Давайте сделаем это
Нам нужно обновить агрегацию, чтобы она заработала.
Ошибки:
users _id is ObjectId типа, но в вашем сообщении вы сохранили как String, поэтому $lookup следует изменить на Некоррелированные подзапросы - Мы заменили
$group на '$ addFields' который подходит лучше - Мы добавили в качестве последнего этапа оператор
$project, чтобы исключить все незанятые поля.
db.post.aggregate([
{
$match: {}
},
{
$lookup: {
from: "users",
let: {
postedBy: "$postedBy"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
{
"$toString": "$_id"
},
"$$postedBy"
]
}
}
}
],
as: "user"
}
},
{
$unwind: "$user"
},
{
$addFields: {
id: {
$toString: "$_id"
},
username: "$user.name",
upvotes: {
$size: "$upvotesBy"
},
isUpvoted: {
$in: [
"5e18b4c12753608718dfa007",
"$upvotesBy"
]
},
isPinned: {
$cond: [
{
$gte: [
{
$size: "$upvotesBy"
},
3
]
},
true,
false
]
},
createdAt: {
$dateToString: {
format: "%H:%M %d-%m-%Y",
timezone: "+01",
date: "$createdAt"
}
}
}
},
{
$sort: {
"isPinned": -1,
"createdAt": -1
}
},
{
$project: {
_id: 0,
user: 0,
upvotesBy: 0,
_class: 0
}
}
])
Теперь мы преобразуем этот запрос в синтаксис Spring-Data ,
Java Реализация
package postman;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.match;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.project;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.sort;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.unwind;
import java.util.Arrays;
import java.util.List;
import org.bson.Document;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Sort.Direction;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.aggregation.AggregationOperation;
import org.springframework.data.mongodb.core.aggregation.AggregationOperationContext;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.stereotype.Service;
@Service
public class PostmanService {
@Autowired
private MongoTemplate mongoTemplate;
public List<PostSummary> find(String userId){
Aggregation aggregation = Aggregation.newAggregation(
match(new Criteria()),
//lookup("users", "postedBy", "_id", "user")
new AggregationOperation() {
@Override
public Document toDocument(AggregationOperationContext context) {
return new Document("$lookup",
new Document("from", "users")
.append("let", new Document("postedBy", "$postedBy"))
.append("pipeline", Arrays.asList(
new Document("$match",
new Document("$expr",
new Document("$eq", Arrays.asList(
new Document("$toString", "$_id"),
"$$postedBy"
))))))
.append("as", "user"));
}
},
unwind("$user"),
new AggregationOperation() {
@Override
public Document toDocument(AggregationOperationContext context) {
return new Document("$addFields",
new Document("id", new Document("$toString", "$_id"))
.append("username", "$user.name")
.append("upvotes", new Document("$size", "$upvotesBy"))
.append("isUpvoted", new Document("$in", Arrays.asList(userId, "$upvotesBy")))
.append("isPinned", new Document("$cond",
Arrays.asList(new Document("$gte",
Arrays.asList(new Document("$size", "$upvotesBy"), 3)), Boolean.TRUE, Boolean.FALSE)))
.append("createdAt", new Document("$dateToString",
new Document("format", "%H:%M %d-%m-%Y")
.append("timezone", "+01")
.append("date", "$createdAt")
)));
}
},
sort(Direction.DESC, "isPinned", "createdAt"),
project().andExclude("user", "_class")
);
System.out.println("Aggregation: " + aggregation.toString());
return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(Post.class), PostSummary.class).getMappedResults();
}
}
Теперь мы вызываем конвейер агрегации:
List<PostSummary> l = postmanService.find("5e18b4c12753608718dfa007");
for(PostSummary post: l) {
ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
System.out.println(ow.writeValueAsString(post));
}
2020-01-12 16:15:22.043 INFO 11148 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2020-01-12 16:15:22.047 INFO 11148 --- [ main] Postman.PostmanApplication : Started PostmanApplication in 4.602 seconds (JVM running for 5.301)
Aggregation: { "aggregate" : "__collection__", "pipeline" : [{ "$match" : {}}, { "$lookup" : { "from" : "users", "let" : { "postedBy" : "$postedBy"}, "pipeline" : [{ "$match" : { "$expr" : { "$eq" : [{ "$toString" : "$_id"}, "$$postedBy"]}}}], "as" : "user"}}, { "$unwind" : "$user"}, { "$addFields" : { "id" : { "$toString" : "$_id"}, "username" : "$user.name", "upvotes" : { "$size" : "$upvotesBy"}, "isUpvoted" : { "$in" : ["5e18b4c12753608718dfa007", "$upvotesBy"]}, "isPinned" : { "$cond" : [{ "$gte" : [{ "$size" : "$upvotesBy"}, 3]}, true, false]}, "createdAt" : { "$dateToString" : { "format" : "%H:%M %d-%m-%Y", "timezone" : "+01", "date" : "$createdAt"}}}}, { "$sort" : { "isPinned" : -1, "createdAt" : -1}}, { "$project" : { "user" : 0, "_class" : 0}}]}
2020-01-12 16:15:22.161 INFO 11148 --- [ main] org.mongodb.driver.connection : Opened connection [connectionId{localValue:2, serverValue:277}] to localhost:27017
{
"username" : "user1",
"title" : "postim2",
"description" : "description2",
"upvotesBy" : [ "5e18b4c12753608718dfa007", "5e19ac0f5161a4994ded1f35" ],
"file" : "test2",
"createdAt" : "10:46 12-01-2020",
"id" : "5e1aeaf8275360bb4bb47325"
}
{
"username" : "user1",
"title" : "postim",
"description" : "description",
"upvotesBy" : [ "5e18b4c12753608718dfa007", "5e19ac0f5161a4994ded1f35" ],
"file" : "test",
"createdAt" : "10:44 12-01-2020",
"id" : "5e1aea6c275360baf96bac29"
}