ent/doc/md/traversals.md

id, title

id	title
traversals	Graph Traversal

For the purpose of the example, we'll generate the following graph:

The first step is to generate the 3 schemas: Pet, User, Group.

go run -mod=mod entgo.io/ent/cmd/ent init Pet User Group

Add the necessary fields and edges for the schemas:

ent/schema/pet.go

// Pet holds the schema definition for the Pet entity.
type Pet struct {
	ent.Schema
}

// Fields of the Pet.
func (Pet) Fields() []ent.Field {
	return []ent.Field{
		field.String("name"),
	}
}

// Edges of the Pet.
func (Pet) Edges() []ent.Edge {
	return []ent.Edge{
		edge.To("friends", Pet.Type),
		edge.From("owner", User.Type).
			Ref("pets").
			Unique(),
	}
}

ent/schema/user.go

// User holds the schema definition for the User entity.
type User struct {
	ent.Schema
}

// Fields of the User.
func (User) Fields() []ent.Field {
	return []ent.Field{
		field.Int("age"),
		field.String("name"),
	}
}

// Edges of the User.
func (User) Edges() []ent.Edge {
	return []ent.Edge{
		edge.To("pets", Pet.Type),
		edge.To("friends", User.Type),
		edge.From("groups", Group.Type).
			Ref("users"),
		edge.From("manage", Group.Type).
			Ref("admin"),
	}
}

ent/schema/group.go

// Group holds the schema definition for the Group entity.
type Group struct {
	ent.Schema
}

// Fields of the Group.
func (Group) Fields() []ent.Field {
	return []ent.Field{
		field.String("name"),
	}
}

// Edges of the Group.
func (Group) Edges() []ent.Edge {
	return []ent.Edge{
		edge.To("users", User.Type),
		edge.To("admin", User.Type).
			Unique(),
	}
}

Let's write the code for populating the vertices and the edges to the graph:

func Gen(ctx context.Context, client *ent.Client) error {
	hub, err := client.Group.
		Create().
		SetName("Github").
		Save(ctx)
	if err != nil {
		return fmt.Errorf("failed creating the group: %w", err)
	}
	// Create the admin of the group.
	// Unlike `Save`, `SaveX` panics if an error occurs.
	dan := client.User.
		Create().
		SetAge(29).
		SetName("Dan").
		AddManage(hub).
		SaveX(ctx)

	// Create "Ariel" and its pets.
	a8m := client.User.
		Create().
		SetAge(30).
		SetName("Ariel").
		AddGroups(hub).
		AddFriends(dan).
		SaveX(ctx)
	pedro := client.Pet.
		Create().
		SetName("Pedro").
		SetOwner(a8m).
		SaveX(ctx)
	xabi := client.Pet.
		Create().
		SetName("Xabi").
		SetOwner(a8m).
		SaveX(ctx)

	// Create "Alex" and its pets.
	alex := client.User.
		Create().
		SetAge(37).
		SetName("Alex").
		SaveX(ctx)
	coco := client.Pet.
		Create().
		SetName("Coco").
		SetOwner(alex).
		AddFriends(pedro).
		SaveX(ctx)

	fmt.Println("Pets created:", pedro, xabi, coco)
	// Output:
	// Pets created: Pet(id=1, name=Pedro) Pet(id=2, name=Xabi) Pet(id=3, name=Coco)
	return nil
}

Let's go over a few traversals, and show the code for them:

The traversal above starts from a Group entity, continues to its admin (edge), continues to its friends (edge), gets their pets (edge), gets each pet's friends (edge), and requests their owners.

func Traverse(ctx context.Context, client *ent.Client) error {
	owner, err := client.Group.			// GroupClient.
		Query().                     	// Query builder.
		Where(group.Name("Github")). 	// Filter only Github group (only 1).
		QueryAdmin().                	// Getting Dan.
		QueryFriends().              	// Getting Dan's friends: [Ariel].
		QueryPets().                 	// Their pets: [Pedro, Xabi].
		QueryFriends().              	// Pedro's friends: [Coco], Xabi's friends: [].
		QueryOwner().                	// Coco's owner: Alex.
		Only(ctx)                    	// Expect only one entity to return in the query.
	if err != nil {
		return fmt.Errorf("failed querying the owner: %w", err)
	}
	fmt.Println(owner)
	// Output:
	// User(id=3, age=37, name=Alex)
	return nil
}

What about the following traversal?

We want to get all pets (entities) that have an owner (edge) that is a friend (edge) of some group admin (edge).

func Traverse(ctx context.Context, client *ent.Client) error {
	pets, err := client.Pet.
		Query().
		Where(
			pet.HasOwnerWith(
				user.HasFriendsWith(
					user.HasManage(),
				),
			),
		).
		All(ctx)
	if err != nil {
		return fmt.Errorf("failed querying the pets: %w", err)
	}
	fmt.Println(pets)
	// Output:
	// [Pet(id=1, name=Pedro) Pet(id=2, name=Xabi)]
	return nil
}

The full example exists in GitHub.