问题描述

执行以下聚合管道:

public void getMostLikedItems () {
        UnwindOperation unwind = Aggregation.unwind("favoriteItems");
        GroupOperation group = Aggregation.group("favoriteItems").count().as("likes");
        SortOperation sort = Aggregation.sort(Sort.Direction.DESC, "likes");

        Aggregation aggregation = newAggregation(unwind, group, sort);
        DBObject result = mongoTemplate.aggregate(aggregation, "users", LikedItem.class).getRawResults();
}

抛出以下异常:

com.mongodb.MongoCommandException: Command failed with error 9: 'The 'cursor' option is required, except for aggregate with the explain argument' on server localhost:27017. The full response is { "ok" : 0.0, "errmsg" : "The 'cursor' option is required, except for aggregate with the explain argument", "code" : 9, "codeName" : "FailedToParse" }

我不明白这里的光标选项是什么意思.应该在哪里配置这个选项?

I don't understand what is meant by cursor option here. Where should this option be configured?

编辑这是一个示例用户文档

{
  "_id": "5a6df13552f42a34dcca9aa6",
  "username": "user1",
  "password": "$2a$10$p0OXq5PPa41j1e4iPcGZHuWjoKJ983sieS/ovFI.cVX5Whwj21WYi",
  "favoriteItems": [
    {
      "_id": "5a0c6b2dfd3eb67969316d6d",
      "name": "item1",
      "city": "Rabat"
    },
    {
      "_id": "5a0c680afd3eb67969316d0b",
      "name": "item2",
      "city": "Rabat"
    }
  ]
}

推荐答案

来自文档.

MongoDB 3.4 不赞成使用不带游标的聚合命令选项，除非管道包含解释选项.什么时候使用聚合命令内联返回聚合结果，使用默认批量大小光标指定光标选项:{} 或在游标选项 cursor: { batchSize:}.

MongoDB 3.4 deprecates the use of aggregate command without the cursor option, unless the pipeline includes the explain option. When returning aggregation results inline using the aggregate command, specify the cursor option using the default batch size cursor: {} or specify the batch size in the cursor option cursor: { batchSize: }.

您可以在 Spring Mongo 2.x 版本中使用 AggregationOptions 传递 batchSize

You can pass batchSize with AggregationOptions in Spring Mongo 2.x version

Aggregation aggregation = newAggregation(unwind, group).withOptions(newAggregationOptions().cursorBatchSize(100).build());

使用默认批量大小

Aggregation aggregation = newAggregation(unwind, group).withOptions(newAggregationOptions().cursor(new Document()).build());