Datastore - NDB API(Python) : Property Type

NDB에서 사용하는 Property Types

Property type	Description
IntegerProperty	64-bit signed integer
FloatProperty	Double-precision floating-point number
BooleanProperty	Boolean
StringProperty	Unicode string; up to 500 characters, indexed
TextProperty	Unicode string; unlimited length, not indexed
BlobProperty	Uninterpreted byte string: if you set indexed=True, up to 500 characters, indexed; if indexed is False (the default), unlimited length, not indexed. Optional keyword argument: compressed.
DateTimeProperty	Date and time (see Date and Time Properties)
DateProperty	Date (see Date and Time Properties)
TimeProperty	Time (see Date and Time Properties)
GeoPtProperty	Geographical location. This is a ndb.GeoPt object. The object has attributes  lat and lon, both floats. You can construct one with two floats like  ndb.GeoPt(52.37, 4.88) or with a string  ndb.GeoPt("52.37, 4.88"). (This is actually the same class as db.GeoPt)
KeyProperty	Datastore key Optional keyword argument: kind=kind, to require that keys assigned to this property always have the indicated kind. May be a string or a Model subclass.
BlobKeyProperty	Blobstore key Corresponds to BlobReferenceProperty in the old db API, but the property value is a BlobKey instead of a BlobInfo; you can construct a BlobInfo from it using BlobInfo(blobkey)
UserProperty	User object.
StructuredProperty	Includes one kind of model inside another, by value (see Structured Properties)
LocalStructuredProperty	Like StructuredProperty, but on-disk representation is an opaque blob and is not indexed (see Structured Properties). Optional keyword argument: compressed.
JsonProperty	Value is a Python object (such as a list or a dict or a string) that is serializable using Python's json module; the Datastore stores the JSON serialization as a blob. Unindexed by default. Optional keyword argument: compressed.
PickleProperty	Value is a Python object (such as a list or a dict or a string) that is serializable using Python's pickle protocol; the Datastore stores the pickle serialization as a blob. Unindexed by default. Optional keyword argument: compressed.
GenericProperty	Generic value Used mostly by the Expando class, but also usable explicitly. Its type may be any of int, long, float, bool, str, unicode, datetime,Key, BlobKey, GeoPt, User, None.
ComputedProperty	Value computed from other properties by a user-defined function. (See Computed Properties.)

출처 : https://developers.google.com/appengine/docs/python/ndb/properties

Property가 가질수 있는 Options

Argument	Type	Default	Description
indexed	bool	UsuallyTrue	Include property in Datastore's indexes; if False, values cannot be queried but writes are faster. Not all property types support indexing; setting indexed to True fails for these. Unindexed properties cost fewer write ops than indexed properties.
repeated	bool	False	Property value is a Python list containing values of the underlying type (see Repeated Properties).
required	bool	False	Property must have a value specified. Cannot be combined with repeated=True  but can be combined with default=True.
default	Property's underlying type	None	Default value of property if none explicitly specified. Cannot be combined with repeated=True  but can be combined with required=True.
choices	List of values of underlying type	None	Optional list of allowable values.
validator	Function	None	Optional function to validate and possibly coerce the value. Will be called with arguments (prop, value) and should either return  the (possibly coerced) value or raise an exception.  Calling the function again on a coerced value should not  modify the value further.  (For example, returning value.strip() orvalue.lower() is fine,  but not value + '$'.)  May also return None, which means "no change".  See also Writing Property Subclasses
verbose_name	string	None	Optional HTML label to use in web form frameworks like jinja2.

출처 : https://developers.google.com/appengine/docs/python/ndb/properties

repeated (option)

복수의 데이터를 입력할때 사용된다. list 형태로 입력, 조회 된다.

class Article(ndb.Model):
    title = ndb.StringProperty()
    stars = ndb.IntegerProperty()
    tags = ndb.StringProperty(repeated=True)

art = Article(title='Python versus Ruby',
              stars=3,
              tags=['python', 'ruby'])
art.put()

뭐 이런식으로....

DateTimeProperty(DateProperty, TimeProperty)

DateTimeProperty는  date와 time 을 기록

DateProperty는 date만 기록

TimeProperty는 time만 기록

python 의 datetime 모듈로 매핑된다.

auto_now, auto_now_add 속성이 있는데

auto_now_add 속성을 True로 하면 데이터가 입력될 때만 현재시간 (UTC)을 입력하고

auto_now 속성을 True로 하면 입력, 수정 될 때마다 값이 자동으로 입력된다.

사용 예는

class Article(ndb.Model):

    title = ndb.StringProperty()
    stars = ndb.IntegerProperty()
    tags = ndb.StringProperty(repeated=True)
    date_time = ndb.DateTimeProperty(auto_now_add=True)

대충 위 처럼 사용하면 된다.

Structured Properties

string, int 이런 데이터 타입이 아닌 model 을 property로 사용 할 수 있다.

간단히 예를 보면

class Address(ndb.Model):
    type = ndb.StringProperty()
    street = ndb.StringProperty()
    city = ndb.StringProperty()
    
class Contact(ndb.Model):
    name = ndb.StringProperty()
    addresses = ndb.StructuredProperty(Address, repeated=True)

guido = Contact(name='Giudo',
                addresses=[Address(type='home', city='Amsterdam'),
                           Address(type='work', street='Spear St', city='SF')])
        
guido.put()

위와 같이 Contact 모델이 Address 모델을 property로 가질 수 있다.

Computed Properties

property를 지정하지 않고 다른 property를 이용해서 property를 만드는 타입

class SomeEntity(ndb.Model):
    name = ndb.StringProperty()
    name_lower = ndb.ComputedProperty(lambda self: self.name.lower())

x = SomeEntity(name='Nick')
#name = 'Nick'
#name_lower = 'nick'

위와 같이 name property를 할당하면 이걸 가지고 name_lower을 만들어 낸다.