NoSQL Databases Guide

NoSQL Database Types

NoSQL databases are non-relational stores designed for specific data models. Four major types exist.

Document Databases (MongoDB)

Store data as JSON-like documents. Flexible schema, nested data:

db.users.insertOne({

name: "Alice",

email: "alice@example.com",

addresses: [{ city: "San Francisco" }]

});

Best for: flexible schemas, embedded data, rapid prototyping.

Key-Value Stores (Redis, DynamoDB)

Simple key-value pairs for fast lookups:

cache.set("user:123", json.dumps(user_data))

user = json.loads(cache.get("user:123"))

Best for: caching, session storage, simple lookups.

Wide-Column Stores (Cassandra, Bigtable)

Column-oriented with flexible schema per row key:

CREATE TABLE users (user_id UUID PRIMARY KEY, name TEXT, email TEXT);

Best for: time-series, write-heavy workloads, high scalability.

Graph Databases (Neo4j)

Nodes and edges representing entities and relationships:

MATCH (alice:Person)-[:FOLLOWS]->(friend)-[:PURCHASED]->(product)

RETURN product.name

Best for: social networks, recommendations, fraud detection.

Choosing a NoSQL Database

| Type | When to Use | Avoid For | |------|-------------|-----------| | Document | Flexible schemas | Complex joins | | Key-Value | Simple lookups | Multi-key queries | | Wide-Column | High-scale writes | Ad-hoc queries | | Graph | Connected data | Simple CRUD |

Conclusion

Match the NoSQL type to your data model. Document for nested data, key-value for caching, wide-column for scale, graph for relationships. Consider using multiple databases for different workloads.