Graph Traversal

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

    Add the necessary fields and edges for the schemas:

    ent/schema/pet.go

    1. // Pet holds the schema definition for the Pet entity.
    2. type Pet struct {
    3.     ent.Schema
    4. }
    6. // Fields of the Pet.
    7. func (Pet) Fields() []ent.Field {
    8.     return []ent.Field{
    9.         field.String("name"),
    10.     }
    11. }
    13. // Edges of the Pet.
    14. func (Pet) Edges() []ent.Edge {
    15.     return []ent.Edge{
    16.         edge.To("friends", Pet.Type),
    17.         edge.From("owner", User.Type).
    18.             Ref("pets").
    19.             Unique(),

    ent/schema/group.go

    1. // Group holds the schema definition for the Group entity.
    2. type Group struct {
    3.     ent.Schema
    4. }
    6. // Fields of the Group.
    7. func (Group) Fields() []ent.Field {
    8.     return []ent.Field{
    9.         field.String("name"),
    10.     }
    11. }
    13. // Edges of the Group.
    14. func (Group) Edges() []ent.Edge {
    15.     return []ent.Edge{
    16.         edge.To("users", User.Type),
    17.         edge.To("admin", User.Type).
    18.             Unique(),
    19. }

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

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

    er-traversal-graph-gopher

    1. func Traverse(ctx context.Context, client *ent.Client) error {
    2.     owner, err := client.Group.         // GroupClient.
    3.         Query().                        // Query builder.
    4.         Where(group.Name("Github")).    // Filter only Github group (only 1).
    5.         QueryAdmin().                   // Getting Dan.
    6.         QueryFriends().                 // Getting Dan's friends: [Ariel].
    7.         QueryPets().                    // Their pets: [Pedro, Xabi].
    8.         QueryFriends().                 // Pedro's friends: [Coco], Xabi's friends: [].
    9.         QueryOwner().                   // Coco's owner: Alex.
    10.         Only(ctx)                       // Expect only one entity to return in the query.
    11.     if err != nil {
    12.         return fmt.Errorf("failed querying the owner: %w", err)
    13.     }
    14.     fmt.Println(owner)
    15.     // Output:
    16.     // User(id=3, age=37, name=Alex)
    17.     return nil
    18. }

    What about the following traversal?

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

    The full example exists in GitHub.