w5 - mongoDB

Question 1

mongoDB

Answer 1

free document database management system that offers high scalability, availability, and flexibility

JSON-like documents, which means fields can vary from document to document, and data structure can be changed over time

Question 2

Document DB?

Answer 2

A record in MongoDB is a document, which is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents.

composed of field and value pairs

Question 3

difference between mongoDB and SQL?

Answer 3

SQL MongoDB
Database Database
Table Collection
Index Index
Row Document
Column Field

Question 4

Diff b/w mongoDB and JSON?

Answer 4

Compared to a JSON object, a MongoDB document has support for the primitive data types boolean, numbers, and strings and other common data types such as dates, timestamps, regular expressions, and binary data.

Question 5

MongoDB id?

Answer 5

A primary key is mandated in MongoDB and has the reserved field name _id.

Question 6

Benefits of compass MongoDB?

Answer 6

Visually explore your data.

Run ad hoc queries in seconds.

Interact with your data with full CRUD functionality

Question 7

MongoClient.connect(url, {useNewUrlParser: true}, function (err, client) {
if (err) {
console.log(‘Err ‘, err);
} else {
console.log(“Connected successfully to server”);
db = client.db(‘fi2095table’);
}
});

Answer 7

The first parameter is the server’s URL, which is a local server listening at port 27017 (MongoDB default port)

The second parameter is an object that is required for the latest version of MongoDB (version >4/0)

The third parameter is a callback function that will get executed after the connect operation finishes. It has two parameters: err object that gets value if an error occurs and client which is used later to access the database as shown in line 6 that connects to a database named ‘fit2095db

Question 8

Create

db.collection(‘week5table’).insertOne({name: ‘Tim’});

db.collection(‘week5table’).insertMany([
{ name: ‘Alex’, age: 25 },
{ name: ‘John’, age: 34 },
{ name: ‘Max’, age: 26 }
]);

Answer 8

The above statement references a collection named ‘week5table’. The statement creates the collection if it does not exist. Now, let’s insert a document that has one property {name:’Tim’}

insert multiple docs

Question 9

Read

findOne

find()

Answer 9

findOne-
returns one document that satisfies the specified query criteria on the collection. If multiple documents satisfy the query, this method returns the first document according to the natural order, which reflects the order of documents on the disk.

db.collection(“week5table”).findOne({ name: “Tim” }, function (err, result) {
console.log(result);
});

The find() method returns all occurrences in the selection.

db.collection(“week5table”).find({}).toArray(function (err, result) {
console.log(result);
});

Question 10

QUERY

Answer 10

To filter the result of the find() method, a query (i.e. criteria)object should be used.
let query = { name: ‘Alex’ };
db.collection(“week5table”).find(query).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 11

get all the documents where the name starts with ‘T’?

Answer 11

let query = { name: /^T/ };
db.collection(“week5table”).find(query).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 12

Finds all the documents where the name ends with ‘x’:

Answer 12

let query = { name: /x$/ };
db.collection(“week5table”).find(query).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 13

$gte
$lte

Answer 13

let query = { age: { $gte: 25 } };
db.collection(“week5table”).find(query).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 14

The list of Operators:

Answer 14

$currentDate Sets the value of a field to current date, either as a Date or a Timestamp.
$inc Increments the value of the field by the specified amount.
$min Only updates the field if the specified value is less than the existing field value.
$max Only updates the field if the specified value is greater than the existing field value.
$mul Multiplies the value of the field by the specified amount.
$rename Renames a field.
$set Sets the value of a field in a document.
$setOnInsert Sets the value of a field if an update results in an insert of a document. Has no effect on update operations that modify existing documents.
$unset Removes the specified field from a document.

Question 15

Sorting result?

Answer 15

The sort() method can be used to sort the result in ascending or descending order. The sort parameter contains field and value pairs in the following form:
{ field: value }

1-> ascending
-1->descending

Question 16

Sorting e.g?

Answer 16

let query = { age: { $gte: 25 } };
let sortBy={age:-1,name:1}
db.collection(“week5table”).find(query).sort(sortBy).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 17

Limit results?

Answer 17

We use the limit() method to limit the result in MongoDB. Example: return the top 5 documents that have age>=25.
let query = { age: { $gte: 25 } };
let sortBy = { age: -1 }
db.collection(“week5table”).find(query).sort(sortBy).limit(5).toArray(function (err, result) {
if (err) throw err;
console.log(result);
});

Question 18

DELETE

deleteOne

deleteMany

Answer 18

db.collection(“week5table”).deleteOne({ name: ‘Tim’ }, function (err, obj) {
console.log(obj.result);
});

db.collection(“week5table”).deleteMany({age: { $gte: 25 }}, function (err, obj) {
console.log(obj.result);
});

Question 19

UPDATE-

collection.updateOne()

Answer 19

collection.updateOne() updates a single document based on the filter.

Question 20

upset

Answer 20

option: a set of options to the update method such as upset that creates a new document if no documents match the filter. Example: update the age of a document with name=’Tim’ to be 31.
db.collection(“week5table”).updateOne({ name: ‘Tim’ }, { $set: {age: 31 } }, { upset: true }, function (err, result) {
});

db.collection(“week5table”).updateMany({ name: /x$/ }, { $inc: { age: 2 } }, { upsert: true }, function (err, result) {
});

Question 21

High availability?

Answer 21

MongoDB high availability is achieved by the replication facility, which is called replica set