实现 App Engine Go 中一对多关系的教程

import (
    "time"

    "cloud.google.com/go/datastore"
)

type Comment struct {
    Author  string
    Content string
    Date    time.Time
}

type Vote struct {
    User       string
    Score      int
    CommentKey *datastore.Key
}

import (
    "context"
    "fmt"
    "log"

    "cloud.google.com/go/datastore"
    "google.golang.org/api/iterator"
)

func GetVotesForComment(ctx context.Context, client *datastore.Client, commentKey *datastore.Key) ([]Vote, error) {
    var votes []Vote

    q := datastore.NewQuery("Vote").Filter("CommentKey =", commentKey)
    it := client.Run(ctx, q)
    for {
        var vote Vote
        key, err := it.Next(&vote)
        if err == iterator.Done {
            break
        }
        if err != nil {
            return nil, fmt.Errorf("failed to fetch next Vote: %v", err)
        }
        vote.CommentKey = key // Store the key for potential later use

        votes = append(votes, vote)
    }

    return votes, nil
}

func main() {
    ctx := context.Background()
    projectID := "your-project-id" // Replace with your Google Cloud project ID

    client, err := datastore.NewClient(ctx, projectID)
    if err != nil {
        log.Fatalf("Failed to create client: %v", err)
    }
    defer client.Close()

    // Create a dummy comment
    comment := Comment{
        Author:  "Test Author",
        Content: "Test Content",
        Date:    time.Now(),
    }

    // Save the comment to Datastore
    commentKey := datastore.NameKey("Comment", "test-comment", nil)
    commentKey, err = client.Put(ctx, commentKey, &comment)
    if err != nil {
        log.Fatalf("Failed to save comment: %v", err)
    }

    // Create some dummy votes associated with the comment
    vote1 := Vote{
        User:       "User1",
        Score:      5,
        CommentKey: commentKey,
    }
    vote2 := Vote{
        User:       "User2",
        Score:      3,
        CommentKey: commentKey,
    }

    // Save the votes to Datastore
    _, err = client.Put(ctx, datastore.IncompleteKey("Vote", commentKey), &vote1)
    if err != nil {
        log.Fatalf("Failed to save vote1: %v", err)
    }
    _, err = client.Put(ctx, datastore.IncompleteKey("Vote", commentKey), &vote2)
    if err != nil {
        log.Fatalf("Failed to save vote2: %v", err)
    }

    // Retrieve all votes associated with the comment
    votes, err := GetVotesForComment(ctx, client, commentKey)
    if err != nil {
        log.Fatalf("Failed to retrieve votes: %v", err)
    }

    // Print the retrieved votes
    fmt.Println("Votes for comment:")
    for _, vote := range votes {
        fmt.Printf("  User: %s, Score: %d\n", vote.User, vote.Score)
    }
}