MongoDB - Delete Documents

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In this MongoDB tutorial we will learn to delete documents.

Login to your MongoDB server and insert the following documents.

For this tutorial I will insert the documents in the subscription collection.

> db.subscription.insertMany([
  {
    "firstname": "John",
    "lastname": "Doe",
    "uid": 1,
    "accountstatus": "ACTIVE",
    "plan": "TRIAL15DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Jane",
    "lastname": "Doe",
    "uid": 2,
    "accountstatus": "ACTIVE",
    "plan": "PLAN30DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Jim",
    "lastname": "Doe",
    "uid": 3,
    "accountstatus": "SUSPENDED",
    "plan": "PLAN60DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Alice",
    "lastname": "Doe",
    "uid": 4,
    "accountstatus": "ACTIVE",
    "plan": "PLAN1YEAR",
    "modifiedAt": null,
    "createdAt": new Date()
  }
])

Note! We are using new Date() to set the createdAt to current date time.

Delete one document

We use the deleteOne method to delete one document from a given collection.

In the following example we are deleting document having uid equal to 4.

> db.subscription.deleteOne({ "uid": 4 })

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MongoDB - Update Documents

Click the link: "MongoDB - Update Documents"

In this MongoDB tutorial we will learn to update documents.

Login to your MongoDB server and insert the following documents.

For this tutorial I will insert the documents in the subscription collection.

> db.subscription.insertMany([
  {
    "firstname": "John",
    "lastname": "Doe",
    "uid": 1,
    "accountstatus": "ACTIVE",
    "plan": "TRIAL15DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Jane",
    "lastname": "Doe",
    "uid": 2,
    "accountstatus": "ACTIVE",
    "plan": "PLAN30DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Jim",
    "lastname": "Doe",
    "uid": 3,
    "accountstatus": "SUSPENDED",
    "plan": "PLAN60DAYS",
    "modifiedAt": null,
    "createdAt": new Date()
  },
  {
    "firstname": "Alice",
    "lastname": "Doe",
    "uid": 4,
    "accountstatus": "ACTIVE",
    "plan": "PLAN1YEAR",
    "modifiedAt": null,
    "createdAt": new Date()
  }
])

Note! We are using new Date() to set the createdAt to current date time.

Update one document

To update a single document we use updateOne method.

Syntax

db.collectionName.updateOne(filter, update)

Where, filter is the condition to get the required document and update is the part of the document we want to update.

In the following example we are updating the account status of user having uid equal to 3 from SUSPENDED to ACTIVE.

> db.subscription.updateOne(
  { "uid": 3 },
  {
    $set: { "accountstatus": "ACTIVE" },
    $currentDate: { "modifiedAt": true }
  }
)

We use $set operator to update the value of accountstatus.

We use $currentDate operator to set the modifiedAt to current date.

If we now fetch the above document we will get the following.

> db.subscription.find({ "uid": 3 }).pretty()

{
  "_id" : ObjectId("5d7715d5b385796f53d4c8ff"),
  "firstname" : "Jim",
  "lastname" : "Doe",
  "uid" : 3,
  "accountstatus" : "ACTIVE",
  "plan" : "PLAN60DAYS",
  "modifiedAt" : ISODate("2019-09-10T03:18:42.406Z"),
  "createdAt" : ISODate("2019-09-10T03:17:41.130Z")
}

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MongoDB - Query for Null and Missing fields

Click the link: "MongoDB - Query for Null and Missing fields"

In this MongoDB tutorial we will learn to query for Null and missing fields.

Login to your MongoDB server and insert the following documents.

For this tutorial I will insert the documents in the deliveryAddress collection.

> db.deliveryAddress.insertMany([
  {
    "addressLine1": "House #1, 2nd Street, 1st Main Road",
    "addressLine2": "Opposite Bakery",
    "city": "Bangalore",
    "state": "KA",
    "country": "India",
    "pincode": "560001",
    "contactphone": "919800000000",
    "contactperson": "John Doe"
  },
  {
    "addressLine1": "House #20, 3rd Street, 5th Main Road",
    "addressLine2": null,
    "city": "Bangalore",
    "state": "KA",
    "country": "India",
    "pincode": "560001",
    "contactperson": "Jane Doe"
  },
  {
    "addressLine1": "House #20, 5th Street, 10th Main Road",
    "addressLine2": null,
    "city": "Bangalore",
    "state": "KA",
    "country": "India",
    "pincode": "560001",
    "contactphone": null,
    "contactperson": "Jim Doe"
  }
])

Select all documents having null field

In the following example we are fetching all the documents that have addressLine2 field set to null value.

> db.deliveryAddress.find({ "addressLine2": null }).pretty()


{
  "_id" : ObjectId("5d76170f89ccf6fae0c7974b"),
  "addressLine1" : "House #20, 3rd Street, 5th Main Road",
  "addressLine2" : null,
  "city" : "Bangalore",
  "state" : "KA",
  "country" : "India",
  "pincode" : "560001",
  "contactperson" : "Jane Doe"
}
{
  "_id" : ObjectId("5d76170f89ccf6fae0c7974c"),
  "addressLine1" : "House #20, 5th Street, 10th Main Road",
  "addressLine2" : null,
  "city" : "Bangalore",
  "state" : "KA",
  "country" : "India",
  "pincode" : "560001",
  "contactphone" : null,
  "contactperson" : "Jim Doe"
}

The $exists operator

To check if a document does or does not contains a given field we use the $exists operator.

Syntax

We use the following syntax to fetch all the documents of a given collection that does contains a given field.

db.collectionName.find({ field: { $exists: true } })

We use the following syntax to fetch all the documents of a given collection that does not contains a given field.

db.collectionName.find({ field: { $exists: false } })

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MongoDB - Query an Array of Embedded Documents

Click the link: "MongoDB - Query an Array of Embedded Documents"

In this MongoDB tutorial we will learn to query an array of embedded documents.

Login to your MongoDB server and insert the following documents.

For this tutorial I will insert the documents in the books collection.

> db.books.insertMany([
  {
    "title": "The C Programming Language",
    "author": ["Brian Kernighan", "Dennis Ritchie"],
    "inventory": [
      { "warehouse": "W1", "qty": 3000 },
      { "warehouse": "W2", "qty": 750 }
    ]
  },
  {
    "title": "MongoDB in Action",
    "author": ["Kyle Banker"],
    "inventory": [
      { "warehouse": "W2", "qty": 100 },
      { "warehouse": "W3", "qty": 1500 }
    ]
  },
  {
    "title": "Node.js in Action",
    "author": ["Marc Harter", "Nathan Rajlich", "T. J. Holowaychuk", "Mike Cantelon"],
    "inventory": [
      { "warehouse": "W1", "qty": 100 },
      { "warehouse": "W3", "qty": 250 }
    ]
  }

]);

Select based on exact match of embedded document in an array

In the following example we are fetching all the documents having the exact embedded document { "warehouse": "W1", "qty": 100 } in the inventory array.

Note! The field order is important i.e. the first field of the embedded document must be "warehouse" and must have value "W1" and the second field of the embedded document must be "qty" and must have value 100.

> db.books.find({ "inventory": { "warehouse": "W1", "qty": 100 } }).pretty();



{
  "_id" : ObjectId("5d2d9afd81a3cd0a9239c121"),
  "title" : "Node.js in Action",
  "author" : [
    "Marc Harter",
    "Nathan Rajlich",
    "T. J. Holowaychuk",
    "Mike Cantelon"
  ],
  "inventory" : [
    {
      "warehouse" : "W1",
      "qty" : 100
    },
    {
      "warehouse" : "W3",
      "qty" : 250
    }
  ]
}

If we change the field order of the embedded document in the query then we will not get the result.

In the following query we are changing the field order of the embedded document to { "qty": 100, "warehouse": "W1" } and it gives us no result.

> db.books.find({ "inventory": { "qty": 100, "warehouse": "W1" } }).pretty();

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MongoDB - Database and Collection

Click the link: "MongoDB - Database and Collection"

In this MongoDB tutorial we will learn about databases, collections and documents.

What is a document?

A document is a key value pair. It is a JSON (JavaScript Object Notation).

Following example represents a student document.

{
  "student_id": "s0001",
  "first_name": "Yusuf",
  "last_name": "Shakeel"
}

student_id, first_name and last_name are referred as the fields or keys of the document and s0001, Yusuf and Shakeel are the respective values of the given fields.

If you are familiar with RDBMS (eg. MySQL) then a MongoDB document is like a row in a RDBMS table.

What is a collection?

A collection is a set of documents.

A single collection can have zero or more number of documents.

Think of MongoDB collections as tables in RDBMS.

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