What is the type of ObjectId in MongoDB?

Makeup of an ObjectId This 12-byte configuration is smaller than a typical universally unique identifier (UUID), which is, typically, 128-bits. Beginning in MongoDB 3.4, an ObjectId consists of the following values: 4-byte value representing the seconds since the Unix epoch, 5-byte random value, and.

What are keys in MongoDB?

All documents in a MongoDB collection have a primary key dubbed _id . This field is automatically assigned to a document upon insert, so there’s rarely a need to provide it. What’s interesting about the _id field is that it is time based.

Which one is primary key in MongoDB?

In MongoDB, _id field as the primary key for the collection so that each document can be uniquely identified in the collection. The _id field contains a unique ObjectID value. When you query the documents in a collection, you can see the ObjectId for each document in the collection.

How ObjectId is created in MongoDB?

ObjectID is automatically generated by the database drivers, and will be assigned to the _id field of each document. ObjectID can be considered globally unique for all practical purposes. ObjectID encodes the timestamp of its creation time, which may be used for queries or to sort by creation time.

How replication works in MongoDB?

MongoDB achieves replication by the use of replica set. A replica set is a group of mongod instances that host the same data set. In a replica, one node is primary node that receives all write operations. All other instances, such as secondaries, apply operations from the primary so that they have the same data set.

What is key-value MongoDB?

Key-value stores are the simplest NoSQL databases. Every single item in a key value database is stored as an attribute name (or “key”) together with its value. Documents can contain many different key-value pairs, or key-array pairs, or even nested documents. MongoDB is a document database.

What is shard key in MongoDB?

The shard key is either a single indexed field or multiple fields covered by a compound index that determines the distribution of the collection’s documents among the cluster’s shards. Each range is associated with a chunk, and MongoDB attempts to distribute chunks evenly among the shards in the cluster.

What are the components of the ObjectId in MongoDB?

How Does MongoDB ObjectID Work?

• “a 4-byte value representing the seconds since the Unix epoch,
• a 3-byte machine identifier,
• a 2-byte process id, and a 3-byte counter, starting with a random value.”

What is the difference between MongoDB and RDBMS?

Examples of popular RDBMS are oracle, sql server, mysql etc. MongoDB is a NoSQL database. It is open source. It is a document oriented database and it uses BSON which is binary version of JSON. BSON is a document storage format.

Is it possible to convert primary keys to strings in MongoDB?

When you use primary keys as a sequential integer in MySQL or PostgreSQL, you put ints like 12345 you don’t put “12345” as a string. MongoDB cannot guess your use case since you don’t define a schema like you do in a RDBMS, don’t ask for auto conversion.

How do I use database commands in MongoDB?

To use database commands, see Issue Commands. A field required in every MongoDB document. The _id field must have a unique value. You can think of the _id field as the document’s primary key . If you create a new document without an _id field, MongoDB automatically creates the field and assigns a unique BSON ObjectId.

What is the _ID field in MongoDB?

A special virtual collection that exposes MongoDB’s database commands . To use database commands, see Issue Commands. A field required in every MongoDB document. The _id field must have a unique value. You can think of the _id field as the document’s primary key .