spring-boot - spring data mongodb聚合管道的分页结果

Question

我在分页聚合管道的结果时遇到了一些麻烦。看完后In spring data mongodb how to achieve pagination for aggregation我想出了一个感觉像一个hacky的解决方案。我首先执行匹配查询，然后按我搜索的字段进行分组，并对结果进行计数，将值映射到私有(private)类:

private long getCount(String propertyName, String propertyValue) {
    MatchOperation matchOperation = match(
        Criteria.where(propertyName).is(propertyValue)
    );
    GroupOperation groupOperation = group(propertyName).count().as("count");
    Aggregation aggregation = newAggregation(matchOperation, groupOperation);
    return mongoTemplate.aggregate(aggregation, Athlete.class, NumberOfResults.class)
        .getMappedResults().get(0).getCount();
}

private class NumberOfResults {
    private int count;

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

这样，我就能够为返回的页面对象提供“总”值:

public Page<Athlete> findAllByName(String name, Pageable pageable) {
    long total = getCount("team.name", name);
    Aggregation aggregation = getAggregation("team.name", name, pageable);
    List<Athlete> aggregationResults = mongoTemplate.aggregate(
        aggregation, Athlete.class, Athlete.class
    ).getMappedResults();
    return new PageImpl<>(aggregationResults, pageable, total);
}

可以看到，得到结果总数的聚合与 并没有太大区别。实际聚合 我想执行:

MatchOperation matchOperation = match(Criteria.where(propertyName).is(propertyValue));
SkipOperation skipOperation = skip((long) (pageable.getPageNumber() * pageable.getPageSize()));
LimitOperation limitOperation = limit(pageable.getPageSize());
SortOperation sortOperation = sort(pageable.getSort());
return newAggregation(matchOperation, skipOperation, limitOperation, sortOperation);

这绝对有效，但是，正如我所说，它感觉很hacky。有没有一种方法可以获取 PageImpl 实例的计数，而无需运行两次查询？

Answer 1

您的问题帮助我解决了使用聚合进行分页的相同问题，因此我进行了一些挖掘并想出了解决您问题的方法。我知道这有点晚了，但有人可能会从这个答案中受益。我绝不是 Mongo 专家，所以如果我的做法不好或表现不佳，请不要犹豫，让我知道。

使用组，我们可以将根文档添加到集合中并进行计数。

group().addToSet(Aggregation.ROOT).as("documents")
       .count().as("count"))

这是我针对您面临的几乎完全相同的问题的解决方案。

private Page<Customer> searchWithFilter(final String filterString, final Pageable pageable, final Sort sort) {
    final CustomerAggregationResult aggregationResult = new CustomerAggregationExecutor()
        .withAggregations(match(new Criteria()
                .orOperator(
                    where("firstName").regex(filterString),
                    where("lastName").regex(filterString))),
            skip((long) (pageable.getPageNumber() * pageable.getPageSize())),
            limit(pageable.getPageSize()),
            sort(sort),
            group()
                .addToSet(Aggregation.ROOT).as("documents")
                .count().as("count"))
        .executeAndGetResult(operations);
    return new PageImpl<>(aggregationResult.getDocuments(), pageable, aggregationResult.getCount());
}

CustomerAggregationResult.java

@Data
public class CustomerAggregationResult {

  private int count;
  private List<Customer> documents;

  public static class PageableAggregationExecutor {

    private Aggregation aggregation;

    public CustomerAggregationExecutor withAggregations(final AggregationOperation... operations) {
      this.aggregation = newAggregation(operations);
      return this;
    }

    @SuppressWarnings("unchecked")
    public CustomerAggregationResult executeAndGetResult(final MongoOperations operations) {
        return operations.aggregate(aggregation, Customer.class, CustomerAggregationResult.class)
            .getUniqueMappedResult();
    }

  }
}

真的希望这会有所帮助。

编辑:我最初使用 List 创建了一个通用的 PageableAggregationResult ，但是当我传递没有 T 类型的 PageableAggregationResult.class 时，这会返回一个 IllegalArgumentException。如果我找到解决方案，我将编辑这个答案，因为我希望能够聚合多个集合最终。