如何在mongoengine中只包含选定的嵌入式文档？

Question

我正在根据特定的EmbeddedDocument获取文档，但我不想在检索时获取所有的EmbeddedDocuments，只有匹配的EmbeddedDocument和主Document。

这是我的密码：

学校嵌入式文档

class School(EmbeddedDocument):
    name = StringField(max_length=120)

用户文档

class User(Document):
    first_name = StringField(max_length=60, required=True)
    last_name = StringField(max_length=60)
    schools = EmbeddedDocumentListField(School)

供餐文件：

user = User.objects.create(first_name="Rohit", last_name="Khatri")
user.schools = [
    School(name="Auden High School")),
    School(name="Baldwin Boys High School"),
    School(name="Baldwin Girls High School"),
    School(name="Aukamm Elementary School"),
    School(name="Mason-Rice Elementary")
]
user.save()

user = User.objects.create(first_name="ABC", last_name="DEF")
user.schools = [
    School(name="Little Harbor Elementary School")),
    School(name="Aukamm Elementary School"),
    School(name="Mason-Rice Elementary")
]
user.save()

我使用这段代码，检索在schools字段中有特定学校的schools：

users = User.objects(school__match={"name": "Aukamm Elementary School"})

我只想得到选定的学校，这是Aukamm Elementary School在学校领域。

接收

[
    {
        "first_name": "Rohit",
        "last_name": "Khatri",
        "schools": [
            {
                "name": "Auden High School"
            },
            {
                "name": "Baldwin Boys High School"
            },
            {
                "name": "Baldwin Girls High School"
            },
            {
                "name": "Aukamm Elementary School"
            },
            {
                "name": "Mason-Rice Elementary"
            }
        ]
    },
    {
        "first_name": "ABC",
        "last_name": "DEF",
        "schools": [
            {
                "name": "Little Harbor Elementary School"
            },
            {
                "name": "Aukamm Elementary School"
            },
            {
                "name": "Mason-Rice Elementary"
            }
        ]
    }
]

所需输出

[
    {
        "first_name": "Rohit",
        "last_name": "Khatri",
        "schools": [
            {
                "name": "Aukamm Elementary School"
            }
        ]
    },
    {
        "first_name": "ABC",
        "last_name": "DEF",
        "schools": [
            {
                "name": "Aukamm Elementary School"
            }
        ]
    }
]

谢谢

Answer 1

您可以在$filter函数中使用aggregate运算符

users = User.objects(school__match={ "name": "Aukamm Elementary School" }).aggregate(
    { "$project": {
        "first_name": 1,
        "last_name": 1,
        "schools": {
             "$filter": {
                  "input": "$schools",
                  "as": "school",
                  "cond": { "$eq": [ "$$school.name", "Aukamm Elementary School" ] }
             }
        }
    } }
)