DATAMONGO-2001 - Count within transaction should return only the total count of documents visible to the specific session.
We now delegate count operations within an active transaction to an aggregation.
Once `MongoTemplate` detects an active transaction, all exposed `count()` methods are converted and delegated to the
aggregation framework using `$match` and `$count` operators, preserving `Query` settings, such as `collation`.
The following snippet of `count` inside the session bound closure
session.startTransaction();
template.withSession(session)
.execute(action -> {
action.count(query(where("state").is("active")), Step.class)
...
runs:
db.collection.aggregate(
[
{ $match: { state: "active" } },
{ $count: "totalEntityCount" }
]
)
instead of:
db.collection.find( { state: "active" } ).count()
Original pull request: #568.
This commit is contained in:
Christoph Strobl
committed by
Mark Paluch
Mark Paluch
parent
8145b84dbe
commit
05f325687c
@@ -127,7 +127,6 @@ template.withSession(session)
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session.abortTransaction(); <4>
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}
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}, ClientSession::close) <5>
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.subscribe();
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----
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<1> Obtain a new `ClientSession`.
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<2> Start the transaction.
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@@ -155,16 +154,16 @@ TransactionTemplate txTemplate = new TransactionTemplate(anyTxManager);
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txTemplate.execute(new TransactionCallbackWithoutResult() {
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@Override
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protected void doInTransactionWithoutResult(TransactionStatus status) { <3>
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@Override
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protected void doInTransactionWithoutResult(TransactionStatus status) { <3>
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Step step = // ...;
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template.insert(step);
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Step step = // ...;
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template.insert(step);
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process(step);
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process(step);
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template.update(Step.class).apply(Update.set("state", // ...
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};
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template.update(Step.class).apply(Update.set("state", // ...
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};
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});
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----
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<1> Enable transaction synchronization during Template API configuration.
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@@ -186,26 +185,26 @@ The `MongoTransactionManager` binds a `ClientSession` to the thread. `MongoTempl
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@Configuration
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static class Config extends AbstractMongoConfiguration {
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@Bean
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MongoTransactionManager transactionManager(MongoDbFactory dbFactory) { <1>
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return new MongoTransactionManager(dbFactory);
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}
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@Bean
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MongoTransactionManager transactionManager(MongoDbFactory dbFactory) { <1>
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return new MongoTransactionManager(dbFactory);
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}
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// ...
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// ...
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}
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@Component
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public class StateService {
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@Transactional
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void someBusinessFunction(Step step) { <2>
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@Transactional
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void someBusinessFunction(Step step) { <2>
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template.insert(step);
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template.insert(step);
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process(step);
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process(step);
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template.update(Step.class).apply(Update.set("state", // ...
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};
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template.update(Step.class).apply(Update.set("state", // ...
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};
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});
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----
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@@ -230,18 +229,18 @@ Using the plain MongoDB reactive driver API a `delete` within a transactional fl
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[source,java]
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----
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Mono<DeleteResult> result = Mono
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.from(client.startSession()) <1>
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.from(client.startSession()) <1>
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.flatMap(session -> {
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session.startTransaction(); <2>
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.flatMap(session -> {
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session.startTransaction(); <2>
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return Mono.from(collection.deleteMany(session, ...)) <3>
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return Mono.from(collection.deleteMany(session, ...)) <3>
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.onErrorResume(e -> Mono.from(session.abortTransaction()).then(Mono.error(e))) <4>
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.onErrorResume(e -> Mono.from(session.abortTransaction()).then(Mono.error(e))) <4>
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.flatMap(val -> Mono.from(session.commitTransaction()).then(Mono.just(val))) <5>
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.flatMap(val -> Mono.from(session.commitTransaction()).then(Mono.just(val))) <5>
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.doFinally(signal -> session.close()); <6>
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.doFinally(signal -> session.close()); <6>
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});
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----
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<1> First we obviously need to initiate the session.
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@@ -263,9 +262,9 @@ accordingly. This allows you to express the above flow simply as the following:
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====
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[source,java]
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----
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Mono<DeleteResult> result = template.inTransaction() <1>
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Mono<DeleteResult> result = template.inTransaction() <1>
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.execute(action -> action.remove(query(where("id").is("step-1")), Step.class)); <2>
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.execute(action -> action.remove(query(where("id").is("step-1")), Step.class)); <2>
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----
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<1> Initiate the transaction.
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<2> Operate within the `ClientSession`. Each `execute(…)` unit of work callback initiates a new transaction in the scope of the same `ClientSession`.
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@@ -280,20 +279,77 @@ reactive flow of `execute(…)` that are not propagated to outside of the callba
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====
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[source,java]
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----
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template.inTransaction() <1>
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template.inTransaction() <1>
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.execute(action -> action.find(query(where("state").is("active")), Step.class)
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.flatMap(step -> action.update(Step.class)
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.matching(query(where("id").is(step.id)))
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.apply(update("state", "paused"))
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.all())) <2>
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.execute(action -> action.find(query(where("state").is("active")), Step.class)
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.flatMap(step -> action.update(Step.class)
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.matching(query(where("id").is(step.id)))
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.apply(update("state", "paused"))
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.all())) <2>
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.flatMap(updated -> {
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// Exception could happen here <3>
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});
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.flatMap(updated -> {
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// Exception could happen here <3>
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});
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----
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<1> Initiate the managed transaction.
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<2> Operate within the `ClientSession`. The transaction is committed after this is done or rolled back if an
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error occurs here.
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<3> An error outside the transaction flow has no affect on the previous transactional execution.
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====
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== Special behavior inside transactions
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Inside transactions MongoDB server has a slightly different behavior.
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*Connection Settings*
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The MongoDB drivers offer a dedicated replica set name configuration option turing the driver into an auto detection
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mode. This option helps identifying replica set master nodes and command routing during a transaction.
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INFO: Make sure to add `replicaSet` to the MongoDB Uri. Please refer to https://docs.mongodb.com/manual/reference/connection-string/#connections-connection-options[connection string options] for further details.
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*Collection Operations*
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MongoDB does *not* support collection operations, such as collection creation, within a transaction. This also
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affects the on the fly collection creation that happens on first usage. Therefore make sure to have all required
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structures in place.
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*Count*
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MongoDB `count` operates upon collection statistics which may not reflect the actual situation within a transaction.
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The server responds with _error 50851_ when issuing a `count` command inside of a multi-document transaction.
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Once `MongoTemplate` detects an active transaction, all exposed `count()` methods are converted and delegated to the
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aggregation framework using `$match` and `$count` operators, preserving `Query` settings, such as `collation`.
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====
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The following snippet of `count` inside the session bound closure
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[source,javascript]
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----
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session.startTransaction();
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template.withSession(session)
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.execute(action -> {
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action.count(query(where("state").is("active")), Step.class)
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...
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----
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runs:
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[source,javascript]
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----
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db.collection.aggregate(
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[
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{ $match: { state: "active" } },
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{ $group: { _id: null, count: { $sum: 1 } } }
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]
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)
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----
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instead of:
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[source,javascript]
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----
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db.collection.find( { state: "active" } ).count()
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----
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====
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