对于MongoDB 3.6及更高版本,请使用100运算符,该运算符允许在查询语言中使用聚合表达式:
var followers_count = 30;
db.locations.find({
"$expr": {
"$and": [
{ "$eq": ["$name", "development"] },
{ "$gte": [{ "$size": "$followers" }, followers_count ]}
]
}
});
对于不兼容的版本,可以使用100和101管道来查询集合.例如,如果要查询名称为"development"且followers_count
大于30的locations
集合,请运行以下聚合操作:
const followers_count = 30;
Locations.aggregate([
{ "$match": { "name": "development" } },
{
"$redact": {
"$cond": [
{ "$gte": [ { "$size": "$followers" }, followers_count ] },
"$$KEEP",
"$$PRUNE"
]
}
}
]).exec((err, locations) => {
if (err) throw err;
console.log(locations);
})
或者在单个管道内
Locations.aggregate([
{
"$redact": {
"$cond": [
{
"$and": [
{ "$eq": ["$name", "development"] },
{ "$gte": [ { "$size": "$followers" }, followers_count ] }
]
},
"$$KEEP",
"$$PRUNE"
]
}
}
]).exec((err, locations) => {
if (err) throw err;
console.log(locations);
})
上面的内容只会返回用户提供的_id
条参考信息.要将用户文档作为"填充"关注者数组的手段返回,可以附加100管道.
如果基础Mongo server版本为3.4及更高版本,则可以按以下方式运行管道:
let followers_count = 30;
Locations.aggregate([
{ "$match": { "name": "development" } },
{
"$redact": {
"$cond": [
{ "$gte": [ { "$size": "$followers" }, followers_count ] },
"$$KEEP",
"$$PRUNE"
]
}
},
{
"$lookup": {
"from": "users",
"localField": "followers",
"foreignField": "_id",
"as": "followers"
}
}
]).exec((err, locations) => {
if (err) throw err;
console.log(locations);
})
否则,在应用101之前,您需要使用100跟随者数组,然后使用102管道重新组合:
let followers_count = 30;
Locations.aggregate([
{ "$match": { "name": "development" } },
{
"$redact": {
"$cond": [
{ "$gte": [ { "$size": "$followers" }, followers_count ] },
"$$KEEP",
"$$PRUNE"
]
}
},
{ "$unwind": "$followers" },
{
"$lookup": {
"from": "users",
"localField": "followers",
"foreignField": "_id",
"as": "follower"
}
},
{ "$unwind": "$follower" },
{
"$group": {
"_id": "$_id",
"created": { "$first": "$created" },
"name": { "$first": "$name" },
"followers": { "$push": "$follower" }
}
}
]).exec((err, locations) => {
if (err) throw err;
console.log(locations);
})