MongoDB - CRUD | Knowledge Kitchen

# MongoDB CRUD

The dirty work of database data management.

---

# Agenda

1. [Overview](#overview)
1. [Servers](#servers)
1. [Clients](#clients)
1. [Example Data Set](#data-set)
1. [Create](#create)
1. [Operators](#operators)
1. [Read](#read)
1. [Update](#update)
1. [Delete](#delete)
1. [Conclusions](#conclusions)

---

# Overview

## Concept

MongoDB is a popular "document-oriented" database.

- MongoDB records are stored as Javascript Object Notation ([JSON](./plain-text-data-formats/#javascript-object-notation-json)) documents.

- commands and queries issued to the command-line MongoDB **client** program are written in Javascript.

- MongoDB integrates easily with popular programming languages, such as Javascript, Python, and others.

---

## Document-oriented database

MongoDB is not a relational database. It does not use the [SQL](/content/courses/database-design/slides/sqlite-intro) query language. It attempts to fill a need for document-centric databases that can scale up or down rapidly, as needed.

- no more tables, rows, or columns

- data are stored as "documents" in "collections"

- a database server can house many "collections"

- documents can contain the equivalent of primary and foreign keys

---

## No SQL

MongoDB is part of the "NoSQL" movement of databases that do not use SQL.

- MongoDB uses its own query language, based on Javascript

- many app or web programmers know Javascript, so this should make it more approachable

- [read more about the NoSQL trend](http://www.w3resource.com/mongodb/nosql.php) in database systems

---

## Flexible data model

Schema-less, meaning there is no fixed set of fields in any document

- Documents can have whatever fields you decide to store in them

- Even documents within the same collection can differ in their fields

---

## Cross-platform

MongoDB can run be "installed" and "setup" on all popular platforms, including Mac, Windows, Linux, and UNIX

- "Drivers" are available to be "installed" for most popular programming languages to allow them to communicate with MongoDB databases

---

## Highly scalable

Built-in ability to be "sharded"

- a single database can be split across many servers, or even many thousands of servers

- this allows MongoDB to potentially run thousands of times faster than if a database were on a single computer with limited processing and memory power

---

## Fast for large data sets

MongoDB is fast for large data sets

- includes sophisticated **indexes** to "pre-sort" results before queried

- supports many aggregate functions

---

## Geospatial search

MongoDB has built-in ability to store geospatial coordinates

- this means it can perform searches for documents "near me"

- easily performs searches within a particular radius of any location

- in other words, it can order results by how far they are from any geospatial location

---

## Industry-proven

MongoDB is used by:

- GitHub

- Etsy

- Google

- Ebay

- Expedia

- and [many more](https://www.mongodb.com/who-uses-mongodb)

Despite this MongoDB marketing, you can be sure that these organizations also use relational SQL databases aplenty.

---

## CRUD with the mongo shell client

The `mongosh` command line client (called `mongo` in older versions) uses a Javascript command shell interpreter to allow users to issue commands to any database to which they connect.

- as with databases of all kinds, most MongoDB commands engage in some form of CRUD

- *C*reate
    - *R*ead
    - *U*pdate
    - *D*elete

We will show how to do common CRUD operations using the `mongosh` client.

---

# Servers

## Overview

There are a variety of options for accessing a MongoDB server.

- cloud-based servers
- university servers
- personal hosted servers

---

## Cloud-based servers

[MongoDB Atlas](https://www.mongodb.com/cloud/atlas)

- cloud-based service that provides a free tier for small databases

---

## University servers

[NYU CIMS MongoDB server](https://cims.nyu.edu/webapps/content/systems/userservices/databases/class-mongodb)

- accessible to NYU students in courses related to databases.

---

## Local installation

[MongoDB Community Server](https://www.mongodb.com/download-center/community)

- a free, open-source server that can be installed on your own computer

---

## Local installation (continued)

[Docker image](https://hub.docker.com/_/mongo)

- Docker [containers](/content/courses/software-engineering/slides/containers) are small-footprint portable software environments
- [MongoDB](./mongodb-setup) maintains a Docker [container](/content/courses/software-engineering/slides/containers) image that can be used to run a MongoDB server locally in a container.

To use...

- install and run [docker desktop](https://www.docker.com/get-started)
- create a [dockerhub](https://hub.docker.com/signup) account
- run command, `docker run --name mongodb_dockerhub -p 27017:27017 -e MONGO_INITDB_ROOT_USERNAME=admin -e MONGO_INITDB_ROOT_PASSWORD=secret -d mongo:latest`
- connect to the database server from the command line: `docker exec -ti mongodb_dockerhub mongosh -u admin -p secret`
- show the available databases: `show dbs`
- select the database used by this app: `use your_db_name`... this will create a new database if one does not exist by that name
- exit the database shell whenever you have had your fill: `exit`

---

# Clients

## Overview

Connecting to a MongoDB server requires some sort of client program, typically either a shell program that you run locally.

---

## Mongo Shell

To access a MongoDB server from the command line, one needs to install [mongosh](https://www.mongodb.com/docs/mongodb-shell/).

- connect to a server: `mongosh your_database_name --host your_hostname -u your_username -p`.
- e.g. `mongosh example --host class-mongodb.cims.nyu.edu -u fb1258 -p`... after running this command, you will be asked for your password and then let in.

Note that if running a MongoDB server [within a local Docker container](#docker), you already have `mongosh` available within the container.

---

## MongoDB Database Tools

If connecting to a server from your local machine...

- install [mongosh](#mongosh)
- install `mongoimport` and other utilities in the [MongoDB Database Tools](https://www.mongodb.com/docs/database-tools/).

---

## Graphical User Interfaces

[MongoDB Compass](https://www.mongodb.com/products/compass)

- free GUI client for MongoDB by MongoDB

[Studio 3T](https://studio3t.com/free/)

- free GUI client for MongoDB

---

# Example Data Set

## Save the data file

This set of slides shows examples using a data set about books. To follow along, save the following JSON data into a file named [books.json](../assets/mongodb/books.json).

```javascript
{"title": "Northanger Abbey", "author": "Austen, Jane", "year_written": 1814, "edition": "Penguin", "price":  18.2}
{"title": "War and Peace", "author": "Tolstoy, Leo", "year_written": 1865, "edition": "Penguin", "price":  12.7}
{"title": "Anna Karenina", "author": "Tolstoy, Leo", "year_written": 1875, "edition": "Penguin", "price":  13.5}
{"title": "Mrs. Dalloway", "author": "Woolf, Virginia", "year_written": 1925, "edition": "Harcourt Brace", "price":  25}
{"title": "The Hours", "author": "Cunnningham, Michael", "year_written": 1999, "edition": "Harcourt Brace", "price":  12.35}
{"title": "Huckleberry Finn", "author": "Twain, Mark", "year_written": 1865, "edition": "Penguin", "price":  5.76}
{"title": "Bleak House", "author": "Dickens, Charles", "year_written": 1870, "edition": "Random House", "price":  5.75}
{"title": "Tom Sawyer", "author": "Twain, Mark", "year_written": 1862, "edition": "Random House", "price":  7.75}
{"title": "A Room of One's Own", "author": "Woolf, Virginia", "year_written": 1922, "edition": "Penguin", "price":  29}
{"title": "Harry Potter", "author": "Rowling, J.K.", "year_written": 2000, "edition": "Harcourt Brace", "price":  19.95}
{"title": "One Hundred Years of Solitude", "author": "Marquez", "year_written": 1967, "edition": "Harper  Perennial", "price":  14.00}
{"title": "Hamlet, Prince of Denmark", "author": "Shakespeare", "year_written": 1603, "edition": "Signet  Classics", "price":  7.95}
{"title": "Lord of the Rings", "author": "Tolkien, J.R.", "year_written": 1937, "edition": "Penguin", "price":  27.45}
```

---

## Saving the data file to a web server

If you typically connect to the MongoDB database server from a web server, such as **i6** , it's easy to upload the data file to the web server using a Secure File Transfer (SFTP) application like [Cyberduck](https://cyberduck.io/).

![Cyberduck login](../assets/mongodb/cyberduck.png)

---

## Import the data into MongoDB

To import the data file into a MongoDB database collection, go to the UNIX/Linux command line from where you typically connect to a MongoDB database, navigate to whichever folder you saved the data file into, and issue the following command:

- Note that this requires the `mongoimport` utility - see [installation instructions](https://www.mongodb.com/docs/database-tools/mongoimport/#installation) if the command is not found on your system.

```bash
mongoimport --db your_database_name --collection books --host database_host --username your_username --password your_password --type json --file books.json
```

- replace `database_host`, `your_database_name`, `your_username`, and `your_password` with the correct credentials.

- Note also that if running MongoDB within a Docker container, you may have to modify this command - [see discussion](https://stackoverflow.com/questions/49895447/i-want-to-execute-mongoimport-on-a-docker-container).

- MongoDB can import both [JSON and CSV plain text data formats](/content/courses/database-design/slides/plain-text-data-formats), although JSON is much more closely related to MongoDB's internal data structure and can be considered its native format.

- note that the `mongoimport` command is not run from within the `mongo` client.

---

## Connect to the database with the mongo shell client

Once the data has been imported, you can log in to the database server using the `mongosh` client (or `mongo` on older systems):

`mongosh your_database_name --host your_hostname -u your_username -p`

- replace `your_database_name` with your own NYU Net ID
- replace `your_hostname` with `class-mongodb.cims.nyu.edu`
- replace `your_username` with your own NYU Net ID
- you will be prompted to enter your MongoDB server password... do so... this is not the same as your i6 password

---

# Create

## Collections

There is no need to explicitly create a collection. Collections are created automatically as soon as the first document is saved into them.

---

## insert()

Documents can be created and stored into collections by importing from a JSON data file, as we have seen, or by using the `insert()` function.

```javascript
db.books.insert({
  title: "Pattern Recognition",
  author: "William Gibson",
  year_written: 2003,
  edition: "Penguin",
  price: 14.99,
})
```

- where `books` is a collection name that already exists or will be created automatically

---

# Read

## find()

The MongoDB `find()` function retrieves existing data from records in a given collection. It takes two arguments

- the **criteria** - that criteria that records must match to be included in the result set

- this acts much like SQL's `WHERE` clause

- the **projection** - limits which fields from the records matching the criteria will be included in the records in the result set
  - this acts much like the list of fields to retrieve in SQL's `SELECT` query

---

## Retrieve all documents

```javascript
db.books.find()
```

- where `books` is the collection from which to retrieve documents.

---

## One criterion

```javascript
db.books.find({
  author: "Tolstoy, Leo",
})
```

- retrieves all books where the `author` field has the value `Leo Tolstoy`

---

## One criterion with an operator

```javascript
db.books.find({
  price: {
    $gt: 25,
  },
})
```

- The `$gt` operator performs a "greater than" comparison.

---

## Two criteria

```javascript
db.books.find(
  {
    price: {
      $gte: 10,
      $lte: 20,
    },
    edition: "Penguin",
  },
  {
    _id: 0,
  }
)
```

Notes:

- **and** logic is implicit in the syntax of the price criteria
- the **projection** (the second argument) indicates to not include the `_id` field in the results.

---

## Two criteria

```javascript
db.books.find(
  {},
  {
    _id: 0,
    title: 1,
  }
)
```

Notes:

- This will return all book documents, since the **criteria** argument is a blank object.
- Only the `title` field will be included in the results for each document, since the **projection** argument indicates to do so.

---

## One criterion using the $or operator

```javascript
db.books.find({
  $or: [
    {
      price: {
        $gte: 20,
      },
    },
    {
      edition: "Penguin",
    },
  ],
})
```

Notes:

- **or** logic has to be explicitly indicated by the $or operator
- the syntax for the `$and` operator follows the same pattern

---

## Counting records

The `count()` function can be run on any query to count results.

```javascript
db.books
  .find({
    edition: "Penguin",
  })
  .count()
```

---

# Operators

## Comparisons

A variety of operators allow criteria to be fine-tuned.

- `$eq` - equal to
- `$ne` - not equal to
- `$gt` - greater than
- `$gte` - greater than or equal to
- `$lt` - less than
- `$lte` - less than or equal to

---

## Logic

Some other common operations have operators as well:

- `$and` - performs **and** logic
- `$or` - performs **or** logic
- `$in` - determines whether a value in a given field matches one of the values in an array
- `$nin` - determines whether a value in a given field does not match one of the values in an array

---

## Implicit equality

The following retrieval will match books where the `edition` field has exactly the value, "Penguin".

```javascript
db.books.find({
  edition: "Penguin",
})
```

- The equality operator is implicit.

---

## Implicit $eq

The same retrieval, in a more formal style, explicitly uses the `$eq` operator.

```javascript
db.books.find({
  edition: {
    $eq: "Penguin",
  },
})
```

- The equality `$eq` operator is explicit.

---

## Implicit and

As we've seen, MongoDB's default operator is the **and** operator.

```javascript
db.books.find({
  price: {
    $gte: 10,
    $lte: 20,
  },
  edition: "Penguin",
})
```

- There is no need to explicitly mention **and**.

- This will find books that match the `price` **and** the `edition` criteria

- The `price` criterion will match books that are greater than $10 **and** less than $20

- The `edition` criterion will match books that have exactly "Penguin" as their edition value.

---

## Explicit $and

The **and** logic in a query could be made more explicit. We can check a field in each documents against an array of criteria.

```javascript
db.books.find({
  $and: [
    {
      price: {
        $gte: 10,
      },
    },
    {
      price: {
        $lte: 20,
      },
    },
  ],
})
```

- This is quite a mouthful of `(`, `[`, `{`, `$`, `,`, `}`, `]`, and `)` characters.
- The implicit **and** seems nicer, when possible.

---

## Explicit $or

**or** logic is written in much the same way as the explicit `$and`.

```javascript
db.books.find({
  $or: [
    {
      author: "Gibson, William",
    },
    {
      author: "Tolstoy, Leo",
    },
  ],
})
```

---

## $in

If checking for a single field to have one of the values from a list of values, the `$in` operator can be less verbose than the explicit $or operator.

```javascript
db.books.find({
  author: {
    $in: ["Gibson, William", "Tolstoy, Leo"],
  },
})
```

---

## $nin

Check that a document's field value is not one of an array of values.

```javascript
db.books.find({
  year_written: {
    $nin: [1865, 1925, 1927, 1802, 1814, 1999],
  },
})
```

---

# Update

## update()

To update existing documents, use the `update()` method.

```javascript
db.books.update(
  { year_written: { $lt: 2000 } },
  { $set: { price: 5.99 } },
  { multi: true }
)
```

- the first argument specifies the criteria indicating which documents to update
- the second argument represents the fields to be changed and their new values
- the third argument indicates to apply this to all rows that match the criteria

---

# Delete

## remove()

To delete existing documents, use the `remove()` method.

```javascript
db.books.remove({
  author: "William Gibson",
  title: "Pattern Recognition",
})
```

- the argument sets the criteria that must be matched for any documents to be deleted

---

# Conclusions

Thank you. Bye.