Question

我想知道如何使用MongoAlchemy关于嵌入式文档操作。但我没有找到任何关于这些的文件。谁能给我一些帮助？

以下是演示代码：

#!/usr/bin/python
# -*- coding: utf-8 -*-

from flask import Flask
from flaskext.mongoalchemy import MongoAlchemy

app = Flask(__name__)
app.config['DEBUG'] = True
app.config['MONGOALCHEMY_DATABASE'] = 'book'
db = MongoAlchemy(app)

class Comment(db.Document):
    user_id = db.StringField(db_field='uid')
    posted = db.StringField(db_field='posted')

class Book(db.Document):
    title = db.StringField()
    author = db.StringField()

    comments = db.ListField(db.DocumentField(Comment), db_field='Comments')

from mongoalchemy.session import Session
def test():
    with Session.connect('book') as s:
        s.clear_collection(Book)

    save()
    test_Book()

def save():
    title = "Hello World"
    author = 'me'

    comment_a = Comment(user_id='user_a', posted='post_a')
    comment_b = Comment(user_id='user_b', posted='post_b')
    comments = [comment_a, comment_b]

    book = Book(title=title, author=author, comments=comments)
    book.save()

def test_Book():
    book = Book.query.filter({'author':'me'}).first()
    comment = book.comments[0]
    comment.posted = str(book.comments[0].posted)+'_new'
    book.save()
    print 'change posted: Book.comments[0].posted:', book.comments[0].posted

    comment_c = Comment(user_id='user_c', posted='post_c')
    book.comments.append(comment_c)
    book.save()
    print 'append: Book.comments[2].posted:', book.comments[2].posted

    query = Book.query.filter({Book.comments:{'$elemMatch':{Comment.user_id:'user_c'}}}).limit(1).first()
    print 'query type:', type(query)

if __name__ == '__main__':
    test()

我想查询user_id为“user_c”的数据，然后返回一条评论，我该怎么做？以下这些方法是否被MongoAlchemy推荐？顺便说一句，这些方法将返回整个文档。

#query = Book.query.filter({Book.comments:{'uid':'user_c'}}).limit(1).first()
#query = Book.query_class(Comment).filter(Comment.user_id == 'user_c').limit(1).first()
#query = Book.query.filter({'comments':{'$elemMatch':{'uid':'user_c'}}}).limit(1).first()
#query = Book.query.filter({Book.comments:{'$elemMatch':{Comment.user_id:'user_c'}}}).limit(1).first()

如何通过查询将“user_c”更改为“user_c_new”？
如何删除user_id为“user_b”的一条评论？

Answer 1

Mongo不支持返回子文档。您可以使用$ elemMatch进行过滤，以便仅返回具有匹配属性的文档，但您必须自己获取注释。您可以通过仅返回注释字段进行略微优化，如下所示：

query = Book.query.filter({Book.comments:{'$elemMatch':{Comment.user_id:'user_c'}}})
query = query.fields(Book.comments.elem_match({Comment.user_id:'user_c'}))
result = query.limit(1).first()
print 'query result:', result.comments

请注意，直到0.14.3（我刚刚在几分钟前发布）出现了一个错误，这会导致results.comments无法正常工作。

另一个非常重要的注意事项是我在那里做的elem_match只返回第一个匹配元素。如果您想要所有匹配的元素，您必须自己过滤它们：

query = Book.query.filter({Book.comments:{'$elemMatch':{Comment.user_id:'user_c'}}})
result = query.limit(1).first()
print 'query result:', [c for c in result.comments if c.user_id == 'user_c']

MongoAlchemy查询嵌入式文档

1 个答案: