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我尝试使用 MongoDB 存储库进行一些聚合。我使用了这些教程：https://www.mkyong.com/mongodb/spring-data-mongodb-aggregation-grouping-example/和https://docs.spring.io/spring-data/mongodb/docs/current/参考/html/#mongo.group。但是它们都不起作用，我不知道问题出在哪里。我的存储库看起来像：

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();

}

和 MongoTable 看起来像：

class MongoTable {

@Id
BigInteger id;
@Field
String skratka;
@Field
String zaciatok_studia;
@Field
int n;

...getter,setters, etc

问题是 MongoTemplate 给我错误Cannot make a static reference to the non-static method aggregate(Aggregation, String, Class<MongoTable>) from the type MongoTemplate，当我尝试将所有导入更改为静态导入时，它给了我：The static import org.springframework.data.mongodb.core.MongoTemplate must be a field or member type当我改变MongoTemplate.aggregate(agg, "studia", MongoTable.class);它mongoTemplate.aggregate(agg, "studia", MongoTable.class);时给我：The blank final field mongoTemplate may not have been initialized我不知道还有什么尝试。有什么帮助吗？

有配置：

@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();
    }

}

更新：所以我的项目中有新课程。

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();


}

和服务等级。

@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);

    }

}

问题是它仍然不起作用。它给了我一个nullpointer例外，System.out.println(repository2.mappedResult);看起来问题出在 AggregationRepository 中。聚合 agg 工作正常，但 mongoTemplate 为空。我想念什么？

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1 回答 1

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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，因此您得到了一个异常：

The blank final field mongoTemplate may not have been initialized
于 2018-04-26T20:19:31.213 回答