1 回答
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TA贡献1850条经验 获得超11个赞
可以使用数据加载器(文档)解决问题
我必须为以下数据源实现Topics:
package dataloader
import (
"github.com/graph-gophers/dataloader"
)
type ctxKey string
const (
loadersKey = ctxKey("dataloaders")
)
type TopicReader struct {
conn *sql.DB
}
func (t *TopicReader) GetTopics(ctx context.Context, keys dataloader.Keys) []*dataloader.Result {
topicIDs := make([]string, len(keys))
for ix, key := range keys {
topicIDs[ix] = key.String()
}
res := u.db.Exec(
r.Conn,
"SELECT id, name, level
FROM topics
WHERE id IN (?" + strings.Repeat(",?", len(topicIDs-1)) + ")",
topicIDs...,
)
defer res.Close()
output := make([]*dataloader.Result, len(keys))
for index, _ := range keys {
output[index] = &dataloader.Result{Data: res[index], Error: nil}
}
return output
}
type Loaders struct {
TopicLoader *dataloader.Loader
}
func NewLoaders(conn *sql.DB) *Loaders {
topicReader := &TopicReader{conn: conn}
loaders := &Loaders{
TopicLoader: dataloader.NewBatchedLoader(t.GetTopics),
}
return loaders
}
func Middleware(loaders *Loaders, next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
nextCtx := context.WithValue(r.Context(), loadersKey, loaders)
r = r.WithContext(nextCtx)
next.ServeHTTP(w, r)
})
}
func For(ctx context.Context) *Loaders {
return ctx.Value(loadersKey).(*Loaders)
}
func GetTopic(ctx context.Context, topicID string) (*model.Topic, error) {
loaders := For(ctx)
thunk := loaders.TopicLoader.Load(ctx, dataloader.StringKey(topicID))
result, err := thunk()
if err != nil {
return nil, err
}
return result.(*model.Topic), nil
}
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