Question

我尝试与MongoDB存储库进行一些聚合。我使用了以下教程：https://www.mkyong.com/mongodb/spring-data-mongodb-aggregation-grouping-example/和https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#mongo.group。但是他们都没有工作，我不知道问题出在哪里。我的存储库看起来像：

<metadata xmlns="http://musicbrainz.org/ns/mmd-2.0#" xmlns:ext="http://musicbrainz.org/ns/ext#-2.0" created="2018-04-25T14:25:36.224Z">
  <recording-list count="526823" offset="0">
    ...
  </recording-list>
</metadata>

和MongoTable看起来像：

import java.math.BigInteger;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Sort.Direction;

import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;

import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.aggregation.AggregationResults;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface StudentRepository extends CrudRepository<MongoStudent, String> {

    @Autowired
    MongoTemplate mongoTemplate;

    Aggregation agg = newAggregation(project("studium"), unwind("studium"), group("studium").count().as("n"),
            project("n").and("studium").previousOperation(), sort(Sort.Direction.DESC, "total"));

    AggregationResults<MongoTable> results = MongoTemplate.aggregate(agg, "studium", MongoTable.class);
    List<MongoTable> mappedResult = results.getMappedResults();

}

问题是MongoTemplate给了我错误class MongoTable { @Id BigInteger id; @Field String skratka; @Field String zaciatok_studia; @Field int n; ...getter,setters, etc，当我尝试将所有导入更改为静态导入时，它会给我：Cannot make a static reference to the non-static method aggregate(Aggregation, String, Class<MongoTable>) from the type MongoTemplate当我将The static import org.springframework.data.mongodb.core.MongoTemplate must be a field or member type更改为MongoTemplate.aggregate(agg, "studia", MongoTable.class);时给我：mongoTemplate.aggregate(agg, "studia", MongoTable.class);我不知道还有什么尝试。有什么帮助吗？

有配置：

The blank final field mongoTemplate may not have been initialized

更新：所以我的项目中有新课程。

@EnableMongoRepositories
@Configuration
@ComponentScan(basePackages = "com.nosql")
public class MongoConfig extends AbstractMongoConfiguration{

    static MongoClient mongo = null;

      @Bean("applicationTemplate")
      @Qualifier("applicationTemplate")
      public MongoTemplate mongoTemplate(
          final MappingMongoConverter mappingMongoConverter, final MongoClient mongoClient) {
        final String databaseName = mongo.getDatabase("mynosqlproject").getName();

        final MongoDbFactory dbFactory = new SimpleMongoDbFactory(mongoClient, databaseName);
        return new MongoTemplate(dbFactory, mappingMongoConverter);
      }

    @Override
    public MongoClient mongoClient() {
        // Creating a Mongo client
                MongoClientURI uri = new MongoClientURI(
                        "mongodb://xxx:xxx/mynosqlproject");
                 mongo = new MongoClient(uri);
                 return mongo;
    }

    @Override
    protected String getDatabaseName() {
                return mongo.getDatabase("mynosqlproject").getName();
    }

}

服务类。

public class AggregationRepository {

    Aggregation agg = newAggregation( unwind("studium"), group("course","start").count().as("n"), sort(Sort.Direction.DESC,"n"));

    @Autowired
    MongoTemplate mongoTemplate;

    AggregationResults<MongoTable> results = mongoTemplate.aggregate(agg, "studium",MongoTable.class);
    List<MongoTable> mappedResult = results.getMappedResults();


}

问题是它仍然无效。它在@Service public class StudentService { @Autowired private StudentRepository repository; private AggregationRepository repository2; public void saveData() { .... } public void findStudentsFromYear() { .... } public void findStudentsDromCourse() { ...... } public void AggreagationTable() { List<MongoTable> mappedResult = repository2.mappedResult; mappedResult.forEach(System.out::println); } }给我nullpointer异常看起来问题在于AggregationRepository。聚合agg工作正常，但mongoTemplate为null。我错过了什么？

Answer 1

将接口StudentRepository更改为简单的java类并删除扩展CrudRepository并添加方法返回：

List<MongoTable>

您尝试将bean注入接口，因此您得到了一个例外：

The blank final field mongoTemplate may not have been initialized

MongoDB存储库 - 聚合 - Mongo模板不起作用

1 个答案: