Nest.js Multiple Query Parameters with Same Name

Question

Controller

@Get(')
test(
    @Param('accountId') accountId: string,
    @Query('propertyName') propertyNames: string[],
) {
    console.log(propertyNames);
}

Sample Request localhost:8000?propertyName=test2&propertyName=test3

Output:

[ 'test2', 'test3' ]

This works fine when I have multiple values, but when only one parameter is sent, it creates a string instead of an Array

Request: localhost:8000?propertyName=test3 Generates the output: test3 instead of [test3]

My current approach is to use (as per https://stackoverflow.com/a/4775737/5236575 )

propertyName = [].concat(propertyName)

to ensure the value is an array.

Is there a way to force Nest.js to parse the query parameters as a string array at all times as this is required in multiple places across controllers.

---

Note: ValdiationPipe: transform is set to true

app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));

Answer 1

Off the top of my head, you could use @Transform decorator from class-transformer to achieve that. You could move the logic of transforming a single string parameter to array with help of that decorator.