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# Types and Property Classes

The App Engine datastore supports a fixed set of value types for properties on data entities. Property classes can define new types that are converted to and from the underlying value types, and the value types can be used directly with Expando dynamic properties and ListProperty aggregate property models.

The following table describes the Property classes whose values correspond directly with the underlying data types. Any of these value types can be used in an Expando dynamic property or ListProperty aggregate type.

Property class | Value type | Sort order
--- | --- | ---
StringProperty | str unicode | Unicode (`str` is treated as ASCII)
ByteStringProperty | ByteString | byte order
BooleanProperty | bool | `False` < `True`
IntegerProperty | int long | Numeric
FloatProperty | float | Numeric
DateTimeProperty DateProperty TimeProperty | datetime.datetime | Chronological
ListProperty StringListProperty | list of a supported type | If ascending, by least element; if descending, by greatest element
ReferenceProperty SelfReferenceProperty | db.Key | By path elements (kind, ID or name, kind, ID or name...)
UserProperty | users.User | By email address (Unicode)
BlobProperty | db.Blob | (not orderable)
TextProperty | db.Text | (not orderable)
CategoryProperty | db.Category | Unicode
LinkProperty | db.Link | Unicode
EmailProperty | db.Email | Unicode
GeoPtProperty | db.GeoPt | By latitude, then longitude
IMProperty | db.IM | Unicode
PhoneNumberProperty | db.PhoneNumber | Unicode
PostalAddressProperty | db.PostalAddress | Unicode
RatingProperty | db.Rating | Numeric

## Datastore Value Types

Datastore entity property values can be of one of the following types. See above for a list of corresponding Property classes to use with Model definitions.

Other than the Python standard types and users.User, all classes described in this section are provided by the `google.appengine.ext.db` module.

`str` or `unicode`

  A short string value, less than 500 bytes in length.

  A `str` value is assumed to be text encoded with the `ascii` codec, and is converted to a `unicode` value before being stored. The value is returned by the datastore as a `unicode` value. For short strings using other codecs, use a `unicode` value.

  Short strings are indexed by the datastore, and can be used in filters and sort orders. For text strings longer than 500 bytes (which are not indexed), use a Text instance. For unencoded byte strings longer than 500 bytes (also not indexed), use a Blob instance.

  Model property: StringProperty

`bool`

  A Boolean value, `True` or `False`.

  Model property: BooleanProperty

`int` or `long`

  An integer value.

  Python `int` values are converted to Python `long` values prior to storage. A value stored as an `int` will be returned as a `long`.

  Model property: IntegerProperty

`float`

  A floating point value.

  Model property: FloatProperty

`datetime.datetime`

  A date and time. See the datetime module documentation.

  If the `datetime` value has a `tzinfo` attribute, it will be converted to the UTC time zone for storage. Values come back from the datastore as UTC, with a `tzinfo` of `None`. An application that needs date and time values to be in a particular time zone must set `tzinfo` correctly when updating the value, and convert values to the timezone when accessing the value.

  Some libraries use the `TZ` environment variable to control the time zone applied to date-time values. App Engine sets this environment variable to `"UTC"`. Note that changing this variable in an application will not change the behavior of some datetime functions, because changes to environment variables are not visible outside of the Python code.

  If you only convert values to and from a particular time zone, you can implement a custom `datetime.tzinfo` to convert values from the datastore:

      class Pacific_tzinfo(datetime_module.tzinfo):
       """Implementation of the Pacific timezone."""
       def utcoffset(self, dt):
         return datetime_module.timedelta(hours=-8) + self.dst(dt)

       def _FirstSunday(self, dt):
         """First Sunday on or after dt."""
         return dt + datetime_module.timedelta(days=(6-dt.weekday()))

       def dst(self, dt):
         # 2 am on the second Sunday in March
         dst_start = self._FirstSunday(datetime_module.datetime(dt.year, 3, 8, 2))
         # 1 am on the first Sunday in November
         dst_end = self._FirstSunday(datetime_module.datetime(dt.year, 11, 1, 1))

         if dst_start <= dt.replace(tzinfo=None) < dst_end:
           return datetime_module.timedelta(hours=1)
         else:
           return datetime_module.timedelta(hours=0)

       def tzname(self, dt):
         if self.dst(dt) == datetime_module.timedelta(hours=0):
           return "PST"
         else:
           return "PDT"

      pacific_time = utc_time.astimezone(Pacific_tzinfo())

  See the datetime module documentation (including datetime.tzinfo). See also the third-party module pytz, though note that the pytz distribution has many files.

  The DateTimeProperty model property class includes features such as the ability to automatically use the date and time a model instance is stored. These are features of the model, and are not available on the raw datastore value (such as in an Expando dynamic property).

  Model properties: DateTimeProperty, DateProperty, TimeProperty

`list`

  A list of values, each of which is of one of the supported data types. See Entities and Models: Lists.

  When a `list` is used as the value of an Expando dynamic property, it cannot be an empty list. This is due to how list values are stored: When a list property has no items, it has no representation in the datastore. You can use a static property and the ListProperty class to represent an empty list value for a property.

  Model property: ListProperty

db.Key

  The key for another datastore entity.

      m = Employee(name="Susan", key_name="susan5")
      m.put()
      e = Employee(name="Bob", manager=m.key())
      e.put()

      m_key = db.Key.from_path("Employee", "susan5")
      e = Employee(name="Jennifer", manager=m_key)

  Model properties: ReferenceProperty, SelfReferenceProperty

users.User

  A user with a Google account.

  A User value in the datastore does not get updated if the user changes her email address. This may be remedied in a future release. Until then, you can use the User value's `user_id()` as the user's stable unique identifier.

  Model property: UserProperty

class Blob(arg=None)

  Binary data, as a byte string. This is a subclass of the built-in `str` type.

  Blob properties are not indexed, and cannot be used in filters or sort orders.

  Blob is for binary data, such as images. It takes a `str` value, but this value is stored as a byte string and is not encoded as text. Use a Text instance for large text data.

  Model property: BlobProperty

      class MyModel(db.Model):
        blob = db.BlobProperty()

      m = MyModel()
      m.blob = db.Blob(open("image.png").read())

  In XML, blobs are base-64 encoded whether or not they contain binary data.

class ByteString(arg)

  A short blob value (a "byte string"), less than 500 bytes in length. ByteString is a subclass of str, and takes an unencoded `str` value as an argument to its constructor.

  ByteStrings are indexed by the datastore, and can be used in filters and sort orders. For byte strings longer than 500 bytes (which are not indexed), use a Blob instance. For encoded text data, use str (short, indexed) or Text (long, not indexed).

  Model property: ByteStringProperty

class Text(arg=None, encoding=None)

  A long string. This is a subclass of the built-in `unicode` type.

  arg a `unicode` or `str` value. If arg is a `str`, then it is parsed with the encoding specified by encoding, or `ascii` if no encoding is specified. See the list of standard encodings for possible values for encoding.

  Unlike an entity property whose value is a simple `str` or `unicode`, a Text property can be more than 500 bytes long. However, Text properties are not indexed, and cannot be used in filters or sort orders.

  Model property: TextProperty

      class MyModel(db.Model):
        text = db.TextProperty()

      m = MyModel()
      m.text = db.Text(u"kittens")

      m.text = db.Text("kittens", encoding="latin-1")

class Category(tag)

  A category or "tag". This is a subclass of the built-in `unicode` type.

  Model property: CategoryProperty

      class MyModel(db.Model):
        category = db.CategoryProperty()

      m = MyModel()
      m.category = db.Category("kittens")

  In XML, this is an Atom `category` element. See the Atom specification.

class Email(email)

  An email address. This is a subclass of the built-in `unicode` type.

  Neither the property class nor the value class perform validation of email addresses, they just store the value.

  Model property: EmailProperty

      class MyModel(db.Model):
        email_address = db.EmailProperty()

      m = MyModel()
      m.email_address = db.Email("larry@example.com")

  In XML, this is a `gd:email` element. See the GData API reference.

class GeoPt(lat, lon=None)

  A geographical point represented by floating-point latitude and longitude coordinates.

  Model property: GeoPtProperty

  In XML, this is a `georss:point` element. See georss.org.

class IM(protocol, address=None)

  An instant messaging handle.

  protocol is the canonical URL of the instant messaging service. Some possible values:

  Protocol | Description
  --- | ---
  sip | SIP/SIMPLE
  xmpp | XMPP/Jabber
  http://aim.com/ | AIM
  http://icq.com/ | ICQ
  http://talk.google.com/ | Google Talk
  http://messenger.msn.com/ | MSN Messenger
  http://messenger.yahoo.com/ | Yahoo Messenger
  http://sametime.com/ | Lotus Sametime
  http://gadu-gadu.pl/ | Gadu-Gadu
  unknown | Unknown or unspecified

  address is the handle's address.

  Model property: IMProperty

      class MyModel(db.Model):
        im = db.IMProperty()

      m = MyModel()
      m.im = db.IM("http://example.com/", "Larry97")

  In XML, this is a `gd:im` element. See the GData API reference.

class Link(link)

  A fully qualified URL. This is a subclass of the built-in `unicode` type.

  Model property: LinkProperty

      class MyModel(db.Model):
        link = db.LinkProperty()

      m = MyModel()
      m.link = db.Link("http://www.google.com/")

  In XML, this is an Atom `link` element. See the Atom specification.

class PhoneNumber(phone)

  A human-readable telephone number. This is a subclass of the built-in `unicode` type.

  Model property: PhoneNumberProperty

      class MyModel(db.Model):
        phone = db.PhoneNumberProperty()

      m = MyModel()
      m.phone = db.PhoneNumber("1 (206) 555-1212")

  In XML, this is a `gd.phoneNumber` element. See the GData API reference.

class PostalAddress(address)

  A postal address. This is a subclass of the built-in `unicode` type.

  Model property: PostalAddressProperty

      class MyModel(db.Model):
        address = db.PostalAddressProperty()

      m = MyModel()
      m.address = db.PostalAddress("1600 Ampitheater Pkwy., Mountain View, CA")

  In XML, this is a `gd:postalAddress` element. See the GData API reference.

class Rating(rating)

  A user-provided rating for a piece of content, as an integer between 0 and 100. This is a subclass of the built-in `long` type. The class validates that the value is an integer between 0 and 100, and raises a BadValueError if the value is invalid.

  Model property: RatingProperty

      class MyModel(db.Model):
        rating = db.RatingProperty()

      m = MyModel()
      m.rating = db.Rating(97)

  In XML, this is a `gd:rating` element. See the GData API reference.

## Property Classes

All model property classes provided by `google.appengine.ext.db` are subclasses of the Property base class, and support all of the base constructor's arguments. See the base class documentation for information about those arguments.

The `google.appengine.ext.db` package provides the following model property classes:

class BlobProperty(...)

  A binary data property.

  Blob data is a byte string. For text data, which may involve encoding, use TextProperty.

  Value type: Blob

class BooleanProperty(...)

  A Boolean property.

  Value type: bool

class ByteStringProperty(verbose_name=None, ...)

  A short blob property (a "byte string"). Takes a ByteString value of 500 bytes or less.

  ByteStringProperty property values are indexed, and can be used in filters and sort orders.

  Like StringProperty, except the value is not encoded in any way. The bytes are stored literally.

  Value type: ByteString

class CategoryProperty(...)

  A category or "tag," a descriptive word or phrase.

  Value type: Category

class DateProperty(verbose_name=None, auto_now=False, auto_now_add=False, ...)

  A date property, without a time of day. See DateTimeProperty for more information.

  Value type: `datetime.date`. This is converted to a datetime.datetime internally.

class DateTimeProperty(verbose_name=None, auto_now=False, auto_now_add=False, ...)

  A date and time property.

  If auto_now is `True`, the property value is set to the current time whenever the model instance is stored in the datastore, overwriting the property's previous value. This is useful for tracking a "last modified" date and time for a model instance.

  If auto_now_add is `True`, the property value is set to the current time the first time the model instance is stored in the datastore, unless the property has already been assigned a value. This is useful for storing a "created" date and time for a model instance.

  Date-time values are stored as and returned using the UTC time zone. See datetime.datetime for a discussion of how to manage time zones.

  Value type: datetime.datetime

class EmailProperty(...)

  An email address.

  Neither the property class nor the value class perform validation of email addresses, they just store the value.

  Value type: Email

class FloatProperty(...)

  A floating point number property.

  Value type: float

class GeoPtProperty(...)

  A geographical point represented by floating-point latitude and longitude coordinates.

  Value type: GeoPt

class IMProperty(...)

  An instant messaging handle.

  Value type: IM

class IntegerProperty(...)

  An integer property.

  Python `int` values are converted to Python `long` values prior to storage. A value stored as an `int` will be returned as a `long`.

  Value type: int or long

class LinkProperty(...)

  A fully qualified URL.

  Value type: Link

class ListProperty(item_type, verbose_name=None, default=None, ...)

  A list of values of the type given as item_type.

  In a query, comparing a list property to a value performs the test against the list members: `list_property = value` tests if the value appears anywhere in the list, `list_property < value` tests if any of the members of the list are less than the given value, and so forth.

  A query cannot compare two list values. There is no way to test two lists for equality without testing each element for membership separately.

  item_type is the type of the items in the list, as a Python type or class. All items in the list value must be of the given type. item_type must be one of the datastore value types, and cannot be `list`. See Datastore Value Types, above.

  The value of a ListProperty static property cannot be `None`. It can, however, be an empty list.

  Tip: Because ListProperty aggregate types do not use the Property classes, Property class features such as automatic values and validation are not applied automatically to members of the list value. If you want to validate a member value using a Property class, you can instantiate the class and call its validate() method on the value.

  default is the default value for the list property. If `None`, the default is an empty list. A list property can define a custom validator to disallow the empty list.

  See Entities and Models for more information on ListProperty and list values.

  Value type: a Python list of zero or more values, where each value is of the configured type

class PhoneNumberProperty(...)

  A human-readable telephone number.

  Value type: PhoneNumber

class PostalAddressProperty(...)

  A postal address.

  Value type: PostalAddress

class RatingProperty()

  A user-provided rating for a piece of content, as an integer between 0 and 100.

  Value type: Rating

class ReferenceProperty(reference_class=None, verbose_name=None, collection_name=None, ...)

  A reference to another model instance. For example, a reference may indicate a many-to-one relationship between the model with the property and the model referenced by the property.

  reference_class is the model class of the model instance being referenced. If specified, only model instances of the class can be assigned to this property. If `None`, any model instance can be the value of this property.

  collection_name is the name of the property to give to the referenced model class whose value is a Query for all entities that reference the entity. If no collection_name is set, then `modelname_set` (with the name of the model in lowercase letters and "_set" added) is used.

  Note: collection_name must be set if there are multiple properties within the same model referencing the same model class. Otherwise, a `DuplicatePropertyError` will be raised when the default names are generated.

  ReferenceProperty automatically references and dereferences model instances as property values: A model instance can be assigned to a ReferenceProperty directly, and its key will be used. The ReferenceProperty value can be used as if it were a model instance, and the datastore entity will be fetched and the model instance created when it is first used in this way. Untouched reference properties do not query for unneeded data.

      class Author(db.Model):
        name = db.StringProperty()

      class Story(db.Model):
        author = db.ReferenceProperty(Author)

      story = db.get(story_key)
      author_name = story.author.name

  As with a Key value, it is possible for a reference property value to refer to a data entity that does not exist. If a referenced entity is deleted from the datastore, references to the entity are not updated. An application can explicitly db.get() the value of a ReferenceProperty (which is a Key) to test whether the referenced entity exists.

  Deleting an entity does not delete entities referred to by a ReferenceProperty.

  See also this introduction to reference properties.

  Value type: db.Key (see above)

class SelfReferenceProperty(verbose_name=None, collection_name=None, ...)

  A reference to another model instance of the same class. See ReferenceProperty.

  Value type: db.Key (see above)

class StringListProperty(verbose_name=None, default=None, ...)

  Similar to a ListProperty of Python `str` or `unicode` (`basestring`) values. See ListProperty.

  Value type: a Python `list` of str or unicode values

class StringProperty(verbose_name=None, multiline=False, ...)

  A short string property. Takes a Python `str` or `unicode` (`basestring`) value of 500 bytes or less.

  StringProperty property values are indexed, and can be used in filters and sort orders.

  If multiline is `False`, then the value cannot include linefeed characters. The `djangoforms` library uses this to enforce a difference between text fields and textarea fields in the data model, and others can use it for a similar purpose.

  Value type: str or unicode

class TextProperty()

  A long string.

  Unlike StringProperty, a TextProperty value can be more than 500 bytes long. However, TextProperty values are not indexed, and cannot be used in filters or sort orders.

  TextProperty values store text with a text encoding. For binary data, use BlobProperty.

  Value type: Text

class TimeProperty(verbose_name=None, auto_now=False, auto_now_add=False, ...)

  A time property, without a date. Takes a Python standard library datetime.time value. See DateTimeProperty for more information.

  Value type: `datetime.time`. This is converted to a datetime.datetime internally.

class UserProperty(verbose_name=None, auto_current_user=False, auto_current_user_add=False, ...)

  A user with a Google account.

  If auto_current_user is `True`, the property value is set to the currently signed-in user whenever the model instance is stored in the datastore, overwriting the property's previous value. This is useful for tracking which user modifies a model instance.

  If auto_current_user_add is `True`, the property value is set to the currently signed-in user the first time the model instance is stored in the datastore, unless the property has already been assigned a value. This is useful for tracking which user creates a model instance, which may not be the same user that modifies it later.

  UserProperty does not accept a default value. Default values are set when the model class is first imported, and with import caching may not be the currently signed-in user.

  Value type: users.User (see above)