Relations

Relations define how models are connected to each other. forge supports ForeignKey, OneToOne, and ManyToMany relationships (one-to-many is represented by a ForeignKey with a RelatedName).

Complete reference for model relationships.

Relation Types

ForeignKey (Many-to-One)

A many-to-one relationship:

import "github.com/forgego/forge/schema"

func (Post) Relations() []schema.Relation {
    return []schema.Relation{
        schema.ForeignKeyField("author", "User",
            schema.OnDelete(schema.CascadeCASCADE),
            schema.RelatedName("posts"),
        ),
    }
}

Access:

post.Author  // *User
user.Posts   // []*Post (reverse)

OneToOne

A one-to-one relationship:

func (User) Relations() []schema.Relation {
    return []schema.Relation{
        schema.OneToOneField("profile", "UserProfile",
            schema.OnDelete(schema.CascadeCASCADE),
        ),
    }
}

Access:

user.Profile    // *UserProfile
profile.User    // *User (reverse)

ManyToMany

A many-to-many relationship:

func (Post) Relations() []schema.Relation {
    return []schema.Relation{
        schema.ManyToManyField("tags", "Tag",
            schema.Through("post_tags"),
            schema.RelatedName("posts"),
        ),
    }
}

Access:

post.Tags  // []*Tag
tag.Posts  // []*Post (reverse)

Relation Options

OnDelete

Cascade behavior on delete:

schema.ForeignKeyField("author", "User",
    schema.OnDelete(schema.CascadeCASCADE),
    // schema.OnDelete(schema.CascadeSET_NULL),
    // schema.OnDelete(schema.CascadeSET_DEFAULT),
    // schema.OnDelete(schema.CascadePROTECT),   // Prevent deletion
    // schema.OnDelete(schema.CascadeDO_NOTHING), // No action
)

OnUpdate

Cascade behavior on update:

schema.ForeignKeyField("author", "User",
    schema.OnUpdate(schema.CascadeCASCADE),
)

RelatedName

Reverse relation name:

schema.ForeignKeyField("author", "User",
    schema.RelatedName("posts"),
)

Through

Through table for ManyToMany:

schema.ManyToManyField("tags", "Tag",
    schema.Through("post_tags"),
)

DBConstraint

Control FK constraint creation:

schema.ForeignKeyField("author", "User",
    schema.DBConstraint(true),
)

Cascade Options

Option	SQL	Description
CascadeCASCADE	ON DELETE CASCADE	Delete related objects
CascadeSET_NULL	ON DELETE SET NULL	Set foreign key to NULL
CascadeSET_DEFAULT	ON DELETE SET DEFAULT	Set foreign key to default
CascadePROTECT	ON DELETE RESTRICT	Prevent deletion if related objects exist
CascadeDO_NOTHING	ON DELETE NO ACTION	No action (database default)

Examples

Blog Post with Author

type Post struct {
    schema.BaseSchema
}

func (Post) Relations() []schema.Relation {
    return []schema.Relation{
        schema.ForeignKeyField("author", "User",
            schema.OnDelete(schema.CascadeCASCADE),
            schema.RelatedName("posts"),
        ),
    }
}

User with Profile

type User struct {
    schema.BaseSchema
}

func (User) Relations() []schema.Relation {
    return []schema.Relation{
        schema.OneToOneField("profile", "UserProfile",
            schema.OnDelete(schema.CascadeCASCADE),
        ),
    }
}

Post with Tags

type Post struct {
    schema.BaseSchema
}

func (Post) Relations() []schema.Relation {
    return []schema.Relation{
        schema.ManyToManyField("tags", "Tag",
            schema.Through("post_tags"),
            schema.RelatedName("posts"),
        ),
    }
}

See Also

• Models Guide - Model usage guide
• Queries Guide - Querying relations