Mongo Grouping 并不在 DB 级别发生, 也没有使用下列代码的 Mongo 聚合框架 。 知道为什么吗? 我必须创建命令文档和 RunCommand, 然后它只使用聚合框架 。
public IEnumerable<IGrouping<TKey, T>> GetItemsByQuery<TKey>(IMongoQuery query, FieldsBuilder fieldsBuilder, Func<T, TKey> groupbyKey)
{
var mongoCursor = collection.FindAs<T>(query);
mongoCursor.SetFields(fieldsBuilder);
return mongoCursor.GroupBy(groupbyKey);
}
(1) 聚合框架只是支持MongoDB 2. 1 版本或更高版本的不稳定释放。 它将在服务器2.2 中正式支持。 所以, 除非您正在运行服务器 2. 1 或以上, 否则您将无法获得此功能服务器侧面 。
(2) 驱动程序尚未支持聚合框架。 您可以手动构建聚合, 并使用 db.RunCommand 执行它 。
3) 您正在从一个 MongoCursor 调用无数的扩展方法 。 MongoCursor 确实知道您要它做什么, 因此, 组合会发生在客户端 。 收藏上有一个方法叫做 Group, 但是您需要写一些 javascript 来执行它 。
总而言之,我们还没有一个伟大的汇总故事。在服务器2.2中,这将会改变,但还没有改变。
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