#517 - Add example for declarative reactive transactions in MongoDB.

Original pull request: #518.

mongodb/transactions/src/main/java/example/springdata/mongodb/reactive/ReactiveManagedTransitionService.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package example.springdata.mongodb.reactive;
+
+import example.springdata.mongodb.Process;
+import example.springdata.mongodb.State;
+import lombok.RequiredArgsConstructor;
+import reactor.core.publisher.Mono;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.springframework.data.mongodb.core.ReactiveMongoOperations;
+import org.springframework.data.mongodb.core.ReactiveMongoTemplate;
+import org.springframework.data.mongodb.core.query.Criteria;
+import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.mongodb.core.query.Update;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.util.Assert;
+
+/**
+ * @author Christoph Strobl
+ */
+@Service
+@RequiredArgsConstructor
+public class ReactiveManagedTransitionService {
+
+	final ReactiveProcessRepository repository;
+	final ReactiveMongoTemplate template;
+
+	final AtomicInteger counter = new AtomicInteger(0);
+
+	public Mono<Process> newProcess() {
+		return repository.save(new Process(counter.incrementAndGet(), State.CREATED, 0));
+	}
+
+	@Transactional
+	public Mono<Integer> run(Integer id) {
+
+		return lookup(id) //
+				.flatMap(process -> start(template, process)) //
+				.flatMap(it -> verify(it)) //
+				.flatMap(process -> finish(template, process)) //
+				.map(Process::getId);
+	}
+
+	private Mono<Process> finish(ReactiveMongoOperations operations, Process process) {
+
+		return operations.update(Process.class).matching(Query.query(Criteria.where("id").is(process.getId())))
+				.apply(Update.update("state", State.DONE).inc("transitionCount", 1)).first() //
+				.then(Mono.just(process));
+	}
+
+	Mono<Process> start(ReactiveMongoOperations operations, Process process) {
+
+		return operations.update(Process.class).matching(Query.query(Criteria.where("id").is(process.getId())))
+				.apply(Update.update("state", State.ACTIVE).inc("transitionCount", 1)).first() //
+				.then(Mono.just(process));
+	}
+
+	Mono<Process> lookup(Integer id) {
+		return repository.findById(id);
+	}
+
+	Mono<Process> verify(Process process) {
+
+		Assert.state(process.getId() % 3 != 0, "We're sorry but we needed to drop that one");
+		return Mono.just(process);
+	}
+
+}