Schema definition in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Schema decorator from Mongoose.

NestJS

import { [1] } from '@nestjs/mongoose';

Drag options to blanks, or click blank then click option'

ASchema

BModule

CController

DInjectable

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Module or Controller instead of Schema

Forgetting to import from '@nestjs/mongoose'

The @Schema decorator is imported from @nestjs/mongoose to define a Mongoose schema in NestJS.

2fill in blank

medium

Complete the code to define a schema class named User.

NestJS

@[1]()
export class User {}

Drag options to blanks, or click blank then click option'

AController

BSchema

CInjectable

DModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Injectable or @Controller instead of @Schema

Missing parentheses after the decorator

The @Schema() decorator marks the class as a Mongoose schema in NestJS.

3fill in blank

hard

Fix the error in the property decorator to define a schema property.

NestJS

import { Prop } from '@nestjs/mongoose';

@Schema()
export class Product {
  @[1]()
  name: string;
}

Drag options to blanks, or click blank then click option'

AProp

BProperty

CSchema

DField

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Property or @Field which are not valid in NestJS Mongoose schemas

Forgetting to import Prop

The @Prop() decorator defines a property in the Mongoose schema.

4fill in blank

hard

Fill both blanks to create a schema factory for the User class.

NestJS

export const UserSchema = [1](User, [2]);

Drag options to blanks, or click blank then click option'

ASchemaFactory.createForClass

BUser

C{ timestamps: true }

DProp

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name instead of the factory method

Passing the class name as second argument instead of options object

SchemaFactory.createForClass(User, { timestamps: true }) creates a Mongoose schema with timestamps enabled.

5fill in blank

hard

Fill all three blanks to define a schema with a required string property 'title'.

NestJS

@Schema()
export class Book {
  @[1]({ required: [2] })
  [3]: string;
}

Drag options to blanks, or click blank then click option'

AProp

Btrue

Ctitle

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using false instead of true for required

Missing the property name or using wrong decorator

The @Prop({ required: true }) decorator marks the 'title' property as required in the schema.

Practice

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

easy

A. To define the structure and rules of a data model

B. To create a new controller

C. To handle HTTP requests

D. To style components

Solution

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

   @Schema() is used to define how data should be structured and validated in NestJS models.

2. Step 2: Compare with other options

   Creating controllers, handling HTTP requests, and styling components are unrelated to schema definition.

3. Final Answer:

   To define the structure and rules of a data model -> Option A

4. Quick Check:

   Schema decorator defines data structure [OK]

Hint: Remember: @Schema() sets data shape, not controllers or styles [OK]

Common Mistakes:

• Confusing @Schema() with controller decorators
• Thinking @Schema() handles HTTP logic
• Mixing schema with UI styling

2. Which of the following is the correct way to define a string property named title in a NestJS schema?

easy

A. @Prop() title: number;

B. @Prop() title: string;

C. @Prop() title = 123;

D. @Prop() title: boolean;

Solution

1. Step 1: Identify the correct type for a string property

   The property title should be of type string to hold text data.

2. Step 2: Check the syntax of @Prop()

   The correct syntax is @Prop() title: string; which declares a string property.

3. Final Answer:

   @Prop() title: string; -> Option B

4. Quick Check:

   String property uses type string [OK]

Hint: Use @Prop() with correct TypeScript type for properties [OK]

Common Mistakes:

• Using wrong types like number or boolean for string data
• Assigning values instead of declaring types
• Missing @Prop() decorator

3. Given this schema snippet:

@Schema()
export class Book {
  @Prop()
  author: string;

  @Prop({ required: true })
  pages: number;
}

What happens if you try to save a Book without pages?

medium

A. The save will throw a syntax error

B. The save will succeed and pages will be undefined

C. The save will succeed and pages will default to 0

D. The save will fail because pages is required

Solution

1. Step 1: Understand the required: true option

   The pages property is marked as required, so it must be provided when saving.

2. Step 2: Predict behavior when missing required property

   Omitting pages causes validation to fail and the save operation to be rejected.

3. Final Answer:

   The save will fail because pages is required -> Option D

4. Quick Check:

   Required props must be present [OK]

Hint: Required props block save if missing [OK]

Common Mistakes:

• Assuming missing required props default silently
• Confusing validation errors with syntax errors
• Ignoring the required option in @Prop()

4. Identify the error in this schema definition:

@Schema()
export class User {
  @Prop({ type: String })
  age: number;
}

medium

A. No error, this is correct

B. Missing @Schema() decorator

C. The type in @Prop() does not match the property type

D. Property name cannot be 'age'

Solution

1. Step 1: Compare @Prop() type and property type

   The decorator says type: String but the property is declared as number.

2. Step 2: Understand type mismatch consequences

   This mismatch can cause runtime errors or incorrect schema behavior.

3. Final Answer:

   The type in @Prop() does not match the property type -> Option C

4. Quick Check:

   Decorator type must match property type [OK]

Hint: Match @Prop() type with property type exactly [OK]

Common Mistakes:

• Using wrong type in @Prop() options
• Ignoring type mismatch warnings
• Assuming property name causes errors

5. How would you define a schema for a Product with a required name (string), optional price (number), and a default inStock (boolean) set to true?

hard

A. @Schema()
export class Product {
@Prop({ required: true })
name: string;

@Prop()
price?: number;

@Prop({ default: true })
inStock: boolean;
}

B. @Schema()
export class Product {
@Prop()
name: string;

@Prop({ required: true })
price: number;

@Prop({ default: false })
inStock: boolean;
}

C. @Schema()
export class Product {
@Prop({ required: true })
name: number;

@Prop()
price: string;

@Prop({ default: true })
inStock: boolean;
}

D. @Schema()
export class Product {
@Prop({ required: true })
name: string;

@Prop({ default: 0 })
price: number;

@Prop()
inStock: boolean;
}

Solution

1. Step 1: Define required name as string

   Use @Prop({ required: true }) name: string; to make name mandatory.

2. Step 2: Define optional price as number

   Use @Prop() price?: number; to allow price to be optional.

3. Step 3: Define inStock with default true

   Use @Prop({ default: true }) inStock: boolean; to set default value.

4. Final Answer:

   Schema with required name (string), optional price (number), and inStock default true -> Option A

5. Quick Check:

   Required, optional, default props set properly [OK]

Hint: Use required, optional ?, and default in @Prop() [OK]

Common Mistakes:

• Mixing types for properties
• Forgetting to mark required props
• Setting wrong default values