Domain Layer Guide

What Belongs in Domain (core/domain/)

The domain layer contains pure Go structs with no external dependencies — no database tags, no framework imports, no HTTP/GraphQL code. You should be able to copy domain files to another project and compile them with only the standard library.

Include	Do NOT Include
Business entities (structs)	Database tags (db:"column")
Constants/enums (ContentType, Privacy)	SQL queries
Domain errors (ErrNotFound, ErrInvalidRating)	HTTP/GraphQL code
Validation methods	External API calls

Core Entities

• Content - Media that users create perspectives on (YouTube videos, articles)
• Perspective - A user's viewpoint/rating on content (claim, quality, agreement, etc.)

Optional Fields Pattern

Use pointers for nullable/optional fields:

type Perspective struct {
    Claim   string  // Required - always has a value
    Quality *int    // Optional - nil means "not provided"
}

// Check if optional field is set
if p.Quality != nil {
    fmt.Println(*p.Quality)  // Dereference to get value
}

// Set an optional field
quality := 85
p.Quality = &quality

Request Flow

GraphQL Request
  → GraphQL Resolver (adapter)
  → Domain Service (core, uses port interfaces)
  → Repository Interface (port)
  → PostgreSQL Repository (adapter)