# gupthamandavilli/employee_management architecture

> Architecture diagram of the GitHub repository gupthamandavilli/employee_management, generated by GitDiagram from its file tree, README and a sample of source files (last updated 2026-08-12). It is an AI-made overview: check details against the source.

- Interactive diagram: https://gitdiagram.com/gupthamandavilli/employee_management
- Repository: https://github.com/gupthamandavilli/employee_management

## Overview

#### Purpose and entry points
This is a full-stack employee-management CRUD system: an Angular 22 single-page client consumes an Express REST API, which persists employees to PostgreSQL when available and otherwise uses an in-memory store. Runtime entry points are `frontend/src/main.ts` for the browser app and `backend/server.js` for the API; root `package.json` coordinates separate frontend/backend commands.

#### Angular application shell and routing
Angular bootstraps standalone application configuration from `frontend/src/main.ts` and `frontend/src/app/app.config.ts`. The root shell and route composition are in `frontend/src/app/app.ts`, `frontend/src/app/app.html`, and `frontend/src/app/app.routes.ts`. This layer owns client-side navigation and provides shared application-level HTTP/router configuration.

#### Employee domain contract and API boundary
The shared frontend representation of an employee, including optional ID and creation timestamp, is defined in `frontend/src/app/models/employee.model.ts`. `frontend/src/app/services/employee.service.ts` is the client boundary to `http://localhost:5000`: it issues paginated/search reads and single-record create, update, and delete operations. RxJS/Angular HTTP responses flow from this service into UI components rather than components directly calling the backend.

#### Interactive employee workflow
The home view composes the employee-management experience in `frontend/src/app/components/home/home.component.ts` and its template. `frontend/src/app/components/employee-list/employee-list.component.ts` presents paginated/searchable data and initiates edit/delete actions. `frontend/src/app/components/employee-modal/employee-modal.component.ts` owns validated add/edit form interaction. Successful mutations trigger list refreshes without browser reload; the navbar is a separate navigation component under `frontend/src/app/components/navbar/`.

#### Express API and request processing
`backend/server.js` is the HTTP boundary. It exposes health and `/api/employees` REST endpoints for paginated search, lookup by ID, create, update, and deletion. It also centralizes middleware, request validation, response/error behavior, and API-to-data-layer control flow. The frontend and backend run as independently served processes, normally on ports 4200 and 5000 respectively.

#### Persistence, initialization, and resilience
`backend/db.js` encapsulates PostgreSQL connection and employee CRUD behavior. It initializes the target database/table and seed records where needed, then serves operations through PostgreSQL. If the database is unreachable, this module switches to a pre-seeded in-memory data store, preserving API availability but making fallback-state persistence process-local. PostgreSQL connection details are environment-driven (`PGHOST`, `PGPORT`, `PGUSER`, `PGPASSWORD`, `PGDATABASE`); `.env` is intentionally not committed.

#### Data flow and operational constraints
User input flows modal/list → `EmployeeService` → Express validation/routes → database abstraction → PostgreSQL or memory → JSON response → refreshed Angular state. The backend enforces required names/departments, age range, email format/uniqueness, positive salary, and optional positive custom IDs. PostgreSQL is the only external infrastructure dependency; Node.js 18+, npm, Angular CLI, Express, and the PostgreSQL driver are material runtimes/dependencies, declared through `backend/package.json`, `frontend/package.json`, and root `package.json`.

Main entry points: [`frontend/src/app/services/employee.service.ts`](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/services/employee.service.ts) (Employee service), [`frontend/src/main.ts`](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/main.ts) (Angular bootstrap), [`frontend/src/app/components/home/home.component.ts`](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/home/home.component.ts) (Employee home), [`backend/db.js`](https://github.com/gupthamandavilli/employee_management/blob/main/backend/db.js) (Employee data gateway)

## Diagram (Mermaid)

```mermaid
flowchart TD

subgraph group_frontend["Angular client"]
  node_ng_bootstrap["Angular bootstrap<br/>browser entry<br/>[main.ts]"]
  node_ng_app_config["App configuration<br/>Angular providers<br/>[app.config.ts]"]
  node_ng_shell_routes["App shell and routes<br/>Angular shell<br/>[app.routes.ts]"]
  node_home["Employee home<br/>Angular component<br/>[home.component.ts]"]
  node_employee_list["Employee list<br/>Angular component"]
  node_employee_modal["Employee modal<br/>Angular component"]
  node_employee_service["Employee service<br/>HTTP client boundary"]
  node_employee_model["Employee contract<br/>domain model<br/>[employee.model.ts]"]
end

subgraph group_backend["Express API"]
  node_api_server["Express server<br/>API entry point<br/>[server.js]"]
  node_api_validation["Request validation<br/>API middleware<br/>[server.js]"]
  node_employee_routes["Employee REST routes<br/>API routes<br/>[server.js]"]
end

subgraph group_data["Persistence"]
  node_db_gateway["Employee data gateway<br/>database abstraction<br/>[db.js]"]
  node_postgres[("PostgreSQL<br/>external database")]
  node_memory_store[("In-memory fallback<br/>process-local store<br/>[db.js]")]
end

node_root_package["Workspace commands<br/>npm workspace<br/>[package.json]"]

node_root_package -.->|"starts frontend"| node_ng_bootstrap
node_root_package -.->|"starts backend"| node_api_server
node_ng_bootstrap -->|"loads"| node_ng_app_config
node_ng_bootstrap -->|"boots"| node_ng_shell_routes
node_ng_app_config -->|"provides HTTP"| node_employee_service
node_ng_shell_routes -->|"renders"| node_home
node_home -->|"composes"| node_employee_list
node_home -->|"composes"| node_employee_modal
node_employee_list -->|"loads and mutates"| node_employee_service
node_employee_modal -->|"creates and updates"| node_employee_service
node_employee_service -->|"uses"| node_employee_model
node_employee_service -->|"JSON REST on :5000"| node_api_server
node_api_server -->|"applies"| node_api_validation
node_api_validation -->|"permits requests"| node_employee_routes
node_employee_routes -->|"CRUD operations"| node_db_gateway
node_db_gateway -->|"primary storage"| node_postgres
node_db_gateway -.->|"on database failure"| node_memory_store
node_employee_service -->|"refreshes state"| node_employee_list

click node_root_package "https://github.com/gupthamandavilli/employee_management/blob/main/package.json"
click node_ng_bootstrap "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/main.ts"
click node_ng_app_config "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/app.config.ts"
click node_ng_shell_routes "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/app.routes.ts"
click node_home "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/home/home.component.ts"
click node_employee_list "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/employee-list/employee-list.component.ts"
click node_employee_modal "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/employee-modal/employee-modal.component.ts"
click node_employee_service "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/services/employee.service.ts"
click node_employee_model "https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/models/employee.model.ts"
click node_api_server "https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js"
click node_api_validation "https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js"
click node_employee_routes "https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js"
click node_db_gateway "https://github.com/gupthamandavilli/employee_management/blob/main/backend/db.js"
click node_memory_store "https://github.com/gupthamandavilli/employee_management/blob/main/backend/db.js"

classDef toneNeutral fill:#f8fafc,stroke:#334155,stroke-width:1.5px,color:#0f172a
classDef toneBlue fill:#dbeafe,stroke:#2563eb,stroke-width:1.5px,color:#172554
classDef toneAmber fill:#fef3c7,stroke:#d97706,stroke-width:1.5px,color:#78350f
classDef toneMint fill:#dcfce7,stroke:#16a34a,stroke-width:1.5px,color:#14532d
classDef toneRose fill:#ffe4e6,stroke:#e11d48,stroke-width:1.5px,color:#881337
classDef toneIndigo fill:#e0e7ff,stroke:#4f46e5,stroke-width:1.5px,color:#312e81
classDef toneTeal fill:#ccfbf1,stroke:#0f766e,stroke-width:1.5px,color:#134e4a
class node_ng_bootstrap,node_ng_app_config,node_ng_shell_routes,node_home,node_employee_list,node_employee_modal,node_employee_service,node_employee_model toneBlue
class node_api_server,node_api_validation,node_employee_routes toneAmber
class node_db_gateway,node_postgres,node_memory_store toneMint
class node_root_package toneNeutral
```

## Components

### Angular client

- [Angular bootstrap](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/main.ts): browser entry · `frontend/src/main.ts`
- [App configuration](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/app.config.ts): Angular providers · Provides shared HTTP and router configuration. · `frontend/src/app/app.config.ts`
- [App shell and routes](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/app.routes.ts): Angular shell · Owns client navigation and view composition. · `frontend/src/app/app.routes.ts`
- [Employee home](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/home/home.component.ts): Angular component · Composes the employee-management workflow. · `frontend/src/app/components/home/home.component.ts`
- [Employee list](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/employee-list/employee-list.component.ts): Angular component · Displays searchable, paginated employees and starts edit/delete actions. · `frontend/src/app/components/employee-list/employee-list.component.ts`
- [Employee modal](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/components/employee-modal/employee-modal.component.ts): Angular component · Owns validated add and edit forms. · `frontend/src/app/components/employee-modal/employee-modal.component.ts`
- [Employee service](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/services/employee.service.ts): HTTP client boundary · Issues employee CRUD, pagination, and search requests. · `frontend/src/app/services/employee.service.ts`
- [Employee contract](https://github.com/gupthamandavilli/employee_management/blob/main/frontend/src/app/models/employee.model.ts): domain model · Client employee representation with optional ID and timestamp. · `frontend/src/app/models/employee.model.ts`

### Express API

- [Express server](https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js): API entry point · Serves health and employee REST endpoints on port 5000. · `backend/server.js`
- [Request validation](https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js): API middleware · Enforces employee fields, ranges, formats, and uniqueness rules. · `backend/server.js`
- [Employee REST routes](https://github.com/gupthamandavilli/employee_management/blob/main/backend/server.js): API routes · Handles search, lookup, create, update, and delete operations. · `backend/server.js`

### Persistence

- [Employee data gateway](https://github.com/gupthamandavilli/employee_management/blob/main/backend/db.js): database abstraction · Initializes data and selects PostgreSQL or resilient memory storage. · `backend/db.js`
- **PostgreSQL**: external database · Environment-configured durable employee store.
- [In-memory fallback](https://github.com/gupthamandavilli/employee_management/blob/main/backend/db.js): process-local store · Pre-seeded fallback when PostgreSQL is unreachable. · `backend/db.js`

### Other components

- [Workspace commands](https://github.com/gupthamandavilli/employee_management/blob/main/package.json): npm workspace · Coordinates frontend and backend commands. · `package.json`

## Connections

- Workspace commands → Angular bootstrap: starts frontend
- Workspace commands → Express server: starts backend
- Angular bootstrap → App configuration: loads
- Angular bootstrap → App shell and routes: boots
- App configuration → Employee service: provides HTTP
- App shell and routes → Employee home: renders
- Employee home → Employee list: composes
- Employee home → Employee modal: composes
- Employee list → Employee service: loads and mutates
- Employee modal → Employee service: creates and updates
- Employee service → Employee contract: uses
- Employee service → Express server: JSON REST on :5000
- Express server → Request validation: applies
- Request validation → Employee REST routes: permits requests
- Employee REST routes → Employee data gateway: CRUD operations
- Employee data gateway → PostgreSQL: primary storage
- Employee data gateway → In-memory fallback: on database failure
- Employee service → Employee list: refreshes state