CODEWITHSUNDEEP
node.jsmongodb
Himmators
Himmators

Reputation: 15006

When should I close this database connection?

I'm writing a script to modify all entries in a database. Here is a start to log them all.

 MongoClient = require('mongodb').MongoClient.connect("mongodb://localhost:27017/mydb", { useNewUrlParser: true } ),

(async () =>{
    let client;
    try {
        client = await MongoClient;
        let collection = client.db("booliscraper").collection("sold");
        let docs = await collection.find();
        docs.forEach((doc) => { 
            console.log(doc);
        })

  } catch(err) {
    log(err)
  }
})();

This works fine, but I want to close the db-connection somehow. I tried closing it outsidthe try/catch, but that seems to close the connection before all items are itterated through. Don't understand why.

...
  } catch(err) {
    log(err)
  }
  client.close();
})();

Upvotes: 0

Views: 70

Answers (2)

Afraz Ahmad
Afraz Ahmad

Reputation: 416

You can add finally block and close MongoDB connection there 

(async () => {
let client;
try {
    client = await MongoClient;
    let collection = client.db("booliscraper").collection("sold");
    let docs = await collection.find();
    await docs.forEach((doc) => {
        console.log(doc);
    })

} catch (err) {
    log(err)
} finally {
    client.close()
}})();

Here is reference try...catch

Upvotes: 0

Azami
Azami

Reputation: 2161

docs, the result of <Collection>.find(), is a cursor; and <Cursor>.forEach() is an async function.

Meaning your client.close() effectively gets called before you finished iterating over the cursor.

You may pass a second callback to forEach, that gets executed once the cursor has been exhausted:

MongoClient = require('mongodb').MongoClient.connect("mongodb://localhost:27017/mydb", { useNewUrlParser: true } ),

(async () =>{
    let client;
    try {
        client = await MongoClient;
        let collection = client.db("booliscraper").collection("sold");
        let docs = await collection.find();
        docs.forEach((doc) => { 
            console.log(doc);
        }, () => {
            //cursor is exhausted, close connection
            client.close();
        })

  } catch(err) {
    log(err)
  }
})();

For more information, this is documented in the Node.js Mongo DB Driver API.

Upvotes: 2

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