Single and list of data auto-handling

[DenisFerrero]

Hi, in my projects I handle many params as an array and they can be passed as a single value or as a list of values, but every time I have to manage this case manually

For example:

const Validator = require("fastest-validator");

const schema = {
    name: { type: 'multi', rules: [{ type: 'string' }, { type: 'array', items: 'string' }] }
};

const check = (new Validator()).compile(schema);

const params = { name: 'John' }

check(params);
if (params.name && !Array.isArray(params.name)) params.name = [params.name];

const query = `SELECT * FROM users WHERE name IN (${params.name.join(', ')})`

It would be great if this array conversion could be done directly by the validator using a parameter. For example:

const Validator = require("fastest-validator");

// By running an array validation with the wrap: true property the param even if it's a string it's wrapped inside an array before running the validation
const schema = {
    name: { type: 'array', items: 'string', wrap: true }
};

const check = (new Validator()).compile(schema);

const params = { name: 'John' }

check(params);
// params.name now is equal to ['John']

const query = `SELECT * FROM users WHERE name IN (${params.name.map(name => `'${name}'`).join(', ')})`

[erfanium]

I think that's out of scope. even TypeScript doesn't have support for it

[DenisFerrero]

Why not? Take for example using the validator for API requests' params, in some API standards to pass data in array format you have to repeat the parameter for each value
For example:

req.url = 'my-api.com?users=John&users=Jack'
req.query = { users: ['John', 'Jack'] }

If I want to pass just a parameter but still handle it as an array I have to change standard parameter handling because with the previous standard will result in this

req.url = 'my-api.com?users=John'
req.query = { users: 'John' }

and not into this

req.url = 'my-api.com?users=John'
req.query = { users: ['John'] }

I think that could be really useful in those cases

[erfanium]

I know it's useful but it can't be done at validation layer. it has some technical issues. e.g. how should we handle nested arrays? this logic only works for simple arrays like string[] and not for something like string[][]

you can achieve this behavior by using a pre-validation middleware. (or maybe by customizing this url queryparams parser)

[DenisFerrero]

Ok, that's right some cases can't be covered. Is there a way to add this property wrap: true with the related behavior into the validator using plugins? Even if it's out of scope it will be really useful at least to have it in my projects. There are aliases but I prefer to don't use them as the schemas are used by an external package to compile the Swagger automatically before the compilation.
Otherwise, I can also do this but it limits the usage of the custom methods of the validator in case of an array

function wrapFn (value) {
   if (value && !Array.isArray(value)) value = [value];
   return value;
}

const schema1 = {
   users: { type: 'array', items: 'string', custom: wrapFn }
}
const schema2 = {
   auths: { type: 'array', items: 'number', custom: wrapFn }
}

[icebob]

The convert option does the same for primitive types to convert string to number or date. Maybe we can do it for arrays, so if the input is not an array, it wraps the input into an array.

[DenisFerrero]

That would be great, so in the case of string[][] it's not considered an improper validation as it's just a data conversion process

[icebob]

Yeah, it just a helper to make an array wrapping. Could you create a PR?

[DenisFerrero]

Created a PR (#314) with the changes, updated tests (both JS and TS), and updated README

[DenisFerrero]

Closing issue as the changes have been merged