I'm trying to do the following, get a list of chats from the chat collection of a particular user, and add to that list for each chat the last message from the message collection that was sent.
How this works now, I have two methods, they are described below
First I just get a list of chats using the chat member id, and the second method uses aggregation to look for the last message for each chat, then I just match the messages with the id of the chat
collection chat:
type Chat struct {
ID string `json:"id" bson:"id"`
Participants []string `json:"participants" bson:"participants"`
LastMessage *Message `json:"last_message,omitempty" bson:"last_message"`
...
}
P.S.
LastMessage - is always nil, I only need it to compose the response for the user.
Collection message:
type Message struct {
ID string `json:"id" bson:"id"`
ChatID string `json:"chat_id" bson:"chat_id"`
FromID string `json:"from_id" bson:"from_id"`
CreateDate int64 `json:"create_date" bson:"create_date"`
Body string `json:"body" bson:"body"`
UpdateAt int64 `json:"update_at" bson:"update_at"`
...
}
First method: I need this method to get a list of active chats of a particular chat participant.
func ActiveChats(ctx context.Context, uid string) ([]*Chat, error) {
...
filter := bson.D{primitive.E{Key: "participants", Value: uid}}
cursor, err := r.col.Find(ctx, filter, nil)
if err != nil {...}
var ch []*chat
if err = cursor.All(ctx, &ch); err != nil {...}
if err = cursor.Close(ctx); err != nil {...}
...
}
Second method: I need this method to get the last message for each chat, the input is an array of chat IDs, and for each I search for the last message if there is one. To do this I use aggregation.
func LastMessages(ctx context.Context, chatIds []string) (map[string]*Message, error) {
matchStage := bson.D{
primitive.E{
Key: "$match", Value: bson.D{
primitive.E{
Key: "chat_id", Value: bson.D{
primitive.E{Key: "$in", Value: chatIds},
},
},
},
}}
sortStage := bson.D{primitive.E{Key: "$sort", Value: bson.D{primitive.E{Key: "created", Value: -1}}}}
groupStage := bson.D{primitive.E{
Key: "$group", Value: bson.D{
primitive.E{
Key: "_id", Value: bson.D{
primitive.E{Key: "chat_id", Value: "$chat_id"},
},
},
primitive.E{
Key: "message", Value: bson.D{
primitive.E{Key: "$first", Value: "$$ROOT"},
},
},
},
}}
cursor, err := r.colMessage.Aggregate(ctx, mongo.Pipeline{matchStage, groupStage, sortStage})
if err != nil {...}
var res []*aggregationResultGenerated
if err = cursor.All(ctx, &res); err != nil {...}
...
}
I know it's a very bad solution, but it's all I've been able to come up with so far, much to my regret(not workig). I try fix this
db.chat.aggregate([
{
$match: {
participants: "participant_id",
},
{
$lookup: {
from: "message", // other table name
localField: "id", // name of chat table field
foreignField: "chat_id", // name of message table field
as: "msg",
}
},
{
$unwind: "$msg",
},
{
$match: {
chat_id : {
$in: ["$$ROOT._id"],
},
},
},
{
$sort: {
"created": -1,
},
},
{
$group: {
"_id": {
"chat_id": "$chat_id"
},
"doc": {
"$last": "$$ROOT"
}
}
},
{
$project: {
last_message: "$msg",
}
}
])
My question is: How can I use aggregation to get a list of chats of a particular user, and for each chat add from the collection message the last message in the field last_message in the object chat?
How it works now:
{
"chats": [
{
"id": "4hWsHam3ZZpoyIw44q3D",
"title": "Chat example",
"create-date": 1674476855918,
"participants": [
"63ce54460aeee5e72c778d90",
"63ce54460aeee5e72c778d92"
],
"owner_id": "63ce54460aeee5e72c778d90",
"last_message": {
"id": "tzwekCiCLSXJ4tfdQuHH",
"chat_id": "4hWsHam3ZZpoyIw44q3D",
"from_id": "63ce54460aeee5e72c778d92",
"create_date": 1674557062031,
"body": "text",
"update_at": 0,
"viewed": false
},
"unread": 5
},
{
"id": "Anjrr9RCWFzq030Cwz7S",
"title": "New chat One",
"create-date": 1674476909054,
"participants": [
"63ce54460aeee5e72c778d90",
"63ce54460aeee5e72c778d96"
],
"owner_id": "63ce54460aeee5e72c778d90",
"last_message": {
"id": "7YqhhS1-EfMRSZtGCH0Z",
"chat_id": "Anjrr9RCWFzq030Cwz7S",
"from_id": "63ce54460aeee5e72c778d96",
"create_date": 1674575017115,
"body": "text",
"update_at": 0,
},
"unread": 1
},
]
}
CodePudding user response：
Edit: As mentioned by OP in the comment, update/$merge to collection is not necessary.
You can simply do a $sort $limit approach in the sub-pipeline of a $lookup. Do a $unwind to wrangle the lookup result to the last_message field. Finally, do a $merge to update back to the chat collection.
db.chat.aggregate([
{
$match: {
participants: "63ce54460aeee5e72c778d90",
}
},
{
$lookup: {
from: "message",
localField: "id",
foreignField: "chat_id",
pipeline: [
{
$sort: {
created: -1
}
},
{
$limit: 1
}
],
as: "last_message",
}
},
{
$unwind: {
path: "$last_message",
preserveNullAndEmptyArrays: true
}
},
{
$project: {
last_message: "$last_message"
}
}
])
Here is an old Mongo Playground with $merge to update to a collection.