examples: make examples testable

examples/o2orecur/example_test.go

@@ -0,0 +1,86 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/facebookincubator/ent/examples/o2orecur/ent"
+	"github.com/facebookincubator/ent/examples/o2orecur/ent/node"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+func Example_O2ORecur() {
+	client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
+	if err != nil {
+		log.Fatalf("failed opening connection to sqlite: %v", err)
+	}
+	defer client.Close()
+	ctx := context.Background()
+	// Run the auto migration tool.
+	if err := client.Schema.Create(ctx); err != nil {
+		log.Fatalf("failed creating schema resources: %v", err)
+	}
+	if err := Do(ctx, client); err != nil {
+		log.Fatal(err)
+	}
+	// Output:
+	// 1 2 3 4 5
+	// true
+}
+
+func Do(ctx context.Context, client *ent.Client) error {
+	head, err := client.Node.
+		Create().
+		SetValue(1).
+		Save(ctx)
+	if err != nil {
+		return fmt.Errorf("creating the head: %v", err)
+	}
+	curr := head
+	// Generate the following linked-list: 1<->2<->3<->4<->5.
+	for i := 0; i < 4; i++ {
+		curr, err = client.Node.
+			Create().
+			SetValue(curr.Value + 1).
+			SetPrev(curr).
+			Save(ctx)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Loop over the list and print it. `FirstX` panics if an error occur.
+	for curr = head; curr != nil; curr = curr.QueryNext().FirstX(ctx) {
+		fmt.Printf(" %d", curr.Value)
+	}
+	// Output: 1 2 3 4 5
+
+	// Make the linked-list circular:
+	// The tail of the list, has no "next".
+	tail, err := client.Node.
+		Query().
+		Where(node.Not(node.HasNext())).
+		Only(ctx)
+	if err != nil {
+		return fmt.Errorf("getting the tail of the list: %v", tail)
+	}
+	tail, err = tail.Update().SetNext(head).Save(ctx)
+	if err != nil {
+		return err
+	}
+	// Check that the change actually applied:
+	prev, err := head.QueryPrev().Only(ctx)
+	if err != nil {
+		return fmt.Errorf("getting head's prev: %v", err)
+	}
+	fmt.Printf("\n%v", prev.Value == tail.Value)
+	// Output: true
+
+	return nil
+}