英文:
incorrectly drafted MongoDB aggregation pipeline $match stage
问题
我正在尝试使用go.mongodb.org/mongo-driver/mongo库在golang语言中进行查询（下面我附上了纯mongodb查询的工作代码），以下是golang查询代码。我无法正确使用matchStage，我尝试了许多变体，我确定我只是非常粗心或者根本不理解。
如何同时使用$match、$expr、$and和$lte来创建一个正确的matchStage？
func (r *Mongo) ChatHistory(ctx context.Context, chatID string, f *Filter) ([]*Message, error) {matchStage := bson.D{primitive.E{Key: "$match",Value: bson.D{primitive.E{Key: "$expr", Value: bson.D{primitive.E{Key: "$and", Value: bson.A{bson.D{primitive.E{Key: "$lte", Value: bson.D{primitive.E{Key: "$create_date",Value: f.Date, // int64},}},},}},}},},},}sortStage := bson.D{{Key: "$sort", Value: bson.D{primitive.E{Key: "create_date", Value: -1},},},}limitStage := bson.D{primitive.E{Key: "$limit", Value: f.Count}}cursor, err := r.colMessage.Aggregate(ctx, mongo.Pipeline{matchStage, sortStage, limitStage})if err != nil {l.Error().Err(err).Msg("failed find")return nil, err}var res []*Messageif err = cursor.All(ctx, &res); err != nil {l.Error().Err(err).Msg("failed find all documents")return nil, err}if err = cursor.Close(ctx); err != nil {l.Error().Err(err).Msg("failed close cursor")return nil, err}return res, nil}
错误：(InvalidPipelineOperator) Unrecognized expression '$create_date'
英文:
I'm trying to make a query in golang language (below I've attached working code of pure mongodb query) using go.mongodb.org/mongo-driver/mongo library, below is golang query code. I can't get matchStage to work correctly, I've tried many variants and I'm sure I'm just very inattentive or just don't understand
How can I use $match, $expr, $and and $lte at once to make a correct matchStage?
func (r *Mongo) ChatHistory(ctx context.Context, chatID string, f *Filter) ([]*Message, error) {matchStage := bson.D{primitive.E{Key: "$match",Value: bson.D{primitive.E{Key: "$expr", Value: bson.D{primitive.E{Key: "$and", Value: bson.A{bson.D{primitive.E{Key: "$lte", Value: bson.D{primitive.E{Key: "$create_date",Value: f.Date, // int64},}},},}},}},},},}sortStage := bson.D{{Key: "$sort", Value: bson.D{primitive.E{Key: "create_date", Value: -1},},},}limitStage := bson.D{primitive.E{Key: "$limit", Value: f.Count}}cursor, err := r.colMessage.Aggregate(ctx, mongo.Pipeline{matchStage, sortStage, limitStage})if err != nil {l.Error().Err(err).Msg("failed find")return nil, err}var res []*Messageif err = cursor.All(ctx, &res); err != nil {l.Error().Err(err).Msg("failed find all documents")return nil, err}if err = cursor.Close(ctx); err != nil {l.Error().Err(err).Msg("failed close cursor")return nil, err}return res, nil}
Error: (InvalidPipelineOperator) Unrecognized expression '$create_date'
答案1
得分: 2
$lte的值必须是一个数组而不是一个文档：
matchStage := bson.D{primitive.E{Key: "$match",Value: bson.D{primitive.E{Key: "$expr", Value: bson.D{primitive.E{Key: "$and", Value: bson.A{bson.D{primitive.E{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
另外请注意，你可以从复合字面量中省略primitive.E类型：
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "$expr", Value: bson.D{{Key: "$and", Value: bson.A{bson.D{{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
但请注意，你在Mongo Playground上的表达式是不正确的。引用自文档：
在使用$expr时，你必须使用$eq，例如：
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "$expr", Value: bson.D{{Key: "$and", Value: bson.A{bson.D{{Key: "$eq", Value: bson.A{"$chat_id",chatID,}},},bson.D{{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
在这里尝试：https://mongoplayground.net/p/SBEJD-Fyhjl
你应该在$match中使用一个普通的查询文档。
看看这个等效的、更简单的解决方案：
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "chat_id", Value: chatID},{Key: "create_date", Value: bson.D{{Key: "$lte",Value: f.Date, // int64}},},},},}
如果你使用bson.M而不是bson.D，甚至更简单：
matchStage := bson.M{"$match": bson.M{"chat_id": chatID,"create_date": bson.M{"$lte": f.Date},},}
当然，在这种情况下，你不能使用mongo.Pipeline作为管道，但[]any或[]bson.M也可以。
英文:
Value of $lte must be an array not a document:
matchStage := bson.D{primitive.E{Key: "$match",Value: bson.D{primitive.E{Key: "$expr", Value: bson.D{primitive.E{Key: "$and", Value: bson.A{bson.D{primitive.E{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
Also note that you can leave out the primitive.E type from the composite literal:
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "$expr", Value: bson.D{{Key: "$and", Value: bson.A{bson.D{{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
But note that your expression on the mongo playground is incorrect. Quoting from the doc:
> $match takes a document that specifies the query conditions. The query syntax is identical to the read operation query syntax
...
When using $expr, you have to use $eq, for example:
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "$expr", Value: bson.D{{Key: "$and", Value: bson.A{bson.D{{Key: "$eq", Value: bson.A{"$chat_id",chatID,}},},bson.D{{Key: "$lte", Value: bson.A{"$create_date",f.Date, // int64}},},}},}},},},}
Try it here: https://mongoplayground.net/p/SBEJD-Fyhjl
You should use a normal query document in $match.
See this equivalent, much simpler solution:
matchStage := bson.D{{Key: "$match",Value: bson.D{{Key: "chat_id", Value: chatID},{Key: "create_date", Value: bson.D{{Key: "$lte",Value: f.Date, // int64}},},},},}
And even much-much simpler if you use bson.M instead of bson.D:
matchStage := bson.M{"$match": bson.M{"chat_id": chatID,"create_date": bson.M{"$lte": f.Date},},}
Of course in this last case you can't use mongo.Pipeline for the pipeline, but []any or []bson.M would also do.
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