Iterate a Cursor in mongosh

Batch Sizes

A cursor returns documents in batches. By default, mongosh displays 20 documents per cursor iteration. You can use config.set("displayBatchSize") to change it, if this is too much or too little for your needs.

Insert Documents Into a New Collection

Use mongosh to insert documents into a new collection using the default test database:

db.users.insertMany( [
   { _id: 0, type: "admin", email: "admin@example.com", name: "Admin User" },
   { _id: 1, type: "user", email: "user1@example.com", name: "Test User 1" },
   { _id: 2, type: "user", email: "user2@example.com", name: "Test User 2" }
] )

Save a Cursor with let

In mongosh, the cursor does not automatically iterate when you assign it to a variable using the let keyword.

let myCursor = db.users.find( { type: "user" } )

You can call the cursor variable in the shell to print matching documents.

myCursor

[
   {
      _id: 1,
      type: 'user',
      email: 'user1@example.com',
      name: 'Test User 1'
   },
   {
      _id: 2,
      type: 'user',
      email: 'user2@example.com',
      name: 'Test User 2'
   }
]

If the returned cursor is not assigned to a variable using the let keyword, then the cursor is automatically iterated up to the batch size, printing the first batch of results.

db.users.find( { type: "user" } )

[
   {
      _id: 1,
      type: 'user',
      email: 'user1@example.com',
      name: 'Test User 1'
   },
   {
      _id: 2,
      type: 'user',
      email: 'user2@example.com',
      name: 'Test User 2'
   }
]

Access Documents in a Cursor with next()

You can also use the cursor method next() to access the documents. next() returns the document the cursor currently points and then moves the cursor forward to the next document.

let myCursor = db.users.find( { type: "user" } )
myCursor.next()

{
   _id: 1,
   type: 'user',
   email: 'user1@example.com',
   name: 'Test User 1'
}

Access Documents in a Cursor with hasNext()

The cursor method hasNext() returns true or false to indicate if there are more documents to be returned from the cursor.

let myCursor = db.users.find( { type: "user" } )
myCursor.hasNext()

true

You can use the hasNext() and next() methods to print all remaining documents from the cursor using the printjson() helper.

let myCursor = db.users.find( { type: "user" } )
while ( myCursor.hasNext() ) {
   printjson( myCursor.next() )
}

{
   _id: 1,
   type: 'user',
   email: 'user1@example.com',
   name: 'Test User 1'
}
{
   _id: 2,
   type: 'user',
   email: 'user2@example.com',
   name: 'Test User 2'
}

Access Documents in a Cursor with forEach()

Similarly, you can use the cursor method forEach() to apply a helper, such as printjson(), to each document in the cursor.

let myCursor = db.users.find( { type: "user" } )
myCursor.forEach( myDocument => printjson(myDocument) )

{
   _id: 1,
   type: 'user',
   email: 'user1@example.com',
   name: 'Test User 1'
}
{
   _id: 2,
   type: 'user',
   email: 'user2@example.com',
   name: 'Test User 2'
}

Starting in mongosh 2.1.0, you can also use for-of loops to iterate the cursor. The following example returns the same results as the previous example.

let myCursor = db.users.find( { type: "user" } )
for ( let myDocument of myCursor ) {
   printjson( myDocument )
}

{
   _id: 1,
   type: 'user',
   email: 'user1@example.com',
   name: 'Test User 1'
}
{
   _id: 2,
   type: 'user',
   email: 'user2@example.com',
   name: 'Test User 2'
}

See JavaScript cursor methods and your driver documentation for more information on cursor methods.

Access Documents in a Cursor with toArray()

In mongosh, use the toArray() method to iterate the cursor and return the documents in an array.

let myCursor = db.users.find( { type: "user" } )
let documentArray = myCursor.toArray()
documentArray

[
   {
      _id: 1,
      type: 'user',
      email: 'user1@example.com',
      name: 'Test User 1'
   },
   {
      _id: 2,
      type: 'user',
      email: 'user2@example.com',
      name: 'Test User 2'
   }
]

You can access the resulting document array as a traditional array.

let myCursor = db.users.find( { type: "user" } )
let documentArray = myCursor.toArray()
documentArray[1]

{
   _id: 2,
   type: 'user',
   email: 'user2@example.com',
   name: 'Test User 2'
}

The toArray() method loads all documents returned by the cursor into RAM and exhausts the cursor.

Some Drivers provide access to the documents by using an index on the cursor (i.e. cursor[index]). This is a shortcut for first calling the toArray() method and then using an index on the resulting array.

let myCursor = db.users.find( { type: "user" } )
myCursor.toArray() [1]

{
   _id: 2,
   type: 'user',
   email: 'user2@example.com',
   name: 'Test User 2'
}