opt-cc/api/middleware/filter-handler-mongo.js

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2017-05-10 11:04:06 +02:00
/** This module defines a express.Router() instance
* - supporting filter=key1,key2
* - it sets res.locals.filter to a string "key1 key2"
* - calls next with error if a filter=key is given, but key does not exist (not raised on empty item arrays!)
*
* Note: it expects to be called before any data is fetched from DB
* Note: it sets an Error-Object to next with error.status set to HTTP status code 400
*
* @author Johannes Konert
* @licence CC BY-SA 4.0
*
* @module restapi/filter-middleware-mongo
* @type {Factory function returning an Router}
* @param Schema {Object} a MongooseSchema.path value or similar object with attributes representing the valid keys
* @param suppressId {Boolean} if true, the _id is not returned implicitly
*/
// remember: in modules you have 3 variables given by CommonJS
// 1.) require() function
// 2.) module.exports
// 3.) exports (which is module.exports)
"use strict";
const express = require('express');
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const logger = require('debug')('middleware:filterware');
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/**
* private helper function to filter Objects by given keys
* @param keys {Array} the keys from GET parameter filter
* @param schema [Object} containing the keys as attributes that are allowed
* @returns {Object or Error} either the filtered items or an Error object
*/
const limitFilterToSchema = (keys, schema) => {
if (!keys || !schema) { // empty arrays evaluate to false
return undefined; // means no filter at all
}
let error = null;
const result = [];
// now for each given filter=key1,key2in the array check that the schema allows this key and store it in result
keys.forEach((key) => {
if (schema.hasOwnProperty(key)) {
result.push(key);
} else {
error = new Error('given key for filter does not exist in ressource: ' + key);
}
});
return error ? error : result
};
/**
* closure function as factory returning the router
*
* @param Schema {Object} a MongooseSchema.path value or similar object with attributes representing the valid keys
* @param suppressId {Boolean} if true, the _id is not returned implicitly
* @returns {Router}
*/
const createFilterRouter = (schema, supressID) => {
const router = express.Router();
// the exported router with handler
router.use((req, res, next) => {
const filterString = req.query.filter;
let filterKeys = [];
let err = null;
if (filterString !== undefined) {
filterKeys = filterString.split(',');
filterKeys.forEach((item, index, array) => {
array[index] = item.trim();
});
filterKeys = filterKeys.filter((item) => {
return item.length > 0;
});
if (filterKeys.length === 0) {
err = new Error('given filter does not contain any keys');
err.status = 400;
} else {
const result = limitFilterToSchema(filterKeys, schema);
if (result instanceof Error) {
err = result;
err.status = 400;
} else {
res.locals.filter = result.join(' '); // create a string with space as seperator
if (supressID) {
res.locals.filter = '-_id ' + res.locals.filter;
}
}
}
}
if (err) {
logger(err);
next(err)
} else {
if (res.locals.filter) {
logger('Successfully set filter to ' + res.locals.filter);
}
next()
}
});
return router;
};
module.exports = createFilterRouter;