mongodb - MongoDB管道中的多个顶级聚合查询

Question

我有以下查询:

match := bson.D{{"$match", bson.D{{"venue", venueID}}}}
group := bson.D{{"$lookup", bson.M{
    "from":         "labels",
    "localField":   "label_ids",
    "foreignField": "_id",
    "as":           "labels",
}}, {"$graphLookup", bson.M{
    "from":             "menus",
    "startWith":        "$child_ids",
    "connectFromField": "child_ids",
    "connectToField":   "_id",
    "as":               "children",
    "maxDepth":         5,
    "depthField":       "level",
}}}

cur, err := m.collection.Aggregate(ctx, mongo.Pipeline{group, match})

我有两个相关的字段，其中一个是图形结构(菜单)，每个父元素都有一个ID数组，用于每个子元素。
第二个字段，标签，只是一对多的查询。标签和菜单应该是可重用的，因此不能嵌入单个父实体中。上面概述的查询对我来说很有意义，但是出现以下错误: A pipeline stage specification object must contain exactly one field.谢谢!

Answer 1

MongoDB管道中的每个元素都必须是单个阶段，例如$match，$group等
您的group元素包含两个阶段:$lookup和$graphLookup。
拆分它们并单独列出:

match := bson.D{{"$match", bson.D{{"venue", venueID}}}}
group := bson.D{{"$lookup", bson.M{
    "from":         "labels",
    "localField":   "label_ids",
    "foreignField": "_id",
    "as":           "labels",
}}}
graphLookup := bson.D{{"$graphLookup", bson.M{
    "from":             "menus",
    "startWith":        "$child_ids",
    "connectFromField": "child_ids",
    "connectToField":   "_id",
    "as":               "children",
    "maxDepth":         5,
    "depthField":       "level",
}}}

cur, err := m.collection.Aggregate(ctx, mongo.Pipeline{group, graphLookup, match})