Default value pipe in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Default Value Pipe in NestJS?

The Default Value Pipe sets a default value for a route parameter or query if the client does not provide one. It helps avoid undefined or missing values in handlers.

beginner

How do you apply the Default Value Pipe to a query parameter in NestJS?

You use it in the controller method parameter like this: <br>@Query('page', new DefaultValuePipe(1)) page: number<br>This means if 'page' is missing, it defaults to 1.

intermediate

Can the Default Value Pipe be combined with other pipes in NestJS? How?

Yes. You can chain pipes by passing them as separate arguments: <br>@Query('limit', new DefaultValuePipe(10), new ParseIntPipe()) limit: number<br>This sets a default and then converts to number.

beginner

What happens if the Default Value Pipe is not used and a query parameter is missing?

The parameter value will be undefined in the controller method, which may cause errors if not handled properly.

beginner

Write a simple example of a NestJS controller method using Default Value Pipe for a 'sort' query parameter with default 'asc'.

  @Get()
  getItems(@Query('sort', new DefaultValuePipe('asc')) sort: string) {
    return `Sorting items by ${sort}`;
  }

What does the Default Value Pipe do in NestJS?

A Blocks requests without parameters

B Sets a default value if the input is missing

C Transforms input to uppercase

D Validates the input format

The Default Value Pipe provides a fallback value when the client does not send a parameter.

How do you apply Default Value Pipe to a route parameter named 'id' with default 0?

A @Param('id', new DefaultValuePipe(0)) id: number

B @Query('id', new DefaultValuePipe(0)) id: number

C @Body('id', new DefaultValuePipe(0)) id: number

D @Param('id', ParseIntPipe) id: number

Route parameters use @Param decorator; DefaultValuePipe sets default if missing.

Which of these is a valid way to chain Default Value Pipe with ParseIntPipe?

A @Query('page', [new DefaultValuePipe(1), new ParseIntPipe()]) page: number

B @Query('page', ParseIntPipe, DefaultValuePipe) page: number

C @Query('page', new DefaultValuePipe(1)) page: number

D @Query('page', new DefaultValuePipe(1), new ParseIntPipe()) page: number

You can pass multiple pipes as separate arguments to the decorator.

If a query parameter is missing and no Default Value Pipe is used, what is the parameter value?

A undefined

B null

C empty string

D default value 0

Missing parameters are undefined unless a default is set.

Which decorator is used to access query parameters in NestJS?

A @Body()

B @Param()

C @Query()

D @Headers()

@Query() accesses query string parameters from the URL.

Explain how the Default Value Pipe improves handling of missing parameters in NestJS controllers.

Think about what happens when a client forgets to send a parameter.

Describe how to combine Default Value Pipe with other pipes like ParseIntPipe in a NestJS controller.

Consider the order of pipes and their roles.