Assign value to a NodeJS variable with respect to MongoDB document array

Question

I have a MongoDB collection with the following documents

> db.mycol.find()
{ "_id" : ObjectId("5ec6506171ae442136aa97d2"), "uname" : "mail1", "port" : 1000, "abc" : "test1" }
{ "_id" : ObjectId("5ec659e6c0b1cc11370d8378"), "uname" : "mail2", "port" : 1001, "abc" : "test2" }

In the below code I am trying to fetch an array of document field port by making use of distinct in NodeJS.

var nextPort=0;
MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("mydb");
    dbo.collection("mycol").distinct('port', function(err, result) {
      if (err) throw err;
      console.log(result);
      db.close();
    });
  });

The above code gives an output [ 1000, 1001 ] Now, I have a variable called nextPort I want it to have the next value of already existing ports (should be unique and unused) i.e. if the last element of the array is 1001 then nextPort=1002.

How do I assign the next value (unique) from the array elements to my variable. Also is there a way to have all unique values in the document field port like we have primary key in MySQL

Stephan Du Toit · Accepted Answer · 2020-05-21 14:03:06Z

1

Not sure if this will help but you can try assigning the output to a variable, say "array". Then use nextPort = array[array.length-1]+1 See code sample below:

let nextPort=0; 
let arr = [1000, 1001];
nextPort = arr[arr.length-1]+1

or if you want to make nextPort an array:

let nextPort=[]; 
let arr = [1000, 1001];
nextPort.push(...arr, arr[arr.length-1]+1);

The code above assumes your Mongo code will always return a number.

answered May 21, 2020 at 14:03

Stephan Du Toit

8692 gold badges10 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

nomadev95 Over a year ago

I need your help with another thing. So basically I have a synchronous function (a child process) which makes use of nextPort and since it is a synchronous method it takes precedence over the function where I define the value of nextPort. Need a work around with that. As in the cp the nextPort value is set to 0. I have updated the code. Please have a look at it

nomadev95 Over a year ago

So what i want is - make the entire function synchronous MongoClient.connect(url, function(err, db)

Stephan Du Toit Over a year ago

mmm. Forgive my ignorance, but why would you want to make it synchronous as opposed to asynchronous? Is your goal to create / start multiple containers in parallel?

nomadev95 Over a year ago

Yes, I plan on creating multiple containers. And the MongoDB instance which I plan on provisioning takes port number as nextPort's value. As the child process in a sych function it takes precedence over the fucntion above (nextPort=0). This is the only reason I want the above function to take priority over execSync.

Stephan Du Toit Over a year ago

I have no idea. But I am fairly certain mongoconnect is asynchronous, which may actually be a good thing, it can ensure you never overwrite a port number or anything worse. Hope you come right. There are some super clever people here who I am sure can answer without much effort

Collectives™ on Stack Overflow

Assign value to a NodeJS variable with respect to MongoDB document array

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related