I want to compare two fields in my Waterline query in Sails.js application, e.g.: SELECT * FROM entity E WHERE E.current < E.max.
I've tried the following code, but it's expecting integer value to be passed to it instead of column name:
Entity.find({
where: {
current: {'<': 'max'}
}
});
So, how do I compare two columns?
I have ran some tests and at the same time read the Waterline documentation. There is no indication of anything that could possibly do comparison of two fields/columns via .find() or .where() methods. Reference: http://sailsjs.org/documentation/concepts/models-and-orm/query-language
Instead, I have used .query() method to compare two fields via SQL string such as :
Entity.query("SELECT * FROM `Entity` E WHERE E.current < E.max", function( err, res) {
if(err) {
//exception
} else {
console.log('response',res);
}
});
The other way would be to use one query to get the max before putting it in the criteria.
EntityOne.find({
sort: 'column DESC'
}).limit(1)
.exec(function(err,found){
var max = found[0]
EntityTwo.find({
where: {
current: {'<': found}
}
}).exec((err,found) {
// Do stuff here
});
});
The query method is ultimately going to be faster however
Related
how to filter record conditionally in prisma? For example, I have variable sortByYear that could contain either undefined or integer.
I just want to ask if there are any ways to refactor the implementation below. I have tried looking to their documentation but I can't find one.
let result = [];
if (sortByYear) {
result = await prisma.project.findMany({
where: { provider_id: 50 }
})
} else {
result = await prisma.project.findMany()
}
In laravel we can refactor this by using when clause that checks a variable first before executing the query. laravel when-clause
You can use a combination of spread syntax operation and ternary operation to accomplish this:
const result = await prisma.project.findMany({
where: {
...(sortByYear ? { provider_id: 50 } : {}),
},
});
Spread Syntax:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax
Conditional Ternary:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator
I'm trying to implement pagination with mongoose for a mongoDB collection.
The console.log(req.params.start); correctly outputs the start value. However, the query does not start at this value — it starts from the beginning, regardless of the value.
If I change req.params.start to a non variable number, 2, for example — it correctly skips 2 records.
sampleRoute.route('/collection/:start').get((req, res) => {
console.log(req.params.start);
MyModel.find()
.skip(req.params.start)
.limit(2)
.exec(function (err, doc) {
if(err) { res.status(500).json(err); return; };
res.status(200).json(doc);
});
})
How can I successfully skip using a variable? Thank you.
As req.params.start is passed as a string, I needed to convert it to Number:
.skip(Number(req.params.start))
I am using SailsJS on a project and I need to use native() for certain querys. The problem I have is that I can't find a proper way to instantiate a Waterline Model Object from the mongo collection find result. I have being searching information about this and the only thing I have found is the following:
var instance = new Model._model(mongo_result_item);
This should work properly, but when I do instance.save(function(err, ins){}); the model throws an error because of the "_id" field, that should be "id".
I have took a look into sails-mongo code and I found that for the "find" method they do this:
// Run Normal Query on collection
collection.find(where, query.select, queryOptions).toArray(function(err, docs) {
if(err) return cb(err);
cb(null, utils.normalizeResults(docs, self.schema));
});
So the normalizeResults does the magic with the "_id" attribute, and other stuff.
The way I am doing this right now is to require the sails-mongo utils.js file to have access to this method.
Full sample:
var mongoUtils = require('sails-mongo/lib/utils.js');
SampleModel.native(function(nativeErr, collection){
collection.find({ 'field' : value }).toArray(function(collectionErr, results){
if (!results || results.length == 0) return res.restfullInvalidFieldValue({ msg : 'INVALID_VALUE' });
var norm_results = mongoUtils.normalizeResults(results);
var instance = new SampleModel._model(norm_results[0]);
});
});
Is there a better / proper way to achieve this ?
I need to do a native search because I have found a problem with Waterline find() method using strings, where the search should be case sensitive. Every string field on the model is being used as a regular expression match of the form : /^{string}$/i
Searching by a regular expression with the case insensitive flag will give me problems. In the other hand, doing { field : { $regex : new RegExp('^'+regexp_escaped_string+'$') } } could be possible, but I think it will perform worst than { field : value }.
If someone have found a different workaround for the case insensitive problem, please, point me in the right direction.
Thanks in advance.
$regex might help you to search case insensitive string using option paramteter as "i", you can also specify custom regex instead for more information see $regex mongodb documentation.
/**
* PetController
*
* #description :: Server-side logic for managing pets
* #help :: See http://links.sailsjs.org/docs/controllers
*/
module.exports = {
searchByName: function (req,res) {
Pet
.native(function(err, collection) {
if (err) return res.serverError(err);
collection.find(
{
name: { $regex: /like-my-name/, $options: "i" } // here option "i" defines case insensitive
},
{
name: true
})
.toArray(function (err, results) {
if (err) return res.serverError(err);
return res.ok(results);
});
});
}
};
See here for more on native mongo query - https://stackoverflow.com/a/54830760/1828637
Ok, still in my toy app, I want to find out the average mileage on a group of car owners' odometers. This is pretty easy on the client but doesn't scale. Right? But on the server, I don't exactly see how to accomplish it.
Questions:
How do you implement something on the server then use it on the client?
How do you use the $avg aggregation function of mongo to leverage its optimized aggregation function?
Or alternatively to (2) how do you do a map/reduce on the server and make it available to the client?
The suggestion by #HubertOG was to use Meteor.call, which makes sense and I did this:
# Client side
Template.mileage.average_miles = ->
answer = null
Meteor.call "average_mileage", (error, result) ->
console.log "got average mileage result #{result}"
answer = result
console.log "but wait, answer = #{answer}"
answer
# Server side
Meteor.methods average_mileage: ->
console.log "server mileage called"
total = count = 0
r = Mileage.find({}).forEach (mileage) ->
total += mileage.mileage
count += 1
console.log "server about to return #{total / count}"
total / count
That would seem to work fine, but it doesn't because as near as I can tell Meteor.call is an asynchronous call and answer will always be a null return. Handling stuff on the server seems like a common enough use case that I must have just overlooked something. What would that be?
Thanks!
As of Meteor 0.6.5, the collection API doesn't support aggregation queries yet because there's no (straightforward) way to do live updates on them. However, you can still write them yourself, and make them available in a Meteor.publish, although the result will be static. In my opinion, doing it this way is still preferable because you can merge multiple aggregations and use the client-side collection API.
Meteor.publish("someAggregation", function (args) {
var sub = this;
// This works for Meteor 0.6.5
var db = MongoInternals.defaultRemoteCollectionDriver().mongo.db;
// Your arguments to Mongo's aggregation. Make these however you want.
var pipeline = [
{ $match: doSomethingWith(args) },
{ $group: {
_id: whatWeAreGroupingWith(args),
count: { $sum: 1 }
}}
];
db.collection("server_collection_name").aggregate(
pipeline,
// Need to wrap the callback so it gets called in a Fiber.
Meteor.bindEnvironment(
function(err, result) {
// Add each of the results to the subscription.
_.each(result, function(e) {
// Generate a random disposable id for aggregated documents
sub.added("client_collection_name", Random.id(), {
key: e._id.somethingOfInterest,
count: e.count
});
});
sub.ready();
},
function(error) {
Meteor._debug( "Error doing aggregation: " + error);
}
)
);
});
The above is an example grouping/count aggregation. Some things of note:
When you do this, you'll naturally be doing an aggregation on server_collection_name and pushing the results to a different collection called client_collection_name.
This subscription isn't going to be live, and will probably be updated whenever the arguments change, so we use a really simple loop that just pushes all the results out.
The results of the aggregation don't have Mongo ObjectIDs, so we generate some arbitrary ones of our own.
The callback to the aggregation needs to be wrapped in a Fiber. I use Meteor.bindEnvironment here but one can also use a Future for more low-level control.
If you start combining the results of publications like these, you'll need to carefully consider how the randomly generated ids impact the merge box. However, a straightforward implementation of this is just a standard database query, except it is more convenient to use with Meteor APIs client-side.
TL;DR version: Almost anytime you are pushing data out from the server, a publish is preferable to a method.
For more information about different ways to do aggregation, check out this post.
I did this with the 'aggregate' method. (ver 0.7.x)
if(Meteor.isServer){
Future = Npm.require('fibers/future');
Meteor.methods({
'aggregate' : function(param){
var fut = new Future();
MongoInternals.defaultRemoteCollectionDriver().mongo._getCollection(param.collection).aggregate(param.pipe,function(err, result){
fut.return(result);
});
return fut.wait();
}
,'test':function(param){
var _param = {
pipe : [
{ $unwind:'$data' },
{ $match:{
'data.y':"2031",
'data.m':'01',
'data.d':'01'
}},
{ $project : {
'_id':0
,'project_id' : "$project_id"
,'idx' : "$data.idx"
,'y' : '$data.y'
,'m' : '$data.m'
,'d' : '$data.d'
}}
],
collection:"yourCollection"
}
Meteor.call('aggregate',_param);
}
});
}
If you want reactivity, use Meteor.publish instead of Meteor.call. There's an example in the docs where they publish the number of messages in a given room (just above the documentation for this.userId), you should be able to do something similar.
You can use Meteor.methods for that.
// server
Meteor.methods({
average: function() {
...
return something;
},
});
// client
var _avg = { /* Create an object to store value and dependency */
dep: new Deps.Dependency();
};
Template.mileage.rendered = function() {
_avg.init = true;
};
Template.mileage.averageMiles = function() {
_avg.dep.depend(); /* Make the function rerun when _avg.dep is touched */
if(_avg.init) { /* Fetch the value from the server if not yet done */
_avg.init = false;
Meteor.call('average', function(error, result) {
_avg.val = result;
_avg.dep.changed(); /* Rerun the helper */
});
}
return _avg.val;
});
I have a number of records stored in a MongoDB I'm trying to output them to the browser window by way of a Node.JS http server. I think I'm a good portion of the way along but I'm missing a few little things that are keeping it from actually working.
The code below uses node-mongo-native to connect to the database.
If there is anyone around who can help me make those last few connections with working in node I'd really appreciate it. To be fair, I'm sure this is just the start.
var sys = require("sys");
var test = require("assert");
var http = require('http');
var Db = require('../lib/mongodb').Db,
Connection = require('../lib/mongodb').Connection,
Server = require('../lib/mongodb').Server,
//BSON = require('../lib/mongodb').BSONPure;
BSON = require('../lib/mongodb').BSONNative;
var host = process.env['MONGO_NODE_DRIVER_HOST'] != null ? process.env['MONGO_NODE_DRIVER_HOST'] : 'localhost';
var port = process.env['MONGO_NODE_DRIVER_PORT'] != null ? process.env['MONGO_NODE_DRIVER_PORT'] : Connection.DEFAULT_PORT;
sys.puts("Connecting to " + host + ":" + port);
function PutItem(err, item){
var result = "";
if(item != null) {
for (key in item) {
result += key + '=' + item[key];
}
}
// sys.puts(sys.inspect(item)) // debug output
return result;
}
function ReadTest(){
var db = new Db('mydb', new Server(host, port, {}), {native_parser:true});
var result = "";
db.open(function (err, db) {
db.collection('test', function(err, collection) {
collection.find(function (err, cursor){
cursor.each( function (err, item) {
result += PutItem(err, item);
});
});
});
});
return result;
}
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end("foo"+ReadTest());
}).listen(8124);
console.log('Server running on 8124');
Sources:
- mongo connectivity code:
https://github.com/christkv/node-mongodb-native/blob/master/examples/simple.js
- node. http code: nodejs.org
EDIT CORRECTED CODE
Thanks to Mic below who got me rolling in the right direction. For anyone interested, the corrected solution is here:
function ReadTest(res){
var db = new Db('mydb', new Server(host, port, {}), {native_parser:true});
var result = "";
res.write("in readtest\n");
db.open(function (err, db) {
res.write("now open\n");
db.collection('test', function(err, collection) {
res.write("in collection\n");
collection.find(function (err, cursor){
res.write("found\n");
cursor.each( function (err, item) {
res.write("now open\n");
var x = PutItem(err, item);
sys.puts(x);
res.write(x);
if (item == null) {
res.end('foo');
}
});
});
});
});
}
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.write("start\n");
ReadTest(res);
}).listen(8124);
console.log('Server running on 8124');
My guess is that you are returning result, writing the response, and closing the connection before anything is fetched from the db.
One solution would be to pass the response object to where you actually need it, something like:
function readTest(res) {
db.open(function (err, db) {
db.collection('test', function(err, collection) {
collection.find(function (err, cursor) {
res.writeHead(200, {'Content-type' : 'text/plain'});
cursor.each( function (err, item) { res.write(item); });
res.end();
...
Of course, you should also handle errors and try to avoid nesting too many levels, but that's a different discussion.
Instead of writing all the low-level Mongodb access code, you might want to try a simple library like mongous so that you can focus on your data, not on MongoDB quirks.
You might want to try mongoskin too.
Reading documents
To apply specific value filters, we can pass specific values to the find() command. Here is a SQL query:
SELECT * FROM Table1 WHERE name = 'ABC'
which is equivalent to the following in MongoDB (notice Collection1 for Table1):
db.Collection1.find({name: 'ABC'})
We can chain count() to get the number of results, pretty() to get a readable result. The results can be further narrowed by adding additional parameters:
db.Collection1.find({name: 'ABC', rollNo: 5})
It's important to notice that these filters are ANDed together, by default. To apply an OR filter, we need to use $or. These filters will be specified depending upon the structure of the document. Ex: for object attribute name for an object school, we need to specify filter like "school.name" = 'AUHS'
We're using here the DOT notation, by trying to access a nested field name of a field school. Also notice that the filters are quoted, without which we'll get syntax errors.
Equality matches on arrays can be performed:
on the entire arrays
based on any element
based on a specific element
more complex matches using operators
In the below query:
db.Collection1.find({name: ['ABC','XYZ']})
MongoDB is going to identify documents by an exact match to an array of one or more values. Now for these types of queries, the order of elements matters, meaning that we will only match documents that have ABC followed by XYZ and those are the only 2 elements of the array name
{name:["ABC","GHI","XYZ"]},
{name:["DEF","ABC","XYZ"]}
In the above document, let's say that we need to get all the documnts where ABC is the first element. So, we'll use the below filter:
db.Schools.find({'name.0': 'ABC' })