Connecting to the Database Instance

To initiate a session with the MongoDB server, open your system's command line interface (such as Terminal on Linux/macOS or Command Prompt on Windows). Execute the following commend to start the shell:

mongo

While working within the shell, you can clear the terminal output at any time to improve readability:

cls

Database and Collection Management

MongoDB operates on a lazy creation model; databases and collections are not fully created until data is written to them.

To switch to a specific database context (or create one if it does not exist), use the use command:

use inventory_db

To finalize the creation of the database, insert a document into a collection:

db.products.insert({"item": "notebook", "stock": 15});

To list all database currently present on the server:

show dbs;

To view the collections (analogous to tables in relational databases) within the current database:

show collections;

To permanently delete a specific collection:

db.products.drop();

To remove the entire database currently in context:

db.dropDatabase();

Inserting Documents

Data insertion into a collection can be performed using the insert method. The following example adds a new document with multiple fields:

db.products.insert({"item": "pen", "price": 1.50, "stock": 100});

Querying Data

MongoDB offers a robust querying syntax for retrieving data.

To retrieve all documents within a collection:

db.products.find();

To retrieve unique values for a specific field (e.g., finding all distinct item names):

db.products.distinct("item");

To find documents matching a specific criteria (e.g., stock equals 100):

db.products.find({"stock": 100});

Comparison Operators

Comparison operators allow for filtering based on numerical or logical conditions.

Find documents where stock is greater than 10:

db.products.find({stock: {$gt: 10}});

Find documents where stock is less than 50:

db.products.find({stock: {$lt: 50}});

Find documents where stock is greater than or equal to 20:

db.products.find({stock: {$gte: 20}});

Find documents where stock is less than or equal to 80:

db.products.find({stock: {$lte: 80}});

Find documents where price is between 5.00 and 10.00:

db.products.find({price: {$gte: 5.00, $lte: 10.00}});

Pattern Matching

Regular expressions can be used for text searching.

Find items where the name contains "pen":

db.products.find({item: /pen/});

Find items where the name starts with "note":

db.products.find({item: /^note/});

Find items where the name ends with "book":

db.products.find({item: /book$/});

Projection and Sorting

To query specific fields only (similar to SELECT item, price in SQL):

db.products.find({}, {item: 1, price: 1});

To sort results, use 1 for ascending order and -1 for descending order:

db.products.find().sort({price: 1});

Pagination and Logic

To implement pagination using limit and skip (e.g., retrieve 5 records starting after the first 10):

db.products.find().limit(5).skip(10);

To use an OR condition for queries (e.g., stock is 5 OR stock is 15):

db.products.find({$or: [{stock: 5}, {stock: 15}]});

To retrieve only the first matching document:

db.products.findOne();

To count the number of documents matching a filter (e.g., count items with price over 10):

db.products.find({price: {$gt: 10}}).count();

Modifying Data

Updates in MongoDB can target specific fields or replace entire documents.

To modify a specific field of a document (e.g., update the stock of "pen" to 50):

db.products.update({"item": "pen"}, {$set: {"stock": 50}});

By default, only the first matching document is updated. To update all matching documents, the multi option must be enabled:

db.products.update({"item": "pen"}, {$set: {"stock": 50}}, {multi: true});

To completely replace a document (excluding the $set operater), the entire content structure is provided:

db.products.update({"item": "pen"}, {"item": "fountain pen", "price": 5.00, "category": "luxury"});

To increment a numerical value (e.g., increase the price of "fountain pen" by 2):

db.products.update({item: 'fountain pen'}, {$inc: {price: 2}}, false, true);

You can combine operators, such as incrementing a value while setting another field simultaneously:

db.products.update({item: 'fountain pen'}, {$inc: {stock: 10}, $set: {status: 'restocked'}}, false, true);

Deleting Data

Removal of data can be selective or comprehensive.

To delete all documents matching a specific criteria (e.g., delete "luxury" category items):

db.products.remove({"category": "luxury"});

To ensure that only the first matching document is deleted, use the justOne flag:

db.products.remove({"category": "luxury"}, {justOne: true});