Sample: Simple DbContext ERD

This sample demonstrates Entity Relationship Diagram (ERD) generation for a standard Entity Framework Core DbContext. It showcases how ProjGraph visualizes database schemas including one-to-many, many-to-many, and one-to-one relationships.

🏙️ Domain: Library Management

The domain consists of a simple book management schema:

  • Authors & Books: A many-to-many relationship (AuthorBook join table).
  • Books & Categories: A many-to-many relationship (BookCategory join table).
  • Publishers: A one-to-many relationship with Books.
  • Reviews: A one-to-many relationship for each Book.
  • Profiles & BookDetails: One-to-one relationships providing additional metadata.

📊 Visual Snapshot

Below is the diagram generated for the MyDbContext class using ProjGraph:

---
title: MyDbContext
---
erDiagram
  Author {
    int Id PK
    int MentorId FK
    string Bio "max:1000"
    DateTime BirthDate
    bool IsActive
    string Name "required, max:200"
  }
  AuthorBook {
    int AuthorId PK,FK
    int BookId PK,FK
  }
  Book {
    int Id PK
    int PublisherId FK
    string ISBN "max:13"
    int PageCount
    DateTime PublishedDate
    string Title "required, max:300"
  }
  BookCategory {
    int BookId PK,FK
    int CategoryId PK,FK
  }
  BookDetail {
    int Id PK
    int BookId FK
    string Notes "required"
    string Summary "required"
  }
  Category {
    int Id PK
    string Description "max:500"
    string Name "required, max:100"
  }
  Profile {
    int Id PK
    int AuthorId FK
    string AvatarUrl "required"
    string BioData "required"
  }
  Publisher {
    int Id PK
    string Country "max:100"
    DateTime FoundedDate
    string Name "required, max:200"
  }
  Review {
    int Id PK
    int BookId FK
    string Comment "max:2000"
    int Rating "required"
    DateTime ReviewDate
  }
  Author ||--o{ Author : ""
  Author ||--o{ AuthorBook : ""
  Author |o--|| Profile : ""
  Book ||--o{ AuthorBook : ""
  Book ||--o{ BookCategory : ""
  Book ||--|| BookDetail : ""
  Book ||--o{ Review : ""
  Category ||--o{ BookCategory : ""
  Publisher ||--o{ Book : ""
Tip

This diagram was generated directly from the DbContext source. You can find the latest snapshot in simple-context.mmd.

🚀 Quick Start

To generate this diagram yourself, run the following command from the repository root:

projgraph erd ./samples/erd/simple-context/EntityFramework/MyDbContext.cs > ./samples/erd/simple-context/simple-context.mmd

🛠️ Build and Test

This project is a standard .NET 10 project using EF Core. You can build it using:

dotnet build ./samples/erd/simple-context/

Example Output

---
title: MyDbContext
---
erDiagram
  Author {
    int Id PK
    int MentorId FK
    string Bio "max:1000"
    DateTime BirthDate
    bool IsActive
    string Name "required, max:200"
  }
  AuthorBook {
    int AuthorId PK,FK
    int BookId PK,FK
  }
  Book {
    int Id PK
    int PublisherId FK
    string ISBN "max:13"
    int PageCount
    DateTime PublishedDate
    string Title "required, max:300"
  }
  BookCategory {
    int BookId PK,FK
    int CategoryId PK,FK
  }
  BookDetail {
    int Id PK
    int BookId FK
    string Notes "required"
    string Summary "required"
  }
  Category {
    int Id PK
    string Description "max:500"
    string Name "required, max:100"
  }
  Profile {
    int Id PK
    int AuthorId FK
    string AvatarUrl "required"
    string BioData "required"
  }
  Publisher {
    int Id PK
    string Country "max:100"
    DateTime FoundedDate
    string Name "required, max:200"
  }
  Review {
    int Id PK
    int BookId FK
    string Comment "max:2000"
    int Rating "required"
    DateTime ReviewDate
  }
  Author ||--o{ Author : ""
  Author ||--o{ AuthorBook : ""
  Author |o--|| Profile : ""
  Book ||--o{ AuthorBook : ""
  Book ||--o{ BookCategory : ""
  Book ||--|| BookDetail : ""
  Book ||--o{ Review : ""
  Category ||--o{ BookCategory : ""
  Publisher ||--o{ Book : ""

Rendered Diagram

The Mermaid diagram renders as a visual ERD showing:

  • Entity boxes with all properties and their types
  • Relationship lines with cardinality indicators:
    • ||--o{ = One-to-Many (required)
    • |o--o{ = One-to-Many (optional)
    • ||--|| = One-to-One (required)
    • ||--o| = One-to-One (optional)
    • }|--|{ = Many-to-Many (shown as two One-to-Many via join table)

Key Features

✅ Direct DbContext File Analysis

  • DbContext files (.cs) - Direct analysis of DbContext classes
  • Auto-detection - Finds *DbContext.cs files in current directory
  • No build required - Works with source code directly
  • Inheritance support - Includes properties from base classes (e.g., AuditEntity, BaseEntity)

✅ Comprehensive Type Information

  • Sanitized types for Mermaid compatibility (removes ?, <>, [])
  • Original type comments showing exact C# types including nullability
  • Validation constraints extracted from data annotations and Fluent API:
    • required - Fields marked as required (non-nullable or [Required])
    • max:N - Maximum length constraints from [MaxLength] or HasMaxLength()
    • precision(P,S) - Decimal precision and scale from [Column] or HasPrecision()
    • default:value - Default values from HasDefaultValue()
  • Example: string Name "string? | required, max:200" shows original type, required status, and max length

✅ Explicit Join Tables

  • Many-to-many relationships are shown as explicit join tables
  • Join tables include composite primary/foreign keys
  • Clear visualization of the actual database structure
  • Example: AuthorBook table with AuthorId and BookId columns

✅ Proper Relationship Detection

  • One-to-Many: Correctly identifies parent-child relationships
  • One-to-One: Detects bidirectional single references
  • Many-to-Many: Discovers collection navigations on both sides
  • Inverse navigation analysis: Determines relationship direction from code

✅ Clean Output

  • No duplicate properties or relationships
  • Valid Mermaid syntax (comma-separated PK,FK markers)
  • Consistent label formatting for all relationships
  • Entity names and labels properly trimmed

Advanced Usage

Save to File

# Save the ERD diagram to a file
projgraph erd EntityFramework/MyDbContext.cs > erd-diagram.mmd

# Or save to markdown for documentation
projgraph erd EntityFramework/MyDbContext.cs > docs/database-schema.md

Integration with Documentation

The output is GitHub/GitLab compatible Mermaid syntax, so you can:

  1. Copy the output directly into your README.md
  2. Commit it to version control
  3. It will render automatically in GitHub, GitLab, and other platforms
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