如何将 mongodb 投影与 Go 和 mgo 一起使用?
How can I use mongodb projections with Go and mgo?
我目前正在尝试在 mongodb 的文档数组中提取单个对象。
这是一个示例数据集:
"_id" : ObjectId("564aae61e0c4e5dddb07343b"),
"name" : "The Races",
"description" : "Horse races",
"capacity" : 0,
"open" : true,
"type" : 0,
"races" : [
{
"_id" : ObjectId("564ab9097628ba2c6ec54423"),
"race" : {
"distance" : 3000,
"user" : {
"_id" : ObjectId("5648bdbe7628ba189e011b18"),
"status" : 1,
"lastName" : "Miranda",
"firstName" : "Aramys"
}
}
},
{
"_id" : ObjectId("564ab9847628ba2c81f2f34a"),
"bet" : {
"distance" : 3000,
"user" : {
"_id" : ObjectId("5648bdbe7628ba189e011b18"),
"status" : 1,
"lastName" : "Miranda",
"firstName" : "Aramys"
}
}
},{...}
]
我可以在 mongo 中使用以下命令成功查询:
db.tracks.find({"_id": ObjectId("564aae61e0c4e5dddb07343b")}, {"races": { $elemMatch: {"_id": ObjectId("564ab9847628ba2c81f2f34a")}}}).pretty()
我无法使用 mgo 做同样的事情并尝试了以下方法:
使用嵌套(抛出:复合文字中缺少类型,地图文字中缺少键)
// Using nesting (Throws: missing type in composite literal, missing key in map literal)
c.Find(bson.M{{"_id": bson.ObjectIdHex(p.ByName("id"))}, bson.M{"races": bson.M{"$elemMatch": bson.M{"_id": bson.ObjectIdHex(p.ByName("raceId"))}}}}).One(&result)
// Using select (Returns empty)
c.Find(bson.M{"_id": bson.ObjectIdHex(p.ByName("id"))}).Select(bson.M{"races._id": bson.ObjectIdHex(p.ByName("raceId"))}).One(&result)
//As an array (Returns empty)
c.Find([]bson.M{{"_id": bson.ObjectIdHex(p.ByName("id"))}, bson.M{"races": bson.M{"$elemMatch": bson.M{"_id": bson.ObjectIdHex(p.ByName("raceId"))}}}}).One(&result)
我正在使用 httprouter,p.ByName("...") 调用是传递给处理程序的参数。
提前致谢。
将使用 Select
method as the doc states that this enables selecting which fields should be retrieved for the results found, thus the projection using $elemMatch
operator can be applied here in conjuction with Select
,您的最终查询类似于:
c.Find(bson.M{
"_id": bson.ObjectIdHex(p.ByName("id"))
}).Select(bson.M{
"races": bson.M{
"$elemMatch": bson.M{
"_id": bson.ObjectIdHex(p.ByName("raceId"))
}
}
}).One(&result)
我目前正在尝试在 mongodb 的文档数组中提取单个对象。 这是一个示例数据集:
"_id" : ObjectId("564aae61e0c4e5dddb07343b"),
"name" : "The Races",
"description" : "Horse races",
"capacity" : 0,
"open" : true,
"type" : 0,
"races" : [
{
"_id" : ObjectId("564ab9097628ba2c6ec54423"),
"race" : {
"distance" : 3000,
"user" : {
"_id" : ObjectId("5648bdbe7628ba189e011b18"),
"status" : 1,
"lastName" : "Miranda",
"firstName" : "Aramys"
}
}
},
{
"_id" : ObjectId("564ab9847628ba2c81f2f34a"),
"bet" : {
"distance" : 3000,
"user" : {
"_id" : ObjectId("5648bdbe7628ba189e011b18"),
"status" : 1,
"lastName" : "Miranda",
"firstName" : "Aramys"
}
}
},{...}
]
我可以在 mongo 中使用以下命令成功查询:
db.tracks.find({"_id": ObjectId("564aae61e0c4e5dddb07343b")}, {"races": { $elemMatch: {"_id": ObjectId("564ab9847628ba2c81f2f34a")}}}).pretty()
我无法使用 mgo 做同样的事情并尝试了以下方法:
使用嵌套(抛出:复合文字中缺少类型,地图文字中缺少键)
// Using nesting (Throws: missing type in composite literal, missing key in map literal)
c.Find(bson.M{{"_id": bson.ObjectIdHex(p.ByName("id"))}, bson.M{"races": bson.M{"$elemMatch": bson.M{"_id": bson.ObjectIdHex(p.ByName("raceId"))}}}}).One(&result)
// Using select (Returns empty)
c.Find(bson.M{"_id": bson.ObjectIdHex(p.ByName("id"))}).Select(bson.M{"races._id": bson.ObjectIdHex(p.ByName("raceId"))}).One(&result)
//As an array (Returns empty)
c.Find([]bson.M{{"_id": bson.ObjectIdHex(p.ByName("id"))}, bson.M{"races": bson.M{"$elemMatch": bson.M{"_id": bson.ObjectIdHex(p.ByName("raceId"))}}}}).One(&result)
我正在使用 httprouter,p.ByName("...") 调用是传递给处理程序的参数。
提前致谢。
将使用 Select
method as the doc states that this enables selecting which fields should be retrieved for the results found, thus the projection using $elemMatch
operator can be applied here in conjuction with Select
,您的最终查询类似于:
c.Find(bson.M{
"_id": bson.ObjectIdHex(p.ByName("id"))
}).Select(bson.M{
"races": bson.M{
"$elemMatch": bson.M{
"_id": bson.ObjectIdHex(p.ByName("raceId"))
}
}
}).One(&result)