So, I have one collection called UserInfo that I use in different functions. Currently, I just create a local variable in every function that needs to use it. Is this normal practice? How expensive it is to create this collection variable?
ex: var collection = myDb.collection('UsersInfo');
I am assuming you are sharing myDB (mongoClient) across functions, probably passing them as function parameters or using globals.
If you have just one collection, why not do the same as myDb object with collection object.
Related
Recently I have decided to replace arrays with priority queues for storing my list of jobs for a user into MongoDB. I use NodeJS and ExpressJS for backend. The priority queue I attempted to store is from an external package which can be installed by running the following command in terminal:
yarn add js-priority-queue
For some reason the priority queue works perfectly prior to storing it into MongoDB. However, the next time I attempt to take it out of MongoDB and use it, its functionality is missing. I declare its type as Schema.Types.Mixed in the Schema. Am I doing something wrong or is it not possible to store instantiated class objects into MongoDB?
As far as I know, when you store things in MongoDB they are stored as extended JSON (EJSON) in binary format (BSON)
const { EJSON } = require('bson');
const test = EJSON.stringify({a: new Date(), foo:function(){console.log('foo');}})
console.log(test) // "{"a":{"$date":"2020-07-07T14:45:49.475Z"}}"
So any sort of function is lost.
I am working with SailsJs+MongoDB API. I have to create New colletion in mongoDB .Name of colletion will be in request Parameter.
example:
Suppose I want to create 'Users' collection in 'mongoDbDatabase' database
by following request.
{
"collectionName" : "Users",
"dbName" :"mongoDbDatabase"
}
Now is there any way to create dynamic collection in mongoDB using req.param('collectionName) variable ?
To use all the tools that Sails provides, you have to add code (before you start your app) for each Model / Collection you are planning to interact with. As a result, creating a collection dynamically will mean you can't take advantage of the whole data - framework sails provides.
Are you sure you need a dynamic collection? Why not a defined collection differentiated by attributes?
If you really need to do this from Sails, it looks like you can get access to the underlying raw mongo database:
var db = AnyModel.getDatastore().manager; // the database will be as defined in config/models.js or config/connections.js
var collectionName = 'Widgets';
db.createCollection(collectionName);
// note, even if this works, something like 'Widgets.find' will not.
I'm using MongoDB and Mongoose in a REST API. Some deployments require a replica set, thus separate read/write databases, so as a result I have separate read/write connections in the API. However, more simple deployments don't need a replica-set, and in those cases I point my read/write connections to the same MongoDB instance and database.
My general approach is to create all models for both connections at API start up. Even when read/write conns are connecting to same database, I am able to create the same models on both connections without error.
let ReadUser = dbRead.model('User', userSchema);
let WriteUser = dbWrite.model('User', userSchema);
// no error even when dbRead and dbWrite point to same DB
Trouble comes when until I start using Mongoose Discriminators.
let ReadSpecialUser = ReadUser.discriminator('SpecialUser', specialUserSchema);
let WriteSpecialUser = WriteUser.discriminator('SpecialUser', specialUserSchema);
// Results in this Error when read and write point to same DB:
// Error: Discriminator with name "SpecialUser" already exists
I'm look for an elegant way to deal with this. Is there a way to query the db for discriminators that are already in use?
According to the Mongoose API docs the way to do this is to use Model.discriminators. So in the case above it would be
ReadUser.discriminators
or
WriteUser.discriminators
However this doesn't return anything for me. What does work is using
Object.keys(Model.discriminators)
As expected this gets you an array of strings of the discriminator names you've set previously.
If you want to use the existing discriminator model and know its name what you can do is use Model.discriminators.discriminatorName. In your example it would be:
let ReadSpecialUserDocument = new ReadUser.discriminators.SpecialUser({
key: value,
key: value,
});
ReadSpecialUserDocument.save()
This can be useful when you need to reuse the discriminator at different times, and its name is tied to your data in some way.
So i have some variables, that contains strings. I would like to access my mongodb using these strings, but of course it won't work if i just write it down like that:
...some db connection code
var x="name";
...find all data, then loop
..function(err,docs){
docs[i].x;
}
The queastion is, how can i access the X parameters of my collection.
You can use this way :
database.mydata[i][x];
There are two different methods to obtain a reference to a MongoDB collection - both of them are used throughout the official documentation.
There is
var mycollection = db.collection('mycollection)'
and there is
db.collection('mycollection', function(err, collection){
//use collection
}
I tend to use the second one because it is consistent with "db.createCollecion(collection, callback)"
What is the difference between these methods?
Is there any database interaction when using these methods?
If you look at the code for Database, currently around line 456, you'll see that the only difference between the two in the way you've used them is how the collection object is returned. If you specify a callback, then it's returned that way, otherwise, it's returned as the value to the function. If you set the options however and specifically the option strict to true, you need to use the callback. When strict is set to true, the collection is verified before continuing (asynchronously).
Given that collections can be created dynamically (and usually are upon first use), there often isn't need to use strict mode.
So, it's really matter of personal coding preference otherwise. There is normally no activity to the database when creating a Collection object via: db.collection('collectionname') with the exception I mentioned above.