salix/modules/client/models/client-sample.js

const UserError = require('vn-loopback/common/helpers').UserError;

module.exports = Self => {
    Self.validatesPresenceOf('typeFk', {
        message: 'Sample type cannot be blank'
    });

    Self.observe('before save', async function(ctx) {
        let models = Self.app.models;
        let data = ctx.instance;

        let sample = await models.Sample.findById(data.typeFk);

        if (sample.hasCompany && !data.companyFk)
            throw new UserError('Choose a company');

        let filter = {where: {userFk: ctx.options.accessToken.userId}};
        let worker = await Self.app.models.Worker.findOne(filter);

        data.workerFk = worker.id;
    });
};