浅析mongoEngine的document对象

引言：

from mongoengine import *
connect('local')
class Test(Document):
    name=StringField(max_length=32)

t = Test(name='Tommy.Yu')

　　

方法

描述

DoesNotExist

None

MultipleObjectsReturned

None

cascade_save

Recursively saves any references / generic references on an objects

顺藤摸瓜式的保存所有被对象引用到的数据。就是保存EmbedDocument这种数据以及外键关联的数据。对象本身不做保存。如下：

>>> t2= Test(name='Joe')
>>> t2.cascade_save()
>>> t2.reload().to_json()

Traceback (most recent call last):
  File "<pyshell#121>", line 1, in <module>
    t2.reload().to_json()
  File "build\bdist.win-amd64\egg\mongoengine\document.py", line 457, in reload
    raise self.DoesNotExist("Document does not exist")
DoesNotExist: Document does not exist

clean

Hook for doing document level data cleaning before validation is run. Any ValidationError raised by this method will not be associated with a particular field; it will have a special-case association with the field defined by NON_FIELD_ERRORS.

compare_indexes

Compares the indexes defined in MongoEngine with the ones existing in the database. Returns any missing/extra indexes.

对比mongoengine和数据库的索引。返回缺失/多余的索引。和ensure_index(es)配合使用。

>>> t.ensure_index('name')
u'name_1'
>>> t.compare_indexes()
{'extra': [[(u'name', 1)]], 'missing': []}

delete

Delete the :class:`~mongoengine.Document` from the database. This will only take effect if the document has been previously saved.

:param write_concern: Extra keyword arguments are passed down which will be used as options for the resultant ``getLastError`` command.

For example, ``save(..., write_concern={w: 2, fsync: True}, ...)`` will wait until at least two servers have recorded the write and will force an fsync on the primary server.

从数据库中删除mongoengine.Document实例。 之前调用了save方法才起作用。

参数：write_concern: ...

例如， save(..., write_concern={w:2, fsync:True},...) 的实际调用的时机： 至少有两个服务器执行了写操作，将会迫使主服务器执行fsync(同步）。

>>> t2.delete()
>>> t2.to_json()
'{"_id": {"$oid": "54b71f7a4878c414e814d197"}, "name": "Tommy.yu"}'
>>> t3=t2.reload()

Traceback (most recent call last):
  File "<pyshell#93>", line 1, in <module>
    t3=t2.reload()
  File "build\bdist.win-amd64\egg\mongoengine\document.py", line 465, in reload
    raise self.DoesNotExist("Document does not exist")
DoesNotExist: Document does not exist

drop_collection

Drops the entire collection associated with this :class:`~mongoengine.Document` type from the database.

删除和mongoengine.Document子类关联的表(collection)。

>>> t.drop_collection()
>>> Test.objects.all()
[]

ensure_index

Ensure that the given indexes are in place. :param key_or_list: a single index key or a list of index keys (to construct a multi-field index); keys may be prefixed with a **+** or a **-** to determine the index ordering

在mongoenging中加入索引。影响的是整个类的，不是实例的。直到整个collection被删除(drop_collection被调用）都有效。

>>> t3=Test(name='John')
>>> t3.compare_indexes()
{'extra': [], 'missing': []}
>>> t3.ensure_index('name')
u'name_1'
>>> t3.compare_indexes()
{'extra': [[(u'name', 1)]], 'missing': []}

ensure_indexes

Checks the document meta data and ensures all the indexes exist.

Global defaults can be set in the meta - see :doc:`guide/defining-documents` .. note:: You can disable automatic index creation by setting `auto_create_index` to False in the documents meta data

检查document的meta信息，并且确保所有的索引都存在于（mongoengine/db?)

>>> class Test2(Document):
    name=StringField(max_length=100)
    url =StringField(max_length=100)
    meta={'indexes':['name','url']}

>>> t2=Test2(name='Tommy.Yu', url='http://www.cnblogs.com/Tommy-Yu')
>>> t2.ensure_indexes()
>>> t2.compare_indexes()
{'extra': [], 'missing': []}
>>> t2.list_indexes()
[[('name', 1)], [('url', 1)], [(u'_id', 1)]]
>>> t2.drop_collection()
>>> t2=Test2(name='Tommy.Yu', url='http://www.cnblogs.com/Tommy-Yu')
>>> t2.list_indexes()
[[('name', 1)], [('url', 1)], [(u'_id', 1)]]

实在是看不出来，看看数据库（经过测试，证实在save的时候已经创建了索引。索引对于性能的提升很夸张，看这里。）：

> db.test2.getIndexes()
[
        {
                "v" : 1,
                "key" : {
                        "_id" : 1
                },
                "name" : "_id_",
                "ns" : "local.test2"
        },
        {
                "v" : 1,
                "key" : {
                        "name" : 1
                },
                "name" : "name_1",
                "ns" : "local.test2",
                "background" : false,
                "dropDups" : false
        },
        {
                "v" : 1,
                "key" : {
                        "url" : 1
                },
                "name" : "url_1",
                "ns" : "local.test2",
                "background" : false,
                "dropDups" : false
        }
]

　　无法确定这个函数干嘛了。

from_json

将json数据转化为未保存的documeng对象。

>>> b= t.from_json('{"name":"joe"}')
>>> t.to_json()
'{"_id": {"$oid": "54b6353c4878c414e814d195"}, "name": "Tommy.Yu"}'
>>> b.to_json()
'{"name": "joe"}'

list_indexes

Lists all of the indexes that should be created for given collection. It includes all the indexes from super- and sub-classes.

列举出表(collection)的所有索引。包含父类和子类的！

>>> t.list_indexes()
[[(u'_id', 1)]]

my_metaclass

Metaclass for top-level documents (i.e. documents that have their own collection in the database.

register_delete_rule

This method registers the delete rules to apply when removing this object.

reload

从数据库重新加载所有属性

>>> a=t.reload()
>>> a is t
False
>>> a
<Test: Test object>
>>> a.to_json()
'{"_id": {"$oid": "54b6353c4878c414e814d195"}, "name": "Tommy.Yu"}'

save

>>>u.save()
<Test: Test object>

源码在这里。

保存 Document到数据库. 存在则修改，否则插入。

参数

force_insert – 不管数据是否存在，强制插入。默认为False validate – 是否验证输入数据，默认为True; clean – 是否调用clean方法，需要validate参数为True。默认为True。 write_concern – Extra keyword arguments are passed down to save() OR insert() which will be used as options for the resultant getLastError command. For example, save(..., write_concern={w: 2, fsync: True}, ...) will wait until at least two servers have recorded the write and will force an fsync on the primary server. cascade – 是否级联保存。可以在__meta__(class Meta)中设置这个属性，默认为None. cascade_kwargs – (可选) 传递给级联保存函数(cascade_save)的字典型参数。需要 cascade参数为True，默认为None. _refs – A list of processed references used in cascading saves。传递给级联保存函数的（已处理的？）引用列表。默认为None. save_condition – only perform save if matching record in db satisfies condition(s) (e.g., version number)。只有条件符合时，才保存数据。默认为None.

select_related

Handles dereferencing of :class:`~bson.dbref.DBRef` objects to a maximum depth in order to cut down the number queries to mongodb. .. versionadded:: 0.5

>>> t.select_related()
<Test: Test object>
>>> t.select_related(2)
<Test: Test object>

switch_collection

Temporarily switch the collection for a document instance. Only really useful for archiving off data and calling `save()`:: user = User.objects.get(id=user_id) user.switch_collection('old-users') user.save() If you need to read from another database see :class:`~mongoengine.context_managers.switch_db` :param collection_name: The database alias to use for saving the document

switch_db

Temporarily switch the database for a document instance. Only really useful for archiving off data and calling `save()`:: user = User.objects.get(id=user_id) user.switch_db('archive-db') user.save() If you need to read from another database see :class:`~mongoengine.context_managers.switch_db` :param db_alias: The database alias to use for saving the document

to_dbref

Returns an instance of :class:`~bson.dbref.DBRef` useful in `__raw__` queries.

返回bson.dbref.DBRef的实例。在'__raw__'查询时比较有用(pyMongo？)

>>>t.to_dbref()
DBRef('test', ObjectId('54b6353c4878c414e814d195'))

to_json

转换成json对象

>>>t.to_json()
'{"name": "Tommy.Yu"}'

to_mongo

Return as SON data ready for use with MongoDB.

>>> t.to_mongo()
SON([('_id', ObjectId('54b6353c4878c414e814d195')), ('name', u'Tommy.Yu')])

update

Performs an update on the :class:`~mongoengine.Document` A convenience wrapper to :meth:`~mongoengine.QuerySet.update`. Raises :class:`OperationError` if called on an object that has not yet been saved.

在mongoengine.Document类上进行更新操作。方法 mongoengine.QuerySet.update的简单包装。如果对象尚未调用save方法，会触发OperationError异常。

ps:源码。加入upsert参数是删除所有字段

>>> t.to_json()
'{"_id": {"$oid": "54b71e044878c414e814d196"}, "name": "Tommy.Yu"}'
>>> t.name='Tommy'
>>> t.update(upsert=True)
1
>>> t.to_json()
'{"_id": {"$oid": "54b71e044878c414e814d196"}, "name": "Tommy"}'
>>> t2=t.reload()
>>> t2.to_json()
'{"_id": {"$oid": "54b71e044878c414e814d196"}}'
>>> t.save()
<Test: Test object>
>>> t.to_json()
'{"_id": {"$oid": "54b71e044878c414e814d196"}}'

　　更新字段需要在栏位前面加入set__,如下：

>>> t.update(set__name='joe')
1
>>> t.reload()
<Test: Test object>
>>> t.to_json()
'{"_id": {"$oid": "54b6353c4878c414e814d195"}, "name": "joe"}'

　　

validate

Ensure that all fields' values are valid and that required fields are present.