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MongoDB 在 Spring Data 中的应用通常涉及多种查询方法，本文将从多个角度探讨如何高效地与 MongoDB 数据库交互。

一、基于 MongoRepository 的实现

最直接的方法是继承 MongoRepository 接口，利用其强大的查询功能。具体实现如下：

public interface StudentRepository extends MongoRepository<, Student> {}

在实现中，主要采用 ExampleMatcher 作为匹配器，支持模糊查询和大小写忽略。以下是典型的代码实现：

public Page
   
     getListWithExample(StudentReqVO studentReqVO) {    Sort sort = Sort.by(Sort.Direction.DESC, "createTime");    Pageable pageable = PageRequest.of(studentReqVO.getPageNum(), studentReqVO.getPageSize(), sort);    Student student = new Student();    BeanUtils.copyProperties(studentReqVO, student);        ExampleMatcher matcher = ExampleMatcher.matching()        .withStringMatcher(ExampleMatcher.StringMatcher.CONTAINING)        .withIgnoreCase(true)        .withMatcher("name", ExampleMatcher.GenericPropertyMatchers.contains())        .withIgnorePaths("pageNum", "pageSize");        Example
    
      example = Example.of(student, matcher);    Page
     
       students = studentRepository.findAll(example, pageable);    return students;}
     
    
   

优点：支持模糊查询和复杂条件组合。

缺点：不支持范围查询和过滤条件分组。

二、基于 MongoDB Template 的实现

MongoTemplate 提供了更加灵活的查询方式，以下是两种典型实现。

实现一：使用 Criteria 封装查询条件

public Page
   
     getListWithCriteria(StudentReqVO studentReqVO) {    Sort sort = Sort.by(Sort.Direction.DESC, "createTime");    Pageable pageable = PageRequest.of(studentReqVO.getPageNum(), studentReqVO.getPageSize(), sort);        Query query = new Query();        if (!StringUtils.isEmpty(studentReqVO.getName())) {        Pattern pattern = Pattern.compile("^.*" + studentReqVO.getName() + ".*$", Pattern.CASE_INSENSITIVE);        query.addCriteria(Criteria.where("name").regex(pattern));    }        if (studentReqVO.getSex() != null) {        query.addCriteria(Criteria.where("sex").is(studentReqVO.getSex()));    }        if (studentReqVO.getCreateTime() != null) {        query.addCriteria(Criteria.where("createTime").lte(studentReqVO.getCreateTime()));    }        long total = mongoTemplate.count(query, Student.class);    List
    
      studentList = mongoTemplate.find(query.with(pageable), Student.class);        PageImpl studentPage = new PageImpl(studentList, pageable, total);    return studentPage;}
    
   

实现二：结合 Example 和 Criteria

public Page
   
     getListWithExampleAndCriteria(StudentReqVO studentReqVO) {    Sort sort = Sort.by(Sort.Direction.DESC, "createTime");    Pageable pageable = PageRequest.of(studentReqVO.getPageNum(), studentReqVO.getPageSize(), sort);        Student student = new Student();    BeanUtils.copyProperties(studentReqVO, student);        ExampleMatcher matcher = ExampleMatcher.matching()        .withStringMatcher(ExampleMatcher.StringMatcher.CONTAINING)        .withIgnoreCase(true)        .withMatcher("name", ExampleMatcher.GenericPropertyMatchers.contains())        .withIgnorePaths("pageNum", "pageSize");        Example
    
      example = Example.of(student, matcher);    Query query = new Query(Criteria.byExample(example));        if (studentReqVO.getCreateTime() != null) {        query.addCriteria(Criteria.where("createTime").lte(studentReqVO.getCreateTime()));    }        long total = mongoTemplate.count(query, Student.class);    List
     
       studentList = mongoTemplate.find(query.with(pageable), Student.class);        PageImpl studentPage = new PageImpl(studentList, pageable, total);    return studentPage;}
     
    
   

优点：支持复杂查询条件和模糊搜索。

缺点：不支持返回固定字段。

三、基于 BasicQuery 的实现

BasicQuery 是 Query 的子类，支持返回固定字段，查询速度较快，适合大数据量的场景。

public Page
   
     getListWithBasicQuery(StudentReqVO studentReqVO) {    Sort sort = Sort.by(Sort.Direction.DESC, "createTime");    Pageable pageable = PageRequest.of(studentReqVO.getPageNum(), studentReqVO.getPageSize(), sort);        QueryBuilder queryBuilder = new QueryBuilder();        if (!StringUtils.isEmpty(studentReqVO.getName())) {        Pattern pattern = Pattern.compile("^.*" + studentReqVO.getName() + ".*$", Pattern.CASE_INSENSITIVE);        queryBuilder.and("name").regex(pattern);    }        if (studentReqVO.getSex() != null) {        queryBuilder.and("sex").is(studentReqVO.getSex());    }        if (studentReqVO.getCreateTime() != null) {        queryBuilder.and("createTime").lessThanEquals(studentReqVO.getCreateTime());    }        BasicDBObject fieldsObject = new BasicDBObject();    fieldsObject.append("id", 1);    fieldsObject.append("name", 1);        Query query = new BasicQuery(queryBuilder.get().toString(), fieldsObject.toJson());        long total = mongoTemplate.count(query, Student.class);    List
    
      studentList = mongoTemplate.find(query.with(pageable), Student.class);        PageImpl studentPage = new PageImpl(studentList, pageable, total);    return studentPage;}
    
   

优点：支持固定字段返回和快速查询。

缺点：不支持复杂的聚合操作。

四、基于 Aggregation 的实现

Aggregation 提供了更强大的查询功能，支持分组、聚合等操作。

public Page
   
     getListWithAggregation(StudentReqVO studentReqVO) {    Sort sort = Sort.by(Sort.Direction.DESC, "createTime");    Pageable pageable = PageRequest.of(studentReqVO.getPageNum(), studentReqVO.getPageSize(), sort);        Integer pageNum = studentReqVO.getPageNum();    Integer pageSize = studentReqVO.getPageSize();        List
    
      operations = new ArrayList<>();        if (!StringUtils.isEmpty(studentReqVO.getName())) {        Pattern pattern = Pattern.compile("^.*" + studentReqVO.getName() + ".*$", Pattern.CASE_INSENSITIVE);        Criteria criteria = Criteria.where("name").regex(pattern);        operations.add(Aggregation.match(criteria));    }        if (null != studentReqVO.getSex()) {        operations.add(Aggregation.match(Criteria.where("sex").is(studentReqVO.getSex())));    }        if (operations.size() > 0) {        Aggregation aggregationCount = Aggregation.newAggregation(operations);        AggregationResults
     
       resultsCount = mongoTemplate.aggregate(aggregationCount, "student", Student.class);        long totalCount = resultsCount.getMappedResults().size();    } else {        List
      
        list = mongoTemplate.findAll(Student.class);        totalCount = list.size();    }        operations.add(Aggregation.skip((long) pageNum * pageSize));    operations.add(Aggregation.limit(pageSize));    operations.add(Aggregation.sort(Sort.Direction.DESC, "createTime"));        Aggregation aggregation = Aggregation.newAggregation(operations);    AggregationResults
       
         results = mongoTemplate.aggregate(aggregation, "student", Student.class);        PageImpl studentPage = new PageImpl(results.getMappedResults(), pageable, totalCount);    return studentPage;}
       
      
     
    
   

优点：支持分组、聚合和复杂查询。

缺点：查询速度较慢，建议用于数据量较小的场景。

总结

以上方法各有优劣，选择时需要根据具体需求决定。基于 Example Matcher 的方法适合支持模糊查询的场景，而 BasicQuery 和 Aggregation 方法则适合需要固定字段返回或复杂聚合的场景。