{
"_id" : {
"$oid" : "5b8e1d485d30a6499820cfc5"
},
"id" : 5,
"lessonCount" : 5,
"userCount" : 6,
"users" : [{
"phone" : "1301111000",
"liveCount" : 0,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 0,
"id" : 2
}, {
"time" : 0,
"id" : 3
}, {
"time" : 0,
"id" : 4
}, {
"time" : 0,
"id" : 5
}]
}, {
"phone" : "1301111001",
"liveCount" : 1,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 1,
"id" : 2
}, {
"time" : 2,
"id" : 3
}, {
"time" : 3,
"id" : 4
}, {
"time" : 4,
"id" : 5
}]
}, {
"phone" : "1301111002",
"liveCount" : 2,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 2,
"id" : 2
}, {
"time" : 4,
"id" : 3
}, {
"time" : 6,
"id" : 4
}, {
"time" : 8,
"id" : 5
}]
}, {
"phone" : "1301111003",
"liveCount" : 3,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 3,
"id" : 2
}, {
"time" : 6,
"id" : 3
}, {
"time" : 9,
"id" : 4
}, {
"time" : 12,
"id" : 5
}]
}, {
"phone" : "1301111004",
"liveCount" : 4,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 4,
"id" : 2
}, {
"time" : 8,
"id" : 3
}, {
"time" : 12,
"id" : 4
}, {
"time" : 16,
"id" : 5
}]
}, {
"phone" : "1301111005",
"liveCount" : 5,
"learns" : [{
"time" : 0,
"id" : 1
}, {
"time" : 5,
"id" : 2
}, {
"time" : 10,
"id" : 3
}, {
"time" : 15,
"id" : 4
}, {
"time" : 20,
"id" : 5
}]
}]
}- now you need to page users and learns under users at the same time. Here is the Java code
public void queryAggregates() {
List<Bson> bsons = new ArrayList<>();
Bson id = Aggregates.match(Filters.eq("id", 5));
Bson match = Aggregates.match(Filters.eq("users.learns.id", 3));
Bson unwind = Aggregates.unwind("$users");
Bson match2 = Aggregates.match(Filters.eq("users.learns.id", 3));
Bson sort = Aggregates.sort(Sorts.descending("users.learns.time"));
Bson limit = Aggregates.limit(5);
Bson project = Aggregates.project(Projections.slice("users.learns", 2,3));
bsons.add(id);
bsons.add(match);
bsons.add(unwind);
bsons.add(match2);
bsons.add(sort);
bsons.add(limit);
bsons.add(project);
AggregateIterable<Document> aggregate = c.aggregate(bsons);
for (Document document : aggregate) {
Object users = document.get("users");
System.out.println(users);
}
}will report the following error
com.mongodb.MongoCommandException: Command failed with error 28724 (Location28724): "First argument to $slice must be an array, but is of type: int" on server 127.0.0.1:27017. The full response is { "ok" : 0.0, "errmsg" : "First argument to $slice must be an array, but is of type: int", "code" : 28724, "codeName" : "Location28724" }
at com.mongodb.internal.connection.ProtocolHelper.getCommandFailureException(ProtocolHelper.java:179)
at com.mongodb.internal.connection.InternalStreamConnection.receiveCommandMessageResponse(InternalStreamConnection.java:293)
at com.mongodb.internal.connection.InternalStreamConnection.sendAndReceive(InternalStreamConnection.java:255)
at com.mongodb.internal.connection.UsageTrackingInternalConnection.sendAndReceive(UsageTrackingInternalConnection.java:99)
at com.mongodb.internal.connection.DefaultConnectionPool$PooledConnection.sendAndReceive(DefaultConnectionPool.java:444)
at com.mongodb.internal.connection.CommandProtocolImpl.execute(CommandProtocolImpl.java:72)
at com.mongodb.internal.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:200)
at com.mongodb.internal.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:269)
at com.mongodb.internal.connection.DefaultServerConnection.command(DefaultServerConnection.java:131)
at com.mongodb.internal.connection.DefaultServerConnection.command(DefaultServerConnection.java:123)
at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:242)
at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:233)
at com.mongodb.operation.CommandOperationHelper.executeWrappedCommandProtocol(CommandOperationHelper.java:136)
at com.mongodb.operation.AggregateOperationImpl$1.call(AggregateOperationImpl.java:193)
at com.mongodb.operation.AggregateOperationImpl$1.call(AggregateOperationImpl.java:189)
at com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:457)
at com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:401)
at com.mongodb.operation.AggregateOperationImpl.execute(AggregateOperationImpl.java:189)
at com.mongodb.operation.AggregateOperation.execute(AggregateOperation.java:294)
at com.mongodb.operation.AggregateOperation.execute(AggregateOperation.java:41)
at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:179)
at com.mongodb.client.internal.MongoIterableImpl.execute(MongoIterableImpl.java:132)
at com.mongodb.client.internal.MongoIterableImpl.iterator(MongoIterableImpl.java:86)
at com.lyn.mongo.TestMongo.queryAggregates(TestMongo.java:93)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70) if you do not use project to aggregate that line of code, users paging is normal, but users.learns paging cannot be implemented.
here are the query results without project aggregation
Document{{phone=1301111005, liveCount=5, learns=[Document{{time=0, id=1}}, Document{{time=5, id=2}}, Document{{time=10, id=3}}, Document{{time=15, id=4}}, Document{{time=20, id=5}}]}}
Document{{phone=1301111004, liveCount=4, learns=[Document{{time=0, id=1}}, Document{{time=4, id=2}}, Document{{time=8, id=3}}, Document{{time=12, id=4}}, Document{{time=16, id=5}}]}}
Document{{phone=1301111003, liveCount=3, learns=[Document{{time=0, id=1}}, Document{{time=3, id=2}}, Document{{time=6, id=3}}, Document{{time=9, id=4}}, Document{{time=12, id=5}}]}}
Document{{phone=1301111002, liveCount=2, learns=[Document{{time=0, id=1}}, Document{{time=2, id=2}}, Document{{time=4, id=3}}, Document{{time=6, id=4}}, Document{{time=8, id=5}}]}}
Document{{phone=1301111001, liveCount=1, learns=[Document{{time=0, id=1}}, Document{{time=1, id=2}}, Document{{time=2, id=3}}, Document{{time=3, id=4}}, Document{{time=4, id=5}}]}} Java api is 3.8.1
how to implement users.learns pagination?
I don"t know much about using mongoDB, for the first time. Please give me more advice