淺析mongoEngine的document對象

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 順藤摸瓜式的保存全部被對象引用到的數據。就是保存EmbedDocument這種數據以及外鍵關聯的數據。對象自己不作保存。以下： >>> 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. 對比mongoengine和數據庫的索引。返回缺失/多餘的索引。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. 從數據庫中刪除mongoengine.Document實例。 以前調用了save方法才起做用。 參數：write_concern: ... 例如， save(..., write_concern={w:2, fsync:True},...) 的實際調用的時機： 至少有兩個服務器執行了寫操做，將會迫使主服務器執行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. 刪除和mongoengine.Document子類關聯的表(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。影響的是整個類的，不是實例的。直到整個collection被刪除(drop_collection被調用）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 檢查document的meta信息，而且確保全部的索引都存在於（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)]]  實在是看不出來，看看數據庫（通過測試，證明在save的時候已經建立了索引。索引對於性能的提高很誇張，看這裏。）： > 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 } ] 　　沒法肯定這個函數幹嗎了。
from_json	將json數據轉化爲未保存的documeng對象。 >>> 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. 列舉出表(collection)的全部索引。包含父類和子類的！ >>> 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	從數據庫從新加載全部屬性 >>> 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> 源碼在這裏。 保存 Document到數據庫. 存在則修改，不然插入。 參數 force_insert – 無論數據是否存在，強制插入。默認爲False validate – 是否驗證輸入數據，默認爲True;  clean – 是否調用clean方法，須要validate參數爲True。默認爲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 – 是否級聯保存。能夠在__meta__(class Meta)中設置這個屬性，默認爲None. cascade_kwargs – (可選) 傳遞給級聯保存函數(cascade_save)的字典型參數。須要 cascade參數爲True，默認爲None. _refs – A list of processed references used in cascading saves。傳遞給級聯保存函數的（已處理的？）引用列表。默認爲None. save_condition – only perform save if matching record in db satisfies condition(s) (e.g., version number)。只有條件符合時，才保存數據。默認爲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的實例。在'__raw__'查詢時比較有用(pyMongo？) >>>t.to_dbref() DBRef('test', ObjectId('54b6353c4878c414e814d195'))
to_json	轉換成json對象 >>>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類上進行更新操做。方法 mongoengine.QuerySet.update的簡單包裝。若是對象還沒有調用save方法，會觸發OperationError異常。 ps:源碼。加入upsert參數是刪除全部字段 >>> 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": {"$oid": "54b71e044878c414e814d196"}}' 　　更新字段須要在欄位前面加入set__,以下： >>> t.update(set__name='joe') 1 >>> t.reload() <Test: Test object> >>> t.to_json() '{"_id": {"$oid": "54b6353c4878c414e814d195"}, "name": "joe"}'
validate	Ensure that all fields' values are valid and that required fields are present.