Mongodb组和项目运营商 [英] Mongodb group and project operators
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问题描述
我正在尝试按"group_name"分组,并使用聚合框架通过php驱动程序选择"group_name"和"group_id"字段:
I'm trying to group by "group_name" and select fields "group_name" and "group_id" with php driver using aggregation framework:
Array
(
[$project] => Array
(
[group_name] => 1
[group_id] => 1
)
[$group] => Array
(
[_id] => $group_name
[total_sum] => Array
(
[$sum] => 1
)
)
)
我得到这个:[errmsg] => exception: A pipeline stage specification object must contain exactly one field.
但是,当我仅使用$project
或$group
运算符时,它就可以正常工作.
I'm getting this: [errmsg] => exception: A pipeline stage specification object must contain exactly one field.
However, when I'm using only $project
or $group
operator it works just fine.
推荐答案
问题是您将$ project和$ group分组在一起.
The issue is your grouping your $project and $group together.
您的数组应该更像
{
$project: {
group_name: 1,
group_id: 1
},
},
{
$group:{
_id:{
group_name:'$group_name',
},
total_sum:{$sum:1}
}
}
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