Feature Request: Support for list elements

[pelletier197]

It would be great to have support of validation for list items.

For instance with this query schema

            type Query {
                cars(targets: [String!]! @NotBlank) : [Car]
            }

The @NotBlank could validate that every element of the list is not blank. This applies indeed for all the validations, except maybe for the expression, which could still be useful to use on a full list

[hantsy]

For a list, it should be @NotEmpty to check if there is an item in the collection.

[hantsy]

@NotBlank in bean validation is generally used to check if it is a empty string or a string only contained whitespace in the string.

[pelletier197]

Technically speaking, javax supports both collections and strings. https://javaee.github.io/javaee-spec/javadocs/javax/validation/constraints/NotEmpty.html. NotEmpty will allow whitespace characters, while NotBlank will ensure you have at least one non whitespace char.

But the way you can validate a list or the elements of a list with javax is as follow:

// list not empty 
public @NotEmpty List<String> field;

// strings in the list not empty
public List<@NotEmpty String> field;

The equivalent syntax does not compile in GraphQL.

// works 
field: [String] @NotEmpty

// does not work
field: [String @NotEmpty ]

Thus making it impossible to validate that strings are not empty and that lists are not empty at the same time. Same issue occurs with @Size.

In the linked MR, I came up with @ContainerNotEmpty and @ContainerSize to counter that issue. So far, I have got no news from the maintainers, but if you have a better idea to counter the issue, I'll be happy to change it.