(field => field.name.value);

Sample Program

This example shows a GraphQL query for a user requesting only id and name. The resolver uses the info argument to return only those fields.

GraphQL

const { graphql, buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    user(id: ID!): User
  }
  type User {
    id: ID
    name: String
    email: String
  }
`);

const root = {
  user: (parent, args, context, info) => {
    // Simulated database record
    const userData = { id: '1', name: 'Alice', email: '[e-mail]' };

    // Get requested fields
    const requestedFields = info.fieldNodes[0].selectionSet.selections.map(field => field.name.value);

    // Return only requested fields
    const result = {};
    requestedFields.forEach(field => {
      if (userData.hasOwnProperty(field)) {
        result[field] = userData[field];
      }
    });
    return result;
  }
};

const query = `{
  user(id: "1") {
    id
    name
  }
}`;

graphql(schema, query, root).then(response => {
  console.log(JSON.stringify(response.data, null, 2));
});

Important Notes

The info argument helps avoid fetching data you don't need, improving performance.

It can be complex to parse deeply nested queries, but libraries exist to help.

Always check if the requested field exists in your data before returning it.

Summary

The info argument tells your resolver which fields the client wants.

Use info to return only requested data and save resources.

It is the fourth parameter in every GraphQL resolver function.

Practice

1. What is the purpose of the info argument in a GraphQL resolver?

easy

A. It stores the database connection details.

B. It contains the user's authentication token.

C. It tells the resolver which fields the client requested.

D. It defines the schema of the GraphQL server.

Solution

1. Step 1: Understand the role of resolver arguments

   Resolvers receive arguments like parent, args, context, and info. Each has a specific role.

2. Step 2: Identify what info provides

   The info argument contains details about the query, including which fields the client requested.

3. Final Answer:

   It tells the resolver which fields the client requested. -> Option C

4. Quick Check:

   Info argument = requested fields [OK]

Hint: Info shows requested fields to optimize data fetching [OK]

Common Mistakes:

• Confusing info with context or args
• Thinking info holds authentication data
• Assuming info defines schema

2. Which of the following is the correct way to include the info argument in a GraphQL resolver function?

easy

A. resolver(parent, args, context, info) { ... }

B. resolver(args, parent, info, context) { ... }

C. resolver(context, info, args, parent) { ... }

D. resolver(info, parent, args, context) { ... }

Solution

1. Step 1: Recall the standard resolver signature

   The standard order is (parent, args, context, info) in GraphQL resolvers.

2. Step 2: Match the correct order

   resolver(parent, args, context, info) { ... } matches this order exactly, making it the correct syntax.

3. Final Answer:

   resolver(parent, args, context, info) { ... } -> Option A

4. Quick Check:

   Resolver args order = parent, args, context, info [OK]

Hint: Remember resolver args order: parent, args, context, info [OK]

Common Mistakes:

• Mixing up the order of arguments
• Placing info before context
• Omitting info argument

3. Given this resolver snippet, what will info.fieldNodes[0].selectionSet.selections.map(f => f.name.value) return if the client queries { user { id name } }?

medium

A. ["id", "name"]

B. ["user"]

C. ["id"]

D. An empty array []

Solution

1. Step 1: Understand the query structure

   The client requests the fields id and name inside user.

2. Step 2: Analyze the info.fieldNodes access

   info.fieldNodes[0].selectionSet.selections lists the fields requested inside user, which are id and name.

3. Final Answer:

   ["id", "name"] -> Option A

4. Quick Check:

   info.fieldNodes selections = requested fields [OK]

Hint: info.fieldNodes lists requested fields inside current resolver [OK]

Common Mistakes:

• Returning parent field name instead of subfields
• Confusing selectionSet with fieldNodes
• Expecting only one field instead of all requested

4. You wrote this resolver: function resolver(parent, args, context) { return info.fieldNodes; }. Why does this cause an error?

medium

A. You cannot access fieldNodes inside resolvers.

B. The resolver is missing the info argument in its parameters.

C. The info argument must be the first parameter.

D. Resolvers cannot return objects like fieldNodes.

Solution

1. Step 1: Check resolver parameters

   The resolver only has three parameters: parent, args, context. It lacks the fourth parameter info.

2. Step 2: Understand usage of info

   Since info is not declared, trying to use it causes a reference error.

3. Final Answer:

   The resolver is missing the info argument in its parameters. -> Option B

4. Quick Check:

   Missing info param = error [OK]

Hint: Always include info as fourth parameter to use it [OK]

Common Mistakes:

• Forgetting to add info parameter
• Assuming info is global or in context
• Misordering resolver parameters

5. You want your resolver to return only the fields requested by the client to save resources. Which approach using the info argument is best?

hard

A. Fetch all fields but filter results after sending to client.

B. Ignore info and always fetch all fields from the database.

C. Use args to guess which fields the client wants.

D. Use info.fieldNodes to find requested fields and fetch only those from the database.

Solution

1. Step 1: Understand the goal

   The goal is to fetch only requested fields to save resources.

2. Step 2: Use info to get requested fields

   info.fieldNodes provides the exact fields the client asked for, so you can fetch only those.

3. Step 3: Compare options

   Use info.fieldNodes to find requested fields and fetch only those from the database. uses info correctly. Options B, C, and D either waste resources or guess incorrectly.

4. Final Answer:

   Use info.fieldNodes to find requested fields and fetch only those from the database. -> Option D

5. Quick Check:

   Use info to fetch requested fields only [OK]

Hint: Fetch only requested fields using info to save resources [OK]

Common Mistakes:

• Fetching all data regardless of request
• Using args instead of info for fields
• Filtering after fetching all data