CRUD Java

Question 1

True or False

BSON objects are more secure than JSON objects

Answer 1

True. BSON objects are not vulnerable to JSON injection attacks

Question 2

Which class does MongoDB recommend to represent BSON documents?

Answer 2

The Document class

Question 3

What is another name for “subdocument”?

Answer 3

Embedded document
Nested document

Question 4

Code an example of inserting a single document

Answer 4

collection.insertOne(new Document(field, value));

Question 5

Code an example of inserting multiple documents

Answer 5

var doc1 = new Document().append(field, value);
var doc2 = new Document().append(field, value);
List<Document> docs = Arrays.asList(doc1, doc2);
// List.of(...) also works
collection.insertMany(docs);

Question 6

Which factory class should you use for query documents?

Answer 6

The Filters class

Question 7

Code an example of finding one document in the database

Answer 7

collection.find(eq(field, value)).first();

Question 8

Code an example of obtaining and iterating through a cursor

Answer 8

try (var cursor = collection.find(eq(field, value)).cursor()) {
    while (cursor.hasNext()) {
        //...
    }
}

Question 9

True or False

An application should ensure that a cursor is closed in all circumstances, e.g. using a try-with-resources statement

Answer 9

True

Question 10

Which factory class should you use for update operators?

Answer 10

The Updates class

Question 11

Code an example of updating multiple fields in a single document

Answer 11

collection.updateOne(query, combine(set(field, value), set(field2, value2)));

Question 12

Code an example of inserting 2 documents to 2 different collections as a transaction

Answer 12

MongoClient client = MongoClients.create("...");
MongoCollection<Document> collection1 = client.getDatabase(name1).getCollection(name1);
MongoCollection<Document> collection2 = client.getDatabase(name2).getCollection(name2);

TransactionBody transaction = new TransactinBody<Void>() {
    public void execute() {
		    collection1.insertOne(clientSession, new Document(field, value));
				collection2.insertOne(clientSession, new Document(field, value));
}

try (ClientSession clientSession = client.startSession()) {
    clientSession.withTransaction(transaction);
}

Question 13

True or False

Transactions can only be used for write operations

Answer 13

False. Transactions can be used for both read and write operations

Question 14

True or False

Transactions are ACID compliant

Answer 14

True

Question 15

True or False

By default, MongoDB will cancel any transaction that runs for more than 80 seconds

Answer 15

False. Its 60 seconds

Question 16

Code an example of replacing a document and insert set to true

Answer 16

collection.replaceOne(eq(field, value), new Document(field, value), new ReplaceOptions().upsert(true));

Question 17

Code an example counting documents

Answer 17

collection.countDocuments(eq(field, value))

Question 18

Code an example limiting the number of documents found

Answer 18

collection.find().limit(number);

Question 19

Code an example of sorting documents in ascending order on multiple fields for a simple query

Answer 19

collection.find().sort(Sorts.ascending(field1, field2, ...))

Question 20

Code an example projecting multiple fields (include) and excluding the _id field for a simple query

Answer 20

collection.find().projection(Projections.fields(Projections.excludeId(), Projections.include(field1, field2)));

Question 21

Code an example updating a document with upsert set to true

Answer 21

collection.updateOne(Filters..., Updates.set(field, value), new UpdateOptions().upsert(true))