CODEWITHSUNDEEP
node.jsmongodbmonk
siva
siva

Reputation: 93

NodeJS/MongoDB: Perform Slice operation on an array field

I am having a tough time trying to execute a slice on an array I have a collection called comments, each document has an array field, i want to access it and apply slice for paging purpose please help !! tried monk and mongodb no good

Example:

 {  
   _id:xyz,
   msgs:[{.....},{.....},{.....}]
 }


database.collection("comments")
  .find({"_id": id},{ "msgs": { "$slice": [2,5] } })
  .toArray( function(err, result){
        //implementation
   });

Upvotes: 1

Views: 1283

Answers (2)

Tom Slabbaert
Tom Slabbaert

Reputation: 22276

From the node-js mongo driver docs:

2.x syntax:

const cursor = coll.find({ a: 42 }, { someField: 1 });

3.x syntax:

const cursor = coll.find({ a: 42 }).project({ someField: 1 });

/* OR */

`const cursor = coll.find({ a: 42 }, { projection: { someField: 1 } });`

Basically node-js mongo driver version upgrade from 2.x to 3.x had several "breaking" changes including the projection in a query.

Upvotes: 0

Koushik Shom Choudhury
Koushik Shom Choudhury

Reputation: 856

For mongodb Driver:

Instead of

.find({"_id": id},{ "msgs": { "$slice": [2,5] } })

Use

.find({"_id": id}).project({ "msgs": { "$slice": [2,5] } })

As given here the $slice operator is of Projection type. The mongodb driver for NodeJS needs call to an extra .project function to project selective fields as well as to use projection operators.

Upvotes: 6

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