Library Management API

A REST API for managing a library catalog and circulation (checkout/return), built with ASP.NET Core 8, Clean Architecture, and MediatR/CQRS.

Tech Stack

Layer	Technology
Framework	.NET 8, ASP.NET Core 8
Database	PostgreSQL 16 (EF Core 8)
CQRS / Mediator	MediatR 12
Validation	FluentValidation
API Docs	Swagger / Swashbuckle
Testing	xUnit, FluentAssertions, WebApplicationFactory
Containerization	Docker Compose

Architecture

Clean Architecture with four projects — dependencies point strictly inward:

LibraryManagement.Domain       ← entities, exceptions (no dependencies)
LibraryManagement.Application  ← commands, queries, validators (MediatR + FluentValidation)
LibraryManagement.Infrastructure ← EF Core, PostgreSQL, migrations
LibraryManagement.API          ← controllers, middleware, DI composition root

classDiagram
    class BaseEntity {
        <<abstract>>
        +Guid Id
        +DateTime CreatedAt
        +DateTime UpdatedAt
    }
    class Author { +string Name, +string? Bio }
    class Genre { +string Name }
    class Publisher { +string Name }
    class Book { +string Title, +string Isbn, +int PublicationYear, +int TotalCopies, +int AvailableCopies }
    class Member { +string FullName, +string Email, +string? PhoneNumber, +bool IsActive }
    class Loan { +DateTime LoanDate, +DateTime DueDate, +DateTime? ReturnDate, +bool IsReturned }
    BaseEntity <|-- Author
    BaseEntity <|-- Genre
    BaseEntity <|-- Publisher
    BaseEntity <|-- Book
    BaseEntity <|-- Member
    BaseEntity <|-- Loan
    Author "1" --> "0..*" Book
    Genre "1" --> "0..*" Book
    Publisher "1" --> "0..*" Book
    Book "1" --> "0..*" Loan
    Member "1" --> "0..*" Loan

Loading

API Endpoints

Catalog

Method	Route	Description
GET	/api/Authors	List authors (paginated, sortable, filterable by name)
GET	/api/Authors/{id}	Get author by ID
POST	/api/Authors	Create author
PUT	/api/Authors/{id}	Update author
DELETE	/api/Authors/{id}	Delete author (blocked if author has books)
GET/POST/PUT/DELETE	/api/Books	CRUD — filter by title, ISBN, author, genre, year, availability
GET/POST/PUT/DELETE	/api/Genres	CRUD
GET/POST/PUT/DELETE	/api/Publishers	CRUD

Members

Method	Route	Description
GET/POST/PUT/DELETE	/api/Members	CRUD — filter by name, email, active status

Circulation

Method	Route	Description
POST	/api/Loans	Checkout a book (requires available copies + active member)
POST	/api/Loans/{id}/return	Return a book
GET	/api/Loans	List loans — filter by member, book, returned, overdue
GET	/api/Loans/{id}	Get loan by ID

Pagination, Sorting & Filtering

All list endpoints return a PagedResult<T> envelope:

{
  "items": [...],
  "pageNumber": 1,
  "pageSize": 10,
  "totalCount": 42,
  "totalPages": 5
}

Query parameters (all optional):

Parameter	Default	Description
pageNumber	1	Page to fetch
pageSize	10	Items per page (max 50)
sortBy	createdAt	Sort field (whitelisted per endpoint)
sortDescending	false	Sort direction
entity-specific		e.g. title, isbn, authorId, isAvailable for Books

Example:

GET /api/Books?title=1984&sortBy=title&sortDescending=false&pageNumber=1&pageSize=5
GET /api/Loans?isOverdue=true&sortBy=dueDate
GET /api/Authors?name=Orwell&sortBy=name

Quick Start

Docker Compose (recommended)

docker compose up -d
# API: http://localhost:8080
# Swagger UI: http://localhost:8080/swagger
# PostgreSQL: localhost:5432 (user: postgres, pass: postgres, db: librarymanagement)

Auto-migrates the database and seeds demo data on first startup (Orwell, Austen, Hemingway, 3 books, 2 members).

Local (without Docker)

Requires .NET 8 SDK and a running PostgreSQL instance.

# Update connection string in LibraryManagement.API/appsettings.Development.json
dotnet restore
dotnet run --project LibraryManagement.API

Testing

dotnet test
# 10 unit tests (handlers + validators, EF InMemory)
# 5 integration tests (full HTTP cycle, WebApplicationFactory + SQLite)

Project Structure

LibraryManagement/
├── LibraryManagement.Domain/          Entities, exceptions
├── LibraryManagement.Application/     Commands, queries, DTOs, validators
│   ├── Authors|Books|Genres|Loans|Members|Publishers/
│   │   ├── Commands/                  Write operations (Create, Update, Delete)
│   │   ├── Queries/                   Read operations (GetById, GetAll)
│   │   ├── Dtos/                      Input/output contracts + filters
│   │   └── Validators/                FluentValidation rules
│   └── Common/                        IAppDbContext, PagedResult, ValidationBehavior
├── LibraryManagement.Infrastructure/  EF Core DbContext, migrations, configurations
├── LibraryManagement.API/             Controllers, middleware, Program.cs
├── tests/
│   ├── LibraryManagement.UnitTests/
│   └── LibraryManagement.IntegrationTests/
├── docs/                              UML diagrams (PlantUML sources)
└── compose.yaml                       Docker Compose (PostgreSQL + API)

Seed Data

On first startup the database is populated with:

• 3 Authors: George Orwell, Jane Austen, Ernest Hemingway
• 3 Genres: Dystopian, Romance, Adventure
• 2 Publishers: Penguin Books, HarperCollins
• 3 Books: 1984, Pride and Prejudice, The Old Man and the Sea
• 2 Members: Alice Johnson, Bob Smith

License

CC0 — Public Domain