Object types and input types in NestJS - Performance & Optimization

Performance: Object types and input types

MEDIUM IMPACT

This concept affects server response time and client rendering speed by influencing how data is validated and transformed before processing.

Defining GraphQL object and input types for API requests

NestJS

import { ObjectType, Field, InputType } from '@nestjs/graphql';

@ObjectType()
export class User {
  @Field()
  name: string;

  @Field()
  age: number;
  // password field omitted from output type
}

@InputType()
export class CreateUserInput {
  @Field()
  name: string;

  @Field()
  age: number;

  @Field()
  password: string; // only in input type
}

Separating input and output types avoids sending sensitive data to clients and reduces payload size.

📈 Performance GainSmaller payloads improve network speed and reduce client rendering workload.

Defining GraphQL object and input types for API requests

NestJS

import { ObjectType, Field, InputType } from '@nestjs/graphql';

@ObjectType()
export class User {
  @Field()
  name: string;

  @Field()
  age: number;

  @Field()
  password: string; // included in output type
}

@InputType()
export class CreateUserInput {
  @Field()
  name: string;

  @Field()
  age: number;

  @Field()
  password: string;
}

Including sensitive fields like password in output object types causes unnecessary data exposure and larger payloads.

📉 Performance CostIncreases payload size, causing slower network transfer and longer client rendering times.

Performance Comparison

Pattern	Payload Size	Network Transfer	Client Parsing	Verdict
Including sensitive fields in output types	Large	Slower	More CPU	[X] Bad
Separating input and output types properly	Small	Faster	Less CPU	[OK] Good

Rendering Pipeline

Object and input types define the shape of data sent and received. Proper separation reduces data size, which speeds up network transfer and lowers client rendering time.

→Network Transfer

→Client Parsing

→Client Rendering

⚠️ BottleneckNetwork Transfer due to payload size

Core Web Vital Affected

INP

This concept affects server response time and client rendering speed by influencing how data is validated and transformed before processing.

Optimization Tips

1Always separate input types from output object types in GraphQL schemas.

2Exclude sensitive or unnecessary fields from output types to reduce payload size.

3Use input types to validate and accept data without exposing it back to clients.

Performance Quiz - 3 Questions

Why should sensitive fields like passwords be excluded from GraphQL output object types?

A To make the code shorter

B To reduce payload size and avoid exposing sensitive data

C To increase server CPU usage

D To make input types larger

DevTools: Network

How to check: Open DevTools, go to Network tab, inspect GraphQL request and response payload sizes.

What to look for: Look for smaller response sizes and faster transfer times indicating efficient object type usage.

Practice

1. What is the main purpose of using @ObjectType() in NestJS GraphQL?

easy

A. To define the shape of data returned by queries and mutations

B. To define the shape of data clients send to the server

C. To create database entities automatically

D. To handle HTTP request validation

Solution

1. Step 1: Understand the role of @ObjectType()

   This decorator is used to define the structure of data that GraphQL queries and mutations return to clients.

2. Step 2: Differentiate from input types

   @InputType() is used for data clients send, while @ObjectType() is for data sent back to clients.

3. Final Answer:

   To define the shape of data returned by queries and mutations -> Option A

4. Quick Check:

   ObjectType = output data shape [OK]

Hint: ObjectType decorates output data, InputType decorates input data [OK]

Common Mistakes:

• Confusing @ObjectType() with @InputType()
• Thinking @ObjectType() creates database tables
• Assuming @ObjectType() validates HTTP requests

2. Which of the following is the correct way to define an input type in NestJS GraphQL?

easy

A. @ObjectType() class CreateUserInput { name: string; }

B. @InputType() interface CreateUserInput { name: string; }

C. @InputType() class CreateUserInput { @Field() name: string; }

D. @Input() class CreateUserInput { name: string; }

Solution

1. Step 1: Identify correct decorator and syntax

   Input types require the @InputType() decorator and fields must be decorated with @Field() to expose them to GraphQL.

2. Step 2: Check class vs interface usage

   Input types must be classes, not interfaces, to work with decorators in NestJS.

3. Final Answer:

   @InputType() class CreateUserInput { @Field() name: string; } -> Option C

4. Quick Check:

   InputType + @Field + class = correct input type [OK]

Hint: Input types need @InputType() and @Field() on class properties [OK]

Common Mistakes:

• Using @ObjectType() instead of @InputType()
• Using interfaces instead of classes for input types
• Omitting @Field() decorator on fields

3. Given the following code, what will be the GraphQL output type for the user query?

@ObjectType()
class User {
  @Field()
  id: string;

  @Field()
  name: string;
}

@Resolver()
class UserResolver {
  @Query(() => User)
  user() {
    return { id: '1', name: 'Alice' };
  }
}

medium

A. An error because id is not a number

B. A User object with fields id and name

C. A list of User objects

D. Null because no data source is connected

Solution

1. Step 1: Analyze the @ObjectType and @Field decorators

   The User class defines two fields, id and name, both exposed to GraphQL via @Field().

2. Step 2: Check the resolver return and query type

   The user query returns an object matching User shape with id and name strings, matching the GraphQL type.

3. Final Answer:

   A User object with fields id and name -> Option B

4. Quick Check:

   Query returns User object with id and name [OK]

Hint: Return object matches @ObjectType class shape for query output [OK]

Common Mistakes:

• Expecting type errors for string id when GraphQL expects string
• Assuming query returns a list without @Query(() => [User])
• Thinking null is returned without data source

4. Identify the error in this input type definition:

@InputType()
class UpdateUserInput {
  name: string;
  @Field()
  age: number;
}

medium

A. Missing @Field() decorator on the 'name' property

B. Cannot use number type in input types

C. Class must be decorated with @ObjectType() instead

D. Input types cannot have more than one property

Solution

1. Step 1: Check decorators on class properties

   In GraphQL input types, each field must have the @Field() decorator to be exposed.

2. Step 2: Identify missing decorator

   The 'name' property lacks the @Field() decorator, so it won't be part of the GraphQL input type.

3. Final Answer:

   Missing @Field() decorator on the 'name' property -> Option A

4. Quick Check:

   All input fields need @Field() [OK]

Hint: Every input field needs @Field() decorator [OK]

Common Mistakes:

• Forgetting @Field() on some properties
• Confusing @InputType() with @ObjectType()
• Thinking number types are invalid in input types

5. You want to create a mutation to update a user's profile with optional fields. Which approach correctly defines the input type to allow optional fields in NestJS GraphQL?

@InputType()
class UpdateUserInput {
  @Field({ nullable: true })
  name?: string;

  @Field({ nullable: true })
  age?: number;
}

hard

A. Use @ObjectType() instead of @InputType() for mutations

B. Remove '?' and set default values instead of nullable

C. Make all fields required and handle optional logic in resolver

D. Use @Field({ nullable: true }) and optional properties with '?' to allow partial updates

Solution

1. Step 1: Understand optional fields in GraphQL input types

   To allow optional fields, use { nullable: true } in @Field() and mark properties optional with '?'.

2. Step 2: Confirm correct decorator usage

   Use @InputType() for input data in mutations, not @ObjectType().

3. Final Answer:

   Use @Field({ nullable: true }) and optional properties with '?' to allow partial updates -> Option D

4. Quick Check:

   Nullable fields + optional properties = optional input fields [OK]

Hint: Use nullable:true and '?' for optional input fields [OK]

Common Mistakes:

• Using @ObjectType() for input types
• Not marking fields nullable for optional inputs
• Making all fields required and complicating resolver logic