# pouchdb

## Learning Path Diagrams Book Mode

[View on GitHub](https://github.com/apache/pouchdb "View on GitHub")

15 units • 5 levels

## Change Guide

Welcome to pouchdb

Your guide to understanding the codebase

### 5 levels

### 15 learning units

#### Orchestration & APIs
- Pipelines, workflows, public interfaces • 3 units

#### Document Operations & Data Model
- API·7

#### PouchDB Core Architecture
- Architecture·2

#### Essential Patterns & Utilities
- Patterns·4

#### Core Logic & Data
- Business rules, schemas, models • 3 units

#### Changes Feed & Query System
- API·7

#### Integration Layer
- Integration·12

#### Replication & Sync Protocol
- Workflow·6

#### Interaction & Integration
- UI components, external connectors • 2 units

#### Comprehensive Test Architecture
- Testing·5

#### Storage & Migration Systems
- Testing·7

#### Cross-Cutting Concerns
- Auth, logging, config, testing • 2 units

#### Advanced Concurrency & Documentation
- Concurrency·27

#### Performance & Reliability Testing
- Testing·15

#### Edge Cases & Resilience
- Error handling, fault tolerance • 2 units

#### Additional Data Model Patterns
- Data Model·2

#### Additional Error Handling Patterns
- Error Handling

## Test Your Knowledge

24 questions across all levels

### Progress 0/24 answered

#### Levels
- Level 1: 6
- Level 2: 6
- Level 3: 6
- Level 4: 6

## Hands-On Assignment

### 2-3 hours

### Your Challenge

Implement a document versioning plugin that maintains a complete history of document changes in a separate collection. When a document is updated or deleted, your plugin should automatically store the previous version in a `{dbname}_history` database with metadata about the change (timestamp, operation type, revision). This will allow developers to query historical versions and potentially restore previous states.

### Starting Points

- `CONTRIBUTING.md:1-72`
  Understand the project structure and how to set up your development environment for building and testing plugins

- `bin/build-module.js:1-66`
  Study how PouchDB modules are built and packaged - your plugin will follow similar patterns

- `bin/build-node.sh:1-7`
  See how the build process works for Node.js modules

### Success Criteria

- Plugin successfully intercepts put, post, and remove operations without breaking existing functionality
- Previous document versions are stored in a separate `{dbname}_history` database with proper metadata
- A `getHistory(docId)` method returns all historical versions of a document in chronological order
- A `restoreVersion(docId, timestamp)` method can restore a document to a previous state
- The plugin can be built using the existing build system (npm run build works)
- History entries include: original document content, revision, timestamp, and operation type
- Plugin handles edge cases: first document creation, missing history db, and deleted documents

### Hints

- **Hint 1:** Understanding PouchDB's plugin architecture conceptually
- **Hint 2:** Accessing document state before changes implementation
- **Hint 3:** Managing the history database implementation
- **Hint 4:** Plugin structure and API code location
- **Hint 5:** Handling edge cases conceptually

### Prerequisites

- JavaScript promises and async/await
- PouchDB basic operations (put, get, remove)
- Plugin architecture patterns
- Document revision system basics

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pouchdb - Learning Path