Array parameters are not deserialized/validated properly

[marshall007]

Given the following decorated parameters on a controller method:

@QueryParam('fields') fields: string[],
@QueryParam('numbers') numbers: number[]

... the behavior of arrays in query parameters is inconsistent. Namely single values are not coerced to an array and the inner values are not coerced or validated against the appropriate type. Some examples:

// GET ?fields=name
// -> ParameterParseJsonError: Value (\"name\") cannot be parsed to JSON

// GET ?fields=foo&fields=bar
console.log(fields) // -> [ "foo", "bar" ]

// GET ?numbers=1&numbers=2
console.log(numbers) // -> [ "1", "2" ] (works, but not deserialized)

[marshall007]

The second part of this issue regarding type coercion for nested values may not actually be possible. It seems the only type metadata available for array primitives is Array (see microsoft/TypeScript#3015) so we can't know the inner type.

@pleerock are there any other options here? I think class-transformer has a Type decorator to handle the array case? It will be kinda unfortunate if we had to make that a parameter of the Param decorators.

[pleerock]

Right, its not possible to automatically find type of "string[]". You can do it with class-transformer, but your type should be object and inside it you should have your string[] with type set.

Alternative could be to have type option in QueryParam options: @QueryParam("fields", { type: String }), but this is only needed for arrays, Im not sure if this functionality worth it.

[MichalLytek]

You can do it with class-transformer, but your type should be object and inside it you should have your string[] with type set.

So it looks like all the problems with class-validator and class-transformer comes to one solution - #122 😉 I will try to look at the source code to see how much complicated is the implementation of this feature and whether I could help and contribute.

[pleerock]

I'll close it. If someone interested in fixing this issue feel free to create a PR. But I personally think it does not worth it. Better to create object and let class-transfromer to perform proper transformation directly into the object, instead of having each array in a separate query parameter.

[github-actions]

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