mirror of
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c53b45ddb0
* all: use %w instead of %v for nested errors with fmt.Errorf * all: update generated code to use %w instead of %v for error wrapping
87 lines
2.0 KiB
Go
87 lines
2.0 KiB
Go
// Copyright 2019-present Facebook Inc. All rights reserved.
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// This source code is licensed under the Apache 2.0 license found
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// in the LICENSE file in the root directory of this source tree.
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package main
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import (
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"context"
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"fmt"
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"log"
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"entgo.io/ent/examples/o2orecur/ent"
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"entgo.io/ent/examples/o2orecur/ent/node"
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_ "github.com/mattn/go-sqlite3"
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)
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func Example_O2ORecur() {
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client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
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if err != nil {
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log.Fatalf("failed opening connection to sqlite: %v", err)
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}
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defer client.Close()
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ctx := context.Background()
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// Run the auto migration tool.
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if err := client.Schema.Create(ctx); err != nil {
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log.Fatalf("failed creating schema resources: %v", err)
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}
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if err := Do(ctx, client); err != nil {
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log.Fatal(err)
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}
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// Output:
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// 1 2 3 4 5
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// true
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}
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func Do(ctx context.Context, client *ent.Client) error {
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head, err := client.Node.
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Create().
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SetValue(1).
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Save(ctx)
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if err != nil {
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return fmt.Errorf("creating the head: %w", err)
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}
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curr := head
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// Generate the following linked-list: 1<->2<->3<->4<->5.
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for i := 0; i < 4; i++ {
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curr, err = client.Node.
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Create().
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SetValue(curr.Value + 1).
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SetPrev(curr).
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Save(ctx)
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if err != nil {
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return err
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}
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}
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// Loop over the list and print it. `FirstX` panics if an error occur.
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for curr = head; curr != nil; curr = curr.QueryNext().FirstX(ctx) {
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fmt.Printf(" %d", curr.Value)
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}
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// Output: 1 2 3 4 5
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// Make the linked-list circular:
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// The tail of the list, has no "next".
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tail, err := client.Node.
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Query().
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Where(node.Not(node.HasNext())).
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Only(ctx)
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if err != nil {
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return fmt.Errorf("getting the tail of the list: %v", tail)
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}
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tail, err = tail.Update().SetNext(head).Save(ctx)
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if err != nil {
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return err
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}
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// Check that the change actually applied:
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prev, err := head.QueryPrev().Only(ctx)
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if err != nil {
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return fmt.Errorf("getting head's prev: %w", err)
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}
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fmt.Printf("\n%v", prev.Value == tail.Value)
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// Output: true
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return nil
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}
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