I ma learning Prsima. And since I am not working in domain, stackoverflow is literally the only place where I can post some question that none of my actual colleagues/friends could answer.
I learned by some tutorials that we can query the database by simply initiate an instance and assign a result to a variable as the example bellow:
//initialise the db initiation
const user = prisma.user.find()... etc
However, on the documentation I find the following code:
const { PrismaClient } = require('#prisma/client')
const prisma = new PrismaClient()
async function main() {
// ... you will write your Prisma Client queries here
}
main()
.then(async () => {
await prisma.$disconnect()
})
.catch(async (e) => {
console.error(e)
await prisma.$disconnect()
process.exit(1)
})
They disconnect the database after each query. What is wrong with the first approach and what are the advantages of the second approach? I know that using plain mysql library in nodejs you must pay attention to the opened connections. But I don't understand prisma I want to learn to do the things right.
I assume the connection is never closed unless the NodeJS process is terminated (e.g. with CTRL + C), thus for small scripts where one single query is supposed to be executed it makes sense to then close the connection afterwards. For a long running server process it makes sense to just use one connection everywhere (or multiple if needed).
Related
I'm working on flutter app that uses php apis for server and sqlite for local data.
The problem is with "compute()".
Here is the explanation :
I have three functions that receives data from api on the server, then add the data to my local database (sqlite) table.
First function to get data from server.
Future<List<Map<String, dynamic>>> getServerData(int vers)async {
//my code
}
Second function to insert data into local database:
Future<int> addNewData(List<Map<String, dynamic>>)async {
//my code
}
Third function to call the first and second function:
Future<bool> checkServerData(int vers)async {
List<Map<String, dynamic>> sdt= await getServerData(vers);
int res=await addNewData(sdt);
if(res>0) return true;
else return false;
}
I want to call the third function in a compute function:
compute(checkServerData, 2);
When did that I found this error:
null check operator used on null value.
Note*:
If I used it without calling local database it works good.
The error appears if I called the database to insert data into.
When I searched about this issue I found that it's not allowed to access any resources which generated in one thread from another thread. But I didn't understand exactly how to resolve it or how to use another way that do the same idea.
After searching about the issue specified, I found those workaround solutions:
1: if the process is very important to work in background, you can use the Isolate package classes and functions which allow all isolated processes or contexts to share data between them as messages sending and receiving. But it's something complex for beginners in flutter and dart to understand these things, except those who know about threading in another environments.
To now more about that I will list here some links:
Those for flutter and pub documentation:
https://api.flutter.dev/flutter/dart-isolate/dart-isolate-library.html
https://api.flutter.dev/flutter/dart-isolate/Isolate-class.html
https://pub.dev/packages/flutter_isolate
This is an example in medium.com website:
https://medium.com/flutter-community/thread-and-isolate-with-flutter-30b9631137f3
2: the second solution if the process isn't important to work on background:
using the traditional approaches such as Future.builder or async/await.
You can know more about them here:
https://www.woolha.com/tutorials/flutter-using-futurebuilder-widget-examples
https://dart.dev/codelabs/async-await
and you can review this question and answers in When should I use a FutureBuilder?
I want to create a backend service which monitors a mongodb collection for new entries. As those are being created, I wish to run processing and update them.
I thought doing so with a Meteor service/app would be a wise idea because Meteor uses 'oplog tailing' which seems ideal for this purpose (I'd rather avoid polling if possible).
As such, I figured creating a minimal server-side-only app should solve it.
So basically, I need something along these lines:
if (Meteor.isServer) {
MyCollection = new Mongo.Collection('myCollection');
Meteor.publish('myCollectionPub', function () {
return MyCollection.find({ some: criteria... });
}
// is there such a thing?
Meteor.serverSideSubscribe('MyCollectionPub',
function (newDocs) {
// process/update newDocs
});
}
According to the Meteor docs, I cannot use Meteor.subscribe() on the server (and indeed it crashes if I try).
Question is:
Are there ways of 'subscribing' to collection updates on the server?
The PeerLibrary server-autorun package (along with it's dependant, reactive-mongo) will provide you with easy server-side observation of collections.
An alternative to #tarmes suggestion is the collection-hooks package, however as pointed out by David Weldon, it will only trigger in instance it is run in:
https://github.com/matb33/meteor-collection-hooks
MyCollection.after.insert(function (userId, doc) {
// ...
});
If you need it to run even when another instance makes a change in the mongo database, you can observe a cursor that is returned from your collection:
MyCollection.find({created_at : {$gt: some_current_time}}).observe({
added: function(item) {
// Alert code
}
});
I am a new user to JavaScript and the meteor framework trying to understand the basic concepts. First of all I want to add a single document to a collection without duplicate entries.
this.addRole = function(roleName){
console.log(MongoRoles.find({name: roleName}).count());
if(!MongoRoles.find({name: roleName}).count())
MongoRoles.insert({name: roleName});
}
This code is called on the server as well as on the client. The log message on the client tells me there are no entries in the collection. Even if I refresh the page several times.
On the server duplicate entries get entered into the collection. I don't know why. Probably I did not understand the key concept. Could someone point it out to me, please?
Edit-1:
No, autopublish and insecure are not installed anymore. But I already published the MongoRoles collection (server side) and subscribed to it (client side). Furthermore I created a allow rule for inserts (client side).
Edit-2:
Thanks a lot for showing me the meteor method way but I want to get the point doing it without server side only methods involved. Let us say for academic purposes. ;-)
Just wrote a small example:
Client:
Posts = new Mongo.Collection("posts");
Posts.insert({title: "title-1"});
console.log(Posts.find().count());
Server:
Posts = new Mongo.Collection("posts");
Meteor.publish(null, function () {
return Posts.find()
})
Posts.allow({
insert: function(){return true}
})
If I check the server database via 'meteor mongo' it tells me every insert of my client code is saved there.
The log on the client tells me '1 count' every time I refresh the page. But I expected both the same. What am I doing wrong?
Edit-3:
I am back on my original role example (sorry for that). Just thought I got the point but I am still clueless. If I check the variable 'roleCount', 0 is responded all the time. How can I load the correct value into my variable? What is the best way to check if a document exists before the insertion into a collection? Guess the .find() is asynchronous as well? If so, how can I do it synchronous? If I got it right I have to wait for the value (synchronous) because I really relay on it.
Shared environment (client and server):
Roles = new Mongo.Collection("jaqua_roles");
Roles.allow({
insert: function(){return true}
})
var Role = function(){
this.addRole = function(roleName){
var roleCount = Roles.find({name: roleName}).count();
console.log(roleCount);
if(roleCount === 0){
Roles.insert({name: roleName}, function(error, result){
try{
console.log("Success: " + result);
var roleCount = Roles.find({name: roleName}).count();
console.log(roleCount);
} catch(error){
}
});
}
};
this.deleteRole = function(){
};
}
role = new Role();
role.addRole('test-role');
Server only:
Meteor.publish(null, function () {
return Roles.find()
})
Meteor's insert/update/remove methods (client-side) are not a great idea to use. Too many potential security pitfalls, and it takes a lot of thought and time to really patch up any holes. Further reading here.
I'm also wondering where you're calling addRole from. Assuming it's being triggered from client-side only, I would do this:
Client-side Code:
this.addRole = function(roleName){
var roleCount = MongoRoles.find({name: roleName}).count();
console.log(roleCount);
if (roleCount === 0) {
Meteor.call('insertRole', roleName, function (error, result) {
if (error) {
// check error.error and error.reason (if I'm remembering right)
} else {
// Success!
}
});
}
}
How I've modified this code and why:
I made a roleCount variable so that you can avoid calling MongoRoles.find() twice like that, which is inefficient and consumes unneeded resources (CPU, disk I/O, etc). Store it once, then reference the variable instead, much better.
When checking numbers, try to avoid doing things like if (!count). Using if (count === 0) is clearer, and shows that you're referencing a number. Statements like if (!xyz) would make one think this is a boolean (true/false) value.
Always use === in JavaScript, unless you want to intentionally do a loose equality operation. Read more on this.
Always use open/closed curly braces for if and other blocks, even if it contains just a single line of code. This is just good practice so that if you decide to add another line later, you don't have to then wrap it in braces. Just a good practice thing.
Changed your database insert into a Meteor method (see below).
Side note: I've used JavaScript (ES5), but since you're new to JavaScript, I think you should jump right into ES6. ES is short for ECMAScript (which is what JS is based on). ES6 (or ECMAScript 2015) is the most recent stable version which includes all kinds of new awesomeness that JavaScript didn't previously have.
Server-side Code:
Meteor.method('insertRole', function (roleName) {
check(roleName, String);
try {
// Any security checks, such as logged-in user, validating roleName, etc
MongoRoles.insert({name: roleName});
} catch (error) {
// error handling. just throw an error from here and handle it on client
if (badThing) {
throw new Meteor.Error('bad-thing', 'A bad thing happened.');
}
}
});
Hope this helps. This is all off the top of my head with no testing at all. But it should give you a better idea of an improved structure when it comes to database operations.
Addressing your edits
Your code looks good, except a couple issues:
You're defining Posts twice, don't do that. Make a file, for example, /lib/collections/posts.js and put the declaration and instantiation of Mongo.Collection in there. Then it will be executed on both client and server.
Your console.log would probably return an error, or zero, because Posts.insert is asynchronous on the client side. Try the below instead:
.
Posts.insert({title: "title-1"}, function (error, result) {
console.log(Posts.find().count());
});
I'm a couple hours new to Meteor and Mongo, coming from a Rails background and trying to understand how migrations work - or don't maybe?
I have a server/bootstrap.js file that I use to seed some data:
// if the database is empty on server start, create some sample data.
Meteor.startup(function () {
if (Users.find().count() === 0) {
var userData = [
{ name: 'Cool guy' },
{ name: 'Other dude' }
];
for (var i = 0; userData.length; i++) {
var userId = Users.insert({
name: userData[i].name
});
}
}
});
It seems like every time I want to change the database, say to add a new field, I have to run meteor reset to get it to pick up the changes.
But what happens if I create records or other data through the UI that I want to keep? In Rails, working with MySQL or PostgreSQL, I'd create a migration to create new fields without blowing away the entire database.
How does this work with Meteor and Mongo? Also thinking of the case of rolling out new changes from development to production. Thanks!
-- Update: 2013/09/24 --
Apparently, the schema-less nature of Mongo reduces or eliminates the need for migrations. In my case, modifying userData to add new fields won't work after it runs initially because of the Users count check - which is why I kept running meteor reset. I'll need to rethink my approach here and study up.
That said, there are projects out there that use migrations, like Telescope: https://github.com/SachaG/Telescope/blob/master/server/migrations.js
I also found the tutorial at http://try.mongodb.org/ useful.
First of all, your code is perfectly valid. And you know that.
mrt reset gives you a 'fresh' - empty database (as mentionned already).
If you want to reset a particular collection, you can do it so :
MyCollection.remove({});
But you have to understand the nature of NoSQL : there are no constraints on the data. It could be called NoREL (as in not a relational database, source : Wikipedia ).
MongoDB is also schema-less.
This means that you can use any field you want in your data. This is up to you (the programmer) to enforce specific constraints if you want some. In other words, there is no logic on the mongo side. It should accept any data you throw at it, just like Hubert OG demonstrated. Your code snippet could be :
// if the database is empty on server start, create some sample data.
Meteor.startup(function () {
if (Users.find().count() === 0) {
var userData = [
{ name: 'Cool guy' },
{ name: 'Other dude' },
{ nickname: 'Yet another dude' } // this line shows that mongo takes what you throw him
];
for (var i = 0; userData.length; i++) {
var userId = Users.insert({
name: userData[i].name
});
}
}
});
Source : http://www.mongodb.com/nosql
There is no need for migration there. You only have to add the logic in your application code.
Note : To import/export a database, you can have a look there : mongo import/export doc, and maybe at the db.copyDatabase(origin, destination, hostname) function.
There are no migrations in Mongo — there is no scheme! If you want to add a new field that was not there before, just do it and it will work. You can even have completely different documents in the same collection!
Items.insert({name: "keyboard", type: "input", interface: "usb"});
Items.insert({cherries: true, count: 5, unit: "buckets", taste: "awesome"});
This will just work. One of main reasons to use NoSQL (and advantages of Meteor over Rails) is that you don't have migrations to worry about.
Using mrt reset to change db model is a terrible idea. What it actually does is complete reset of db — it removes all of your data! While it's sometimes usefull in development, I bet it's not what you want in this case.
I'm currently using the Zend_Db class to manage my database connections.
I had a few questions about it.
Does it manage opening connections smartly? (eg, I have a connection already open, does it know to take use of it - or do I have to constantly check if theres' already an open connection before I open a new one?)
I use the following code to fetch results (fetching in FETCH_OBJ mode):
$final = $result->fetchAll();
return $final[0]->first_name;
for some reason, fetchRow doesn't work - so I constantly use fetchAll, even when I'll only have one result (like searching WHERE id= number and id is a PK)
My question is - how much more time/memory am I sacrificing when I use fetchAll and not fetchRow, even when there's only result?
I've created the following class to manage my connections:
require 'Zend/Db.php';
class dbconnect extends Zend_Db
{
function init ()
{
$params = array (......
return Zend_Db::factory ( 'PDO_MYSQL', $params );
}
}
and then I call
$handle = dbconnect::init
$handle->select()....
is this the best way? does anyone have a better idea?
Thanks!
p.s. I'm sorry the code formatting came out sloppy here..
Lots of questions!
Does it manage opening connections
smartly?
Yes, when you run your first query, a connection is created, and subsequent queries use the same connection. This is true if you're reusing the same Zend_Db adapter. I usually make it available to my entire application using Zend_Registry:
$db = Zend_Db::factory(...) // create Db instance
Zend_Registry::set('db', $db);
//in another class or file somewhere
$db = Zend_Registry::get('db');
$db->query(...)//run a query
The above code usually goes in your application bootstrap. I wouldn't bother to extend the Zend_Db class just to initialise and instance of it.
Regarding fetchRow - I believe the key difference is that the query run is limited to 1 row, and the object returned is a Zend_Db_Table_Row rather than a Zend_Db_Table_Rowset (like an array of rows), and does not perform significantly slower.
fetchRow should be fine so post some code that's not working as there's probably a mistake somewhere.
addition to dcaunt's answer:
FetchAll returns array OR Zend_Db_Talbe_Rowset - depending on if you execute $zendDbTableModel->fetchAll() or $dbAdapter->fetchAll()
Same goes for fetchRow(). If you fail to make fetchRow working for models, it's easier to use $model->getAdapter()->fetchRow($sqlString);