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// 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/facebook/ent/examples/o2orecur/ent"
"github.com/facebook/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
}
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