Introduction to MongoDB cursor.toArray() Method

In MongoDB, the cursor.toArray() method is used to return all documents returned by a cursor as an array. This method is executed on the server, so the number of documents returned and memory usage should be taken into consideration. If the result set is very large, it can cause the application to run out of memory.

Syntax

The syntax of the cursor.toArray() method is as follows:

db.collection.find().toArray()

Use Cases

The cursor.toArray() method can be used when all documents returned by a cursor need to be operated on as an array.

Note that this method can cause the application to run out of memory when used with large data sets. In such cases, it is recommended to use other methods to process documents one by one, or to use the cursor.batchSize() method to retrieve documents in batches.

Examples

Here are two examples of using the cursor.toArray() method:

Example 1

Assume we have a collection named users, which contains the following documents:

{ "_id": 1, "name": "Alice", "age": 25 }
{ "_id": 2, "name": "Bob", "age": 30 }
{ "_id": 3, "name": "Charlie", "age": 35 }

We can use the find() method to retrieve the cursor for all documents and use the toArray() method to return them as an array:

const cursor = db.collection("users").find()
const documents = cursor.toArray()

At this point, the documents array will contain all documents.

Example 2

Assume we have a collection named posts which contains a large number of documents. To avoid running out of memory in the application, we can use the batchSize() method to retrieve documents in batches and use the toArray() method to return them as an array.

const cursor = db.collection("posts").find().batchSize(100)
const documents = cursor.toArray()

At this point, the documents array will contain all documents, with 100 documents retrieved each time.

Conclusion

The cursor.toArray() method is used to return all documents returned by a cursor as an array. When using this method, the number of documents returned and memory usage should be taken into consideration. If the result set is very large, it can cause the application to run out of memory. In such cases, other methods can be used to process documents one by one, or the cursor.batchSize() method can be used to retrieve documents in batches.