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Graph Traversal

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

er-traversal-graph

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

go run 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:

er-traversal-graph-gopher

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?

er-traversal-graph-gopher-query

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.