红帽全球峰会228.5.5. 其他操作
228.5.5.1. aggregate
使用正文中包含的给定管道执行聚合。聚合可能比较长且重度的操作。谨慎使用。
// route: from("direct:aggregate").to("mongodb3:myDb?database=science&collection=notableScientists&operation=aggregate");
List<Bson> aggregate = Arrays.asList(match(or(eq("scientist", "Darwin"), eq("scientist",
group("$scientist", sum("count", 1)));
from("direct:aggregate")
.setBody().constant(aggregate)
.to("mongodb3:myDb?database=science&collection=notableScientists&operation=aggregate")
.to("mock:resultAggregate");支持以下 IN 消息标头：
| 标头密钥 | 快速持续 | 描述（从 MongoDB API doc中提取） | 预期类型 |
|---|---|---|---|
|
|
| 设置每个批处理要返回的文档数量。 | int/Integer |
|
|
| 启用聚合管道阶段，将数据写入临时文件。 | boolean/Boolean |
通过 outputType=MongoIterable 支持有效的检索。
您还可以通过包含 outputType=DBCursor (Camel 2.21+)作为 endpoint 选项，从服务器返回至您的路由的文档可能比设置上述标头更简单。这了来自 Mongo 驱动程序的 DBCursor，就像您在 Mongo shell 中执行 aggregate （）一样，允许您的路由迭代结果。默认情况下，如果不使用此选项，此组件会将驱动程序的光标中的文档加载到列表，并将此数据返回到您的路由 - 这可能导致大量内存对象。请记住，使用 DBCursor 并不要求提供匹配的文档数量 - 请参阅 MongoDB 文档网站了解详细信息。
带有选项 outputType=MongoIterable 和 batch 大小示例：
// route: from("direct:aggregate").to("mongodb3:myDb?database=science&collection=notableScientists&operation=aggregate&outputType=MongoIterable");
List<Bson> aggregate = Arrays.asList(match(or(eq("scientist", "Darwin"), eq("scientist",
group("$scientist", sum("count", 1)));
from("direct:aggregate")
.setHeader(MongoDbConstants.BATCH_SIZE).constant(10)
.setBody().constant(aggregate)
.to("mongodb3:myDb?database=science&collection=notableScientists&operation=aggregate&outputType=MongoIterable")
.to("mock:resultAggregate");
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