NestJS/Express: Case-Insensitive Body Fields - node.js

Question

I'm struggling to make the fields of my request DTOs case insensitive.
export class ExampleDto {
dateOfBirth?: string
}
Now I want to accept
{ "dateofbirth": "19880101" }
{ "dateOfBirth": "19880101" }
{ "DATEOFBIRTH": "19880101" }
My first thought was to implement a middleware which just looks at the incoming body and "extends it" with lower & upper case mappings for all incoming fields.
But that doesn't meet my requirements due to camel case, which I definitely want to keep as the default.
Any ideas on how to do this?

Answer 1

You could create a custom Pipe where you try the different options and finally return the Dto instance:
export class CaseInsensitiveExampleDtoPipe implements PipeTransform{
transform(body: any, metadata: ArgumentMetadata): ExampleDto {
const dto = new ExampleDto();
dto.dateOfBirth = body.dateOfBirth || body.dateofbirth || body.DATEOFBIRTH;
return dto;
}
In your controller you can then use it as follows:
#UsePipes(new CaseInsensitiveExampleDtoPipe())
async postNewExample(#Body() exampleDto: ExampleDto) {
// ...
}

Answer 2

Since JavaScript properties start existing after their initialization, you cannot "see" the definition of dateOfBirth?: string and therefor you won't be able to match it against the received JSON.
A possible solution for that is to enforce the creation of the properties of all of your DTO's with a constructor:
export class ExampleDto {
dateOfBirth: string
constructor(dateOfBirth: string){
this.dateOfBirth = dateOfBirth;
}
}
Then, you'll be able to iterate over the ExampleDto's properties and match them with a pipe (the received type can be derived from metadata):
#Injectable()
export class IgnoreCasePipe implements PipeTransform {
transform(value: any, metadata: ArgumentMetadata) {
const dto = new metadata.metatype;
const dtoKeys = Object.getOwnPropertyNames(dto);
Object.keys(value).forEach(key => {
const realKey = dtoKeys.find(dtoKey => dtoKey.toLocaleLowerCase() === key.toLocaleLowerCase());
if (realKey) {
dto[realKey] = value[key];
}
});
return dto;
}
}
Either inject it globally in main.ts or wherever it's needed - just bear in mind that you'll need to create a constructor for each DTO.
Note: this would work for a single-level class. If you want to support something like people: PersonDto[] in your classes then you'll need to recursively find all of the nested keys and match them - something like this.