java - 如何获取集合中的最大字段值？

Question

我在 mongo 数据库中有一个名为 data 的集合。

spring 模型中的文档声明类似于:

@Document(collection = "data")
public class DataPoint {
    @Id
    private String id;

    private Long counter;
    ...
}

我想在数据点条目中找到最大计数器，或者至少找到具有最大值的 DataPoint。

我试着写:

@Repository
public interface DataPointRepository extends MongoRepository<DataPoint, String> {    
    DataPoint findFirstOrderByCounter();
}

在这种情况下，我在日志中看到:

org.springframework.data.repository.query.ParameterOutOfBoundsException: Invalid parameter index! You seem to have declare too little query method parameters!
    at org.springframework.data.repository.query.Parameters.getParameter(Parameters.java:207)
    at org.springframework.data.repository.query.Parameters.getBindableParameter(Parameters.java:277)
    at org.springframework.data.repository.query.ParametersParameterAccessor.getBindableValue(ParametersParameterAccessor.java:125)
    at org.springframework.data.repository.query.ParametersParameterAccessor$BindableParameterIterator.next(ParametersParameterAccessor.java:182)
    at org.springframework.data.mongodb.repository.query.ConvertingParameterAccessor$ConvertingIterator.next(ConvertingParameterAccessor.java:186)
    at org.springframework.data.mongodb.repository.query.MongoQueryCreator.from(MongoQueryCreator.java:247)
    at org.springframework.data.mongodb.repository.query.MongoQueryCreator.create(MongoQueryCreator.java:116)
    at org.springframework.data.mongodb.repository.query.MongoQueryCreator.create(MongoQueryCreator.java:60)
    at org.springframework.data.repository.query.parser.AbstractQueryCreator.createCriteria(AbstractQueryCreator.java:109)
    at org.springframework.data.repository.query.parser.AbstractQueryCreator.createQuery(AbstractQueryCreator.java:88)
    at org.springframework.data.repository.query.parser.AbstractQueryCreator.createQuery(AbstractQueryCreator.java:73)
    at org.springframework.data.mongodb.repository.query.PartTreeMongoQuery.createQuery(PartTreeMongoQuery.java:85)
    at org.springframework.data.mongodb.repository.query.AbstractMongoQuery.execute(AbstractMongoQuery.java:84)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:483)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:461)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:56)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)

我也试着关注 https://stackoverflow.com/a/35482658/2674303 的评论

然后写:

@Repository
public interface DataPointRepository extends MongoRepository<DataPoint, String> {
    @Query("select max(t.counter) from DataPoint t")
    DataPoint findFirstOrderByCounter();
}

在这种情况下，应用程序没有启动，我在日志中看到:

select max(t.counter) from DataPoint t
^
    at com.mongodb.util.JSONParser.parse(JSON.java:230)
    at com.mongodb.util.JSONParser.parse(JSON.java:155)
    at com.mongodb.util.JSON.parse(JSON.java:92)
    at com.mongodb.util.JSON.parse(JSON.java:73)
    at org.springframework.data.mongodb.repository.query.StringBasedMongoQuery$ParameterBindingParser.parseAndCollectParameterBindingsFromQueryIntoBindings(StringBasedMongoQuery.java:230)
    at org.springframework.data.mongodb.repository.query.StringBasedMongoQuery.<init>(StringBasedMongoQuery.java:93)
    at org.springframework.data.mongodb.repository.query.StringBasedMongoQuery.<init>(StringBasedMongoQuery.java:72)
    at org.springframework.data.mongodb.repository.support.MongoRepositoryFactory$MongoQueryLookupStrategy.resolveQuery(MongoRepositoryFactory.java:169)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.<init>(RepositoryFactorySupport.java:436)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport.getRepository(RepositoryFactorySupport.java:221)
    at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.initAndReturn(RepositoryFactoryBeanSupport.java:277)
    at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.afterPropertiesSet(RepositoryFactoryBeanSupport.java:263)
    at org.springframework.data.mongodb.repository.support.MongoRepositoryFactoryBean.afterPropertiesSet(MongoRepositoryFactoryBean.java:117)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1687)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1624)
    ... 42 common frames omitted

Answer 1

尝试以下方法名称:findFirstByOrderByCounterDesc

https://docs.spring.io/spring-data/mongodb/docs/2.0.1.RELEASE/reference/html/