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multi collection querying using aggregation pipeline implemented by go
// import (
// "fmt"
// "time"
//
// mgo "gopkg.in/mgo.v2"
// "gopkg.in/mgo.v2/bson"
// )
// ``` cmd in mongo shell
// db.Slot.aggregate([
// {$lookup:
// {
// from: "SlotOrder",
// localField: "_id",
// foreignField: "SlotId",
// as: "SO"
// }
// },
// {$unwind:"$SO"},
// {$lookup:
// {
// from: "Order",
// localField: "SO.OrderId",
// foreignField: "_id",
// as: "Order"
// }
// },
// {$unwind:"$Order"},
// {$project:{_id:1,Order:1,OrderStat:{$cond:[{$lt:["$Order.Begin",now]},
// scheduled,
// $cond:[{$eq:["$Order.End",0]},
// busy,
// $cond:[{$lte:["$Order.End",now]},busy,idle]]}}},
// {$match:{"OrderStat":{$eq:statYouNeed}}},
// {$group:
// {
// "_id":"$_id",
// "Order":{"$AddToSet":"$Order"},
// "OrderStat":{"$AddToSet":"$OrderStat"},
// }
// },
// ])
// ```
func MergeBson(basic, addOn bson.M) bson.M {
if len(addOn) < 1 {
return basic
}
for k, v := range addOn {
basic[k] = v
}
return basic
}
func MultiCollectionQueryDemo() {
println("//<<-------------------------MultiCollectionQueryDemo start-----------")
start := time.Now()
const (
DB = "youdb"
COLLECTION = "you-collection"
)
session, err := mgo.Dial(ADDRESSPORT)
if err != nil {
return
}
defer session.Close()
c := session.DB(DB).C(COLLECTION)
basicCollumns := bson.M{"Name": true}
const (
_id = "_id"
middleSO = "slotOrder"
SlotState = "SlotState"
)
const (
SlotStateFree = iota // order associated
SlotStateIdle
SlotStateBusy
SlotStateSchedule
)
var slotStatList = []int{SlotStateBusy, SlotStateIdle, SlotStateSchedule}
lookSO := bson.M{
"$lookup": bson.M{"from": "AdSlotOrder", "localField": "_id", "foreignField": "AdSlotId", "as": middleSO},
}
handlerSO := bson.M{
"$project": MergeBson(bson.M{
_id: true,
SlotState: bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$" + middleSO, []bson.M{}}}, SlotStateIdle, SlotStateFree}},
middleSO: bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$" + middleSO, []bson.M{}}}, 0, "$" + middleSO}},
}, basicCollumns),
}
splitSO := bson.M{
"$unwind": "$" + middleSO,
}
lookOrder := bson.M{
"$lookup": bson.M{"from": "Order", "localField": middleSO + ".OrderId", "foreignField": _id, "as": "Order"},
}
handlerOrder := bson.M{
"$project": MergeBson(bson.M{
_id: true,
SlotState: true,
"Order": bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$Order", []bson.M{}}}, 0, "$Order"}},
}, basicCollumns),
}
splitOrder := bson.M{
"$unwind": "$Order",
}
const currentTime = 1447948100
handlerSlotState := bson.M{
"$project": MergeBson(bson.M{
_id: true,
"Order": true,
SlotState: bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$" + SlotState, SlotStateIdle}}, SlotStateIdle,
bson.M{"$cond": []interface{}{bson.M{"$lt": []interface{}{"$Order.Begin", currentTime}}, SlotStateSchedule,
//0 means no dealine for order
bson.M{"$cond": []interface{}{bson.M{"$eq": []interface{}{"$Order.End", 0}}, SlotStateBusy,
bson.M{"$cond": []interface{}{bson.M{"$lte": []interface{}{"$Order.End", currentTime}}, SlotStateIdle, SlotStateBusy}}}}}}}},
}, basicCollumns),
}
filterState := bson.M{
"$match": bson.M{SlotState: bson.M{"$in": slotStatList}},
}
groupResult := bson.M{
"$group": bson.M{
_id: "$" + _id,
"Name": bson.M{"$first": "$Name"},
"Order": bson.M{"$addToSet": ("$Order")},
SlotState: bson.M{"$addToSet": ("$" + SlotState)},
}}
operations := []bson.M{lookSO, handlerSO, splitSO, lookOrder, splitOrder, handlerOrder, handlerSlotState, filterState, groupResult}
ret := []interface{}{}
pipe := c.Pipe(operations)
err = pipe.All(&ret)
if err != nil {
panic(err.Error())
return
}
for k, v := range ret {
fmt.Printf("%+v: %+v\n", k, v)
}
fmt.Printf("MultiCollectionQueryDemo costs %d millisecons actually %v\n", time.Since(start).Nanoseconds()/1000000, time.Since(start))
println("//---------------------------MultiCollectionQueryDemo end----------->>")
}
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