How to Use WriteResult#getN() in MongoDB Java API for Efficient Write Operations

What is the purpose of the WriteResult#getN() method in the MongoDB Java API?

WriteResult result = collection.insertOne(doc);
int affectedCount = result.getInsertedCount(); // For insertions
int modifiedCount = result.getModifiedCount(); // For updates

The WriteResult#getN() method in the MongoDB Java API is used to retrieve the number of documents that were inserted, updated, or deleted as a result of a write operation. This method is essential for confirming the success and impact of database operations, allowing for error handling and validation processes in your application.

MongoCollection<Document> collection = database.getCollection("collectionName");

// Example of insertion
Document doc = new Document("name", "John Doe").append("age", 30);
WriteResult result = collection.insertOne(doc);

int numInserted = result.getInsertedCount(); // Retrieves the number of documents inserted
System.out.println(numInserted + " document(s) inserted.");

Causes

• This method counts the number of affected documents during write operations (insert, update, delete).
• It helps developers track changes and ensure data integrity.

Solutions

• Use WriteResult#getInsertedCount() to get the count of inserted documents
• Use WriteResult#getModifiedCount() to obtain the count of updated documents
• Implement error handling based on the count returned to ensure expected behavior.

Mistake: Not checking the return value of WriteResult#getN() after a write operation.

Solution: Always store and verify the results of the write operation to track the success and number of affected documents.

Mistake: Assuming WriteResult#getN() provides counts for all write operations.

Solution: Use the appropriate methods like getInsertedCount() for insertions and getModifiedCount() for updates.