Transforming input fields

I find myself short of an easy way to perform reusable transformation on input fields.

Say there is the following input object:

export const AddressInputType = new GraphQLInputObjectType({
    name: 'AddressInput',
    fields: () => ({
        name: {
            type: new GraphQLNonNull(GraphQLString),
        },
    }),
});

I would like to be able to do the following:

export const trim = (source, info) => source[info.fieldName].trim();
export const toUpperCase = (source, info) => source[info.fieldName].toUpperCase();

export const AddressInputType = new GraphQLInputObjectType({
    name: 'AddressInput',
    fields: () => ({
        name: {
            type: new GraphQLNonNull(GraphQLString),
            transform: [
                trim,
                toUpperCase,
            ],
        },
    }),
});

Returning undefined from a transform function should remove the field from the source object.

When to transform? I believe the transformation should occur after the type is parsed although arguments can be made to apply the transform before parsing. A potential solution is to have a transformBefore and a transformAfter property.

It should be possible to throw an error in the transform function. This should be handled similar to throwing an error in the type parser.

[MichalLytek]

For future readers - example here 😉 https://github.com/confuser/graphql-constraint-directive/blob/master/index.js

[MatthiasKunnen]

I checked out directives and while they don’t work the same as this proposal, they seem to be able to accomplish what I want. I’ll close this issue.