Reactor，按值返回对象(Reactor, Boolean by value Returned object)

 我想根据型号名称创建一个新的集合。 如果有一个同名的集合，那么现有的集合正在返回。 如果不是，则新创建的集合返回。 我正在使用ReactiveCrudRepository。 我是新来的反应。 我在底层代码中得到这个错误。 我该怎么办？ 
 
public Mono<MongoCollection<Document>> constructDBCollection(String modelName) {
        return reactiveMongoOperations.collectionExists(modelName)
                .flatMap(exists -> exists ? reactiveMongoOperations.getCollection(modelName) : reactiveMongoOperations.createCollection(modelName, CollectionOptions.empty()
                .size(1024 * 1024)
                .capped()));
    }
 
 
 
 错误flatMap（java.util.function.Function>）的类型是错误的DBCollectionFactory.java /src/main/java/com/jagger/obls/factory/DBCollectionFactory.java:26 
 
 
 错误不兼容的类型：不能推断类型变量（R） 
 （参数不匹配; lambda表达式中的错误返回类型条件表达式中的错误类型 
 com.mongodb.reactivestreams.client.MongoCollection无法转换为reactor.core.publisher.Mono）DBCollectionFactory.java /src/main/java/com/jagger/obls/factory/DBCollectionFactory.java:26 
 

I want to create a new collection based on the model name. If there is a collection with the same name, then the existing one is returning. If not, the newly created collection returns. I'm using ReactiveCrudRepository. I'm new to reactive. I get this error in the underlying code. What should I do?
 
public Mono<MongoCollection<Document>> constructDBCollection(String modelName) {
        return reactiveMongoOperations.collectionExists(modelName)
                .flatMap(exists -> exists ? reactiveMongoOperations.getCollection(modelName) : reactiveMongoOperations.createCollection(modelName, CollectionOptions.empty()
                .size(1024 * 1024)
                .capped()));
    }
 
 
 
Error The type of flatMap(java.util.function.Function>) is erroneous DBCollectionFactory.java /src/main/java/com/jagger/obls/factory/DBCollectionFactory.java:26
 
 
Error incompatible types: cannot infer type-variable(s) R
 (argument mismatch; bad return type in lambda expression bad type in conditional expression
 com.mongodb.reactivestreams.client.MongoCollection cannot be converted to reactor.core.publisher.Mono) DBCollectionFactory.java /src/main/java/com/jagger/obls/factory/DBCollectionFactory.java:26
 

原文：https://stackoverflow.com/questions/48360011