panel-go-relationship

name	panel-go-relationship
description	Implement database relationships for Panel.go with BelongsTo, HasMany, HasOne, BelongsToMany, and polymorphic relationships. Use when adding relationships between entities or configuring eager loading. See panel-go-plugin-scaffold for comprehensive examples with --with-example flag. Use when this capability is needed.
metadata	{"author":"ferdiunal"}

Panel.go Relationship Expert

Expert in implementing database relationships for Panel.go with BelongsTo, HasMany, HasOne, BelongsToMany, and polymorphic relationships.

Expertise

• BelongsTo: One-to-one, child to parent (Post belongs to User)
• HasOne: One-to-one, parent to child (User has one Profile)
• HasMany: One-to-many (User has many Posts)
• BelongsToMany: Many-to-many (Post belongs to many Tags)
• MorphTo: Polymorphic relationships (Comment belongs to Commentable)
• MorphToMany: Polymorphic many-to-many (Tag belongs to many Taggables)
• Eager Loading: Preload, Joins to prevent N+1
• Entity.go Pattern: All entities in one file to prevent circular dependency
• Registry Pattern: Resource access without direct imports

Quick Patterns

BelongsTo

type Post struct {
    ID     uint
    UserID uint
    User   *User `gorm:"foreignKey:UserID;constraint:OnUpdate:CASCADE,OnDelete:CASCADE"`
}

fields.BelongsTo("User", "user_id", resources.GetOrPanic("users")).
    DisplayUsing("name").
    WithSearchableColumns("name", "email").
    WithEagerLoad()

HasMany

type User struct {
    ID    uint
    Posts []Post `gorm:"foreignKey:UserID"`
}

fields.HasMany("Posts", "posts", resources.GetOrPanic("posts")).
    ForeignKey("user_id").
    OwnerKey("id").
    WithEagerLoad()

HasOne

type Organization struct {
    ID          uint
    BillingInfo *BillingInfo `gorm:"foreignKey:OrganizationID"`
}

type BillingInfo struct {
    ID             uint
    OrganizationID uint `gorm:"not null;unique;index"`
    Organization   *Organization
}

fields.HasOne("BillingInfo", "billing_info", resources.GetOrPanic("billing-info")).
    ForeignKey("organization_id").
    OwnerKey("id").
    WithEagerLoad()

BelongsToMany

type Post struct {
    ID   uint
    Tags []Tag `gorm:"many2many:post_tags;"`
}

type Tag struct {
    ID    uint
    Posts []Post `gorm:"many2many:post_tags;"`
}

fields.BelongsToMany("Tags", "tags", resources.GetOrPanic("tags")).
    PivotTable("post_tags").
    WithEagerLoad()

MorphTo (Polymorphic)

type Comment struct {
    ID              uint
    CommentableID   uint   `gorm:"index:idx_commentable"`
    CommentableType string `gorm:"index:idx_commentable"`
    Content         string
}

// Entity'de tanımlanır, ancak field henüz implement edilmemiş

MorphToMany (Polymorphic Many-to-Many)

type Tag struct {
    ID   uint
    Name string
}

// Taggable pivot table ile Product ve Shipment'a bağlanır
// Entity'de tanımlanır, ancak field henüz implement edilmemiş

Eager Loading

func (r *PostResource) With() []string {
    return []string{"User", "Category", "Tags"}
}

Entity.go Pattern

Tüm entity'leri tek dosyada tut (circular dependency önlenir):

// entity/entity.go
package entity

type Organization struct {
    ID          uint
    Addresses   []Address    // HasMany
    BillingInfo *BillingInfo // HasOne
}

type Address struct {
    ID             uint
    OrganizationID uint
    Organization   *Organization // BelongsTo
}

type BillingInfo struct {
    ID             uint
    OrganizationID uint `gorm:"unique"`
    Organization   *Organization // BelongsTo (HasOne)
}

Registry Pattern

Resource'lar birbirini import etmeden erişir:

// resources/registry.go
var registry = make(map[string]func() resource.Resource)

func Register(slug string, factory func() resource.Resource) {
    registry[slug] = factory
    resource.Register(slug, factory())
}

func GetOrPanic(slug string) resource.Resource {
    if r := Get(slug); r != nil {
        return r
    }
    panic("resource not found: " + slug)
}

// Kullanım
fields.HasMany("Addresses", "addresses", resources.GetOrPanic("addresses"))

Key Rules

• Always index foreign keys
• Use Preload to prevent N+1 queries
• Define cascade rules (CASCADE, RESTRICT, SET NULL)
• Set DisplayKey for relationships
• Add With() method for eager loading
• Use entity.go pattern for all entities
• Use registry pattern for resource access

Usage

When user asks to add relationships:

1. Add foreign key to entity in entity/entity.go
2. Add relationship field with GORM tags
3. Add relationship field to field resolver using resources.GetOrPanic()
4. Set DisplayUsing, WithSearchableColumns, WithEagerLoad
5. Add eager loading in With() method

Comprehensive Examples

For comprehensive examples with all relationship types:

panel plugin create example --with-example

This creates 9 entities and 7 resources demonstrating:

• BelongsTo, HasMany, HasOne, BelongsToMany
• MorphTo, MorphToMany (entity level)
• Entity.go pattern
• Registry pattern

See panel-go-plugin-scaffold skill for details.

Anti-Patterns

❌ Don't forget foreign key indexes - Always index foreign keys ❌ Don't skip eager loading - Use With() to prevent N+1 queries ❌ Don't forget DisplayUsing - Set DisplayUsing for relationship fields ❌ Don't skip cascade rules - Define OnUpdate and OnDelete behavior ❌ Don't use wrong field types - BelongsTo for belongs_to, HasMany for has_many, etc. ❌ Don't separate entities - Use entity.go pattern to prevent circular dependency ❌ Don't import resources directly - Use registry pattern

Sharp Edges

⚠️ N+1 Queries: Always use WithEagerLoad() for relationships ⚠️ Cascade Deletes: Be careful with CASCADE on delete ⚠️ Many-to-Many: Requires junction table (many2many tag) ⚠️ DisplayUsing: Must match actual field name in related entity ⚠️ Polymorphic: MorphTo/MorphToMany fields not yet implemented in panel.go ⚠️ Circular Dependency: Use entity.go pattern to prevent import cycles ⚠️ Registry Timing: init() functions run on import, order matters

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