Node.js : Day 13

CRUD operations in mongodb

CRUD operation In MongoDB:

What is CRUD?

→

C - CREATE

R - READ

U - UPDATE

D - DELETE

Q How to display a list of all databases that currently exist on the MongoDB server?

$ show databases

Exmaple:

C For Create

How to Create Database In mongoDB?

Syntax:

> use database_name

example: create a database for Smart_Phone.

Q. How to insert data in MongoDB?

→ By Insert Operation :

It will add new documents to a collection. If a collection does not exist, the insert operation will create one.

you can see there are no collections in the smart_phone database.

Let’s see, How to create a collection inside the database?

whenever we will insert something, that time only it will create a collection and insert documents into it.

Syntax for Insert operation :

> db.collection.insert( {           > db.collection.insertOne({
    field: value,            or           field: value,
    field: value                          field: value
 } )                                  } )

for example:

There are two ways to insert documents in collections:

1. By using insertOne():

→ db.collection.insertOne() command can be used to insert one document at a time.

2. By Using insertMany():

→ db.collection.insertMany() can be used for multiple documents insertion into the collection.

Q. How to Insert multiple documents?

→ by using an array([]).

Syntax :

> db.collection.insert( [    or   // db.collection.insertMany( [
  { document 1 },
  { document 2},
......
] )

example:

multiple documents insertion into the collection.

> db.product_catalog.insert([
 {
    prodid: 7000002,
    prodname: “iphone 8”,
    manufacturer: “apple”,
    categories: {main:”electronics”,sub:”smartphones”},
    date_of_launch: new Date(“2017–09–07”),
    price: 65000,
    colors: [“silver”,”black”,”gold”,”rosegold”]
 },
 {
    prodid: 7000003,
    prodname: “iphone 9”,
    manufacturer: “apple”,
    categories: {main:”electronics”,sub:”smartphones”},
    date_of_launch: new Date(“2018–09–07”),
    price: 70000,
    colors: [“silver”,”black”,”gold”,”rosegold”]
 }
])

1st example :

2nd example :

> db.product_catalog.insert ( 
[
    {prodid:7000010,prodname:”nosql distilled”,publisher:”Addison-Wesley”,ISBN:1234567,price:400},
     {prodid:7000011,prodname:”big data: principles and best practices”,publisher:”Dreamtech”,price:700}
] 
)

Additional Methods for Inserts:

The following methods can also add new documents to a collection:

• db.collection.updateOne() when used with the upsert: true option.
• db.collection.updateMany() when used with the upsert: true option.
• db.collection.findAndModify() when used with the upsert: true option.
• db.collection.findOneAndUpdate() when used with the upsert: true option.
• db.collection.findOneAndReplace() when used with the upsert: true option.
• db.collection.bulkWrite().

we will discuss these methods later in this blog.

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R For Read :

Q. How to retrieve documents from the collection?

→ By using the find operation.

Syntax :

> db.collection.find(
     { query criteria },
     { projection criteria }
)

There are two versions of the find operation:

1. findOne(): only one of the best documents from the collection they will show you.

2. find(): It will show you many documents from the collection.

for example:

• Projection: Only view the fields which require.

Syntax :

> db.collection.find(
    { query criteria },
    { projection criteria }
)

1 --> to include that field
0 --> exclude the field(all the field except one)

NOTE: In projection, At a time you can include or exclude, you can’t do both operations in the same projection query. (except in case of _id: 0)

In simple ways, it means:

1. {<field 1> : 1, <field 2> : 1} → valid

2. {<field 1> : 0, <field 2> : 0} → valid

3. {<field 1> : 1, <field 2> : 1,_id:0} → valid (Exception)

4.{<field 1> : 1, <field 2> : 0} → Invalid

Retrieve the documents based on the criteria :

Q. How to Retrieve the documents having prodname as ‘iphone 8’?

→

>db.product_catalog.find(
     {prodname: "iphone 8"}
)

Q. How to Retrieve the documents that either does not contain colors field or null value for that field?

> db.product_catalog.find(
 { colors:null }
)

**** Using existence check:

> db.product_catalog.find(
 { colors: {"$exists":true} }
)

if colors exists then it will retrieve documents otherwise it won’t retrieve documents.

Q. How to retrieve embedded documents?

→ embedded document means document inside the document.

example :

using . (dot) :

> db.product_catalog.find(
 { “categories.main”:”electronics” }
)

— — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —

U FOR Update :

Update operation allows users to modify the existing documents in a collection whenever a change occurs. A criteria or filter needs to be specified.

Syntax For updating documents :

MongoDB provides the following methods for updating documents in a collection:

1 . db.collection.updateOne():Updates at most a single document that matches a specified filter even though multiple documents may match the specified filter.

2. db.collection.updateMany():Update all documents that match a specified filter.

3. db.collection.replaceOne():Replaces at most a single document that matches a specified filter even though multiple documents may match the specified filter.

Examples :

For this practical, I am creating new database names ecommerce and inserting document in it.

> use ecommerce

Now Inserting documents in products collection.

> db.products.insertMany( 
  [    
      {prodid:7000010,prodname:”nosql distilled”,publisher:”Addison-Wesley”,ISBN:1234567,price:400},
      {prodid:7000011,prodname:”big data: principles and best practices”,publisher:”Dreamtech”,price:700}
      { prodid: 7000001,prodname: "iphone 7",manufacturer:"apple",
              categories:{main:"electronics",sub:"smartphones"},
              date_of_launch: new Date("2016-09-07"),price: 60000,
             colors: ["silver","black","gold","rosegold"]}

{ prodid: 7000002,prodname: "iphone 8",manufacturer:"apple",
              categories:{main:"electronics",sub:"smartphones"},
              date_of_launch: new Date("2017-09-07"),price: 65000,
             colors: ["silver","black","gold","white"]}   ]
)

Update a single document based on the condition :

Update the prodname of a book from “nosql distilled” to “NoSQL distilled”.

> db.products.updateOne(
     { prodname : "nosql distilled" },
     { $set : { "name" : "NoSQL distilled" }}
)

You can check whether it updated or not.

*** It is not updated it is inserted because name field was not there previously.:

> db.products.find(
     { prodname : "nosql distilled" }
)

Now, I am updating again ‘name’ → “NoSQL distilled” to “NoSQL”

> db.products.updateOne(
     { prodname : "nosql distilled" },
     { $set : { "name" : "NoSQL" }}
)

no check again it’s updated now :

> db.products.find(
     { prodname : "nosql distilled" }
)

Update a Multiple Embedded document based on condition :

Q. Update sub of categories smart phone to mobile phone based on condition wherever manufacturer is apple.

> db.products.updateMany(
     { "manufacturer": "apple" },
     { $set : { "categories.sub" : "mobile phone" }}
)

You can check whether it updated or not. :

> db.products.find(
     { manufacturer : "apple" }
)

Replace a document based on a condition:

> db.products.replaceOne( { “name” : “NoSQL” }, {"name":"Nosql distilled"})

whole data is replaced, as you can see in the below document :

Now again, I am replacing this document with a normal document whatever it was in the beginning.

> db.products.replaceOne(
  {name: "Nosql distilled"},
  {prodid:7000010,prodname:”nosql distilled”,publisher:”Addison-Wesley”,ISBN:1234567,price:400} 
);

You can check again is it replaced back to normal or not :

> db.products.find(
     { prodname : "nosql distilled" }
)

Using upsert to update documents else insert :

The operation updates all the documents with price greater than ‘80000’ and manufacturer ‘apple’. If there are no documents matching the given criteria, a new document would be inserted.

> db.product_catalog.updateMany(
 { “price” : { $gt : 80000 }, “manufacturer” : “apple” },
 { $set: { “prodname” : “iphone 7 plus” } },
 { upsert: true } 
)

we can see in ecommerce database :

> db.products.find(
     { manufacturer : "apple" }
)

Field Update Operators :

1. $inc : Increments the value of the field by the specified amount.

example :

Q. Increase the price of the book with ISBN ‘1979891’ by 20:

Before Increasing price :

> db.products.find(
 { ISBN: 1234567}
)

After running the query value would be increased so let’s check :

> db.products.update(
 { ISBN: 1234567 },
 { $inc: { price: 20 } }
)

For decreasing the price of ISBN:1234567. we just need to put (-)minus symbol before the value.

> db.products.update(
 { ISBN: 1234567 },
 { $inc: { price: -20 } }
)

2. $max : Only updates the field if the specified value is greater than the existing field value.

3. $min : Only updates the field if the specified value is less than the existing field value.

example :

Update the price of the product with ISBN ‘1234567’ to ‘430’ if the given new value is greater than the current value:

> db.products.update(
 { ISBN: 1234567 },
 { $max: { price: 430 } }
)

similarly, you can use $min too.

4. $mul: Multiplies the value of the field by the specified amount.

Multiply the price of the product by ‘2’ of ISBN ‘1234567’ :

db.products.update(
 { ISBN: 1234567 },
 { $mul: { price: 2} }
)

before multiplication :

After multiplication:

5. $rename: Renames a field.

Rename the price field to ‘Rs’ of ISBN ‘1234567’:

> db.products.update(
 { ISBN: 1234567 },
 { $rename: { "price": "Rs"} }
)

Renaming back ‘Rs’ to ‘price’:

6. $unset: Removes the specified field from a document.

let’s remove the price from the document with ISBN ‘1234567’:

> db.products.update(
 { ISBN: 1234567 },
 { $unset: { "price": ""} }
)

7. Again you can set price by $set operator:

> db.products.update(
 { ISBN: 1234567 },
 { $set: { "price": 400} }
)

Array Update Operators :

• dataset for array operator :

> use student

then insert these documents to student database in students collection.

> db.students.insertMany( [ 
{ “_id” : 1, “grades” : [ 85, 80, 80 ] }, 
{ “_id” : 2, “grades” : [ 88, 90, 92 ] }, 
{ “_id” : 3, “grades” : [ 85, 100, 90 ] }
] )

1. $ : Acts as a placeholder to update the first element that matches the query condition.

Syntax :

{ "<array>.$" : value }

Example :

To update the first element whose value is 80 to 82 in the in the grades array, use the positional $ operator if you do not know the position of the element in the array:

> db.students.updateOne(
   { _id: 1, grades: 80 },
   { $set: { "grades.$" : 82 } }
)

Before :

After running the query :

if you want to change all 80 to 82 then use $[]operator. let's see an example in the next section.

2. $[]: Acts as a placeholder to update all elements in an array for the documents that match the query condition.

Syntax :

{ "<array>.$[]" : value }

Example :

• Set all values of _id:2 are 80 by using $[] operator.

> db.students.updateOne(
     { _id: 2 }, 
     { $set: { “grades.$[]” : 80 } } 
)

Q. To update the All the element whose value is 80 to 82 in the in the grades array, use the positional $[] operator if you do not know the position of the element in the array:

> db.students.updateOne(
   { _id: 1, grades: 80 },
   { $set: { "grades.$[]" : 82} }
)

3. $[<identifier>]: Acts as a placeholder to update all elements that match the arrayFilters condition for the documents that match the query condition.

Syntax:

> db.collection.updateMany(
 { <query conditions> },
 { <update operator>: { “<array>.$[<identifier>]” : value } },
 { arrayFilters: [ { <identifier>: <condition> } ] }
)

Q. To update all elements that are greater than or equal to 85 in the grades array, use the filtered positional operator $[<identifier>] with the arrayFilters.

> db.students.updateMany(
 { },
 { $set: { “grades.$[element]” : 100 } },
 { arrayFilters: [ { “element”: { $gte: 85} } ] }
)

*** In this operator if query is not satisfied(no such document found). then it will upsert the document.

4.$addToSet: Adds elements to an array only if they do not already exist in the set.

Syntax:

> { $addToSet: { <field1>: <value1>, … } }

Example : -

We will use ecommerce database and products collections:

>use ecommerce

then you can see, some of colors of iphone 7 is already exist in colors array field.

I am adding ‘pink’ in colors array field by using $addToSet operator.

> db.products.update({“prodname”: “iphone 7”},{$addToSet:{colors:’pink’}})

5. $pop: Removes the first or last item of an array.

Syntax:

> { $pop: { <field>: <-1 | 1>, … } }

-1 --> for first item of array.
 1 --> for last item of array.

example :

Removing First colors of iphone 7:

> db.products.update({“prodname”: “iphone 7”},{$pop:{colors:-1}})

Removing last colors of iphone 7.

> db.products.update({“prodname”: “iphone 7”},{$pop:{colors:1}})

6. $push: Adds an item to an array.

The $push operator appends a specified value to an array.

Syntax:

> { $push: { <field1>: <value1>, … } }

Example:

Appending ‘blue’ in colors of iphone 7:

> db.products.update({“prodname”: “iphone 7”},
{$push:{colors:"blue"}})

7. $pull: Removes all array elements that match a specified query.

Syntax:

> { $pull: { <field1>: <value|condition>, <field2>: <value|condition>, … } }

Example: -

Pulling “black” and “gold” from colors array of iphone 7:

> db.products.updateOne( { “prodname”: “iphone 7”}, { $pull: { colors: { $in: [ "black", "gold" ] } } })

8. $pullAll: Removes all matching values from an array.

The $pullAll operator removes all instances of the specified values from an existing array. Unlike the $pull operator that removes elements by specifying a query, $pullAll removes elements that match the listed values.

Syntax:

>{ $pullAll: { <field1>: [ <value1>, <value2> … ], … } }

Example:

> db.products.update( { “prodname”: “iphone 7”}, { $pullAll: { colors: [ “blue”, “rosegold” ] } } })

D For Delete:

Delete Operation:

Delete operation allows you to delete the documents from a collection that is no longer valid. You can specify criteria or filters to delete documents.

• MongoDB provides following methods for delete document :

1. db.collection.deleteOne(): Delete at most a single document that match a specified filter even though multiple documents may match the specified filter.

Example:

Delete Only One Document that Matches a Condition :

• for this operation, we will using ecommerce database and products collection.

> use ecommerce

you can see products collection have this much documents.

> db.products.find({})

Q. Delete a document from products collection where “prodname” is “iphone 7”.

> db.products.deleteOne({prodname:iphone7})

After deleting document, you can see the collection again, it’s deleted.

2. db.collection.deleteMany(): Delete all documents that match a specified filter.

example:

Delete All Documents that Match a Condition:

Q. Delete a document from products collection where “manufacturer” is “apple”.

> db.produts.deleteMany({"manufacturer":"apple"})

let’s see this practically:

before the collection was like that.

After deleting the all the document where “manufacturer” is
“apple”.

> db.produts.deleteMany({"manufacturer":"apple"})

Delete All Documents:

• To delete all documents from a collection, pass an empty filter document {} to the db.collection.deleteMany() method.

> db.products.deleteMany({})

3. db.collection.remove(): Delete a single document or all documents that match a specified filter.

Normal Syntax:

> db.collection.remove( <query>, <justOne>)

Syntax:

> db.collection.remove( <query>, 
{ justOne: <boolean>,
 writeConcern: <document>, 
 collation: <document>, 
 let: <document> // Added in MongoDB 5.0 
}

• Delete a single document from collection with matching query :

> db.collection.remove( <query>, true )

• Delete all the document from collection with matching query:

> db.collection.remove( <query>)

• Delete all the document from collection:

> db.collection.remove({})

IF you want to know more about operators then you can read this blog.

Thank you…