包括所有现有字段并将新字段添加到文档 [英] Include all existing fields and add new fields to document
问题描述
我想定义一个 $project 聚合阶段,我可以指示它添加一个新字段并包含所有现有字段,而无需列出所有现有字段.
I would like to define a $project aggregation stage where I can instruct it to add a new field and include all existing fields, without having to list all the existing fields.
我的文档看起来像这样,有很多字段:
My document looks like this, with many fields:
{
obj: {
obj_field1: "hi",
obj_field2: "hi2"
},
field1: "a",
field2: "b",
...
field26: "z"
}
我想做这样的聚合操作:
I want to make an aggregation operation like this:
[
{
$project: {
custom_field: "$obj.obj_field1",
//the next part is that I don't want to do
field1: 1,
field2: 1,
...
field26: 1
}
},
... //group, match, and whatever...
]
在这种情况下,是否可以使用诸如包含所有字段"之类的关键字,或者使用其他方法来避免必须单独列出每个字段?
Is there something like an "include all fields" keyword that I can use in this case, or some other way to avoid having to list every field separately?
推荐答案
在 4.2+ 中,您可以使用 $set
聚合管道操作符,它只不过是 $addFields
在 3.4 中添加
In 4.2+, you can use the $set
aggregation pipeline operator which is nothing other than an alias to $addFields
added in 3.4
$addFields
阶段相当于一个 $project
阶段,明确指定输入文档中的所有现有字段并添加新字段.
The
$addFields
stage is equivalent to a$project
stage that explicitly specifies all existing fields in the input documents and adds the new fields.
db.collection.aggregate([
{ "$addFields": { "custom_field": "$obj.obj_field1" } }
])
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