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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.
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 (500 characters or less).
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 characters (which are not indexed), use a
Text
instance. For unencoded byte strings longer than 500 bytes (also not indexed), use a
Blob
instance. For non-textual unencoded byte strings up to 500 bytes (not characters) that should be indexed, use a
ByteString
instance.
Model property:
StringProperty
bool
A Boolean value (True
or False
).
Model property:
BooleanProperty
int
or long
An integer value, up to 64 bits.
Python int
values are converted to Python long
values prior to storage. A value stored as an int
will be returned as a long
.
If a long
larger than 64 bits is assigned, only the least significant 64 bits are stored.
Model property:
IntegerProperty
float
A floating-point number.
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:
import datetime import time class Pacific_tzinfo(datetime.tzinfo): """Implementation of the Pacific timezone.""" def utcoffset(self, dt): return datetime.timedelta(hours=-8) + self.dst(dt) def _FirstSunday(self, dt): """First Sunday on or after dt.""" return dt + datetime.timedelta(days=(6-dt.weekday())) def dst(self, dt): # 2 am on the second Sunday in March dst_start = self._FirstSunday(datetime.datetime(dt.year, 3, 8, 2)) # 1 am on the first Sunday in November dst_end = self._FirstSunday(datetime.datetime(dt.year, 11, 1, 1)) if dst_start <= dt.replace(tzinfo=None) < dst_end: return datetime.timedelta(hours=1) else: return datetime.timedelta(hours=0) def tzname(self, dt): if self.dst(dt) == datetime.timedelta(hours=0): return "PST" else: return "PDT" pacific_time = datetime.datetime.fromtimestamp(time.mktime(utc_time.timetuple()), 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.
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
blobstore.BlobKey
The key for a Blobstore value, generated by the Blobstore when the value is uploaded.
Model properties:
blobstore.BlobReferenceProperty
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
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", "rb").read())
In XML, blobs are base-64 encoded whether or not they contain binary data.
A short blob value (a "byte string") of 500 bytes or less. 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
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 characters 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")
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.
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.
A geographical point represented by floating-point latitude and longitude coordinates.
Model property:
GeoPtProperty
In XML, this is a
georss:point
element.
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.
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.
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.
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.
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.
All model property classes provided by google.appengine.ext.db
are subclasses of the base class
Property
,
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:
An uninterpreted collection of binary data.
Blob data is a byte string. For text data, which may involve encoding, use
TextProperty
.
Value type:
Blob
A Boolean value (True
or False
).
Value type:
bool
A short blob value (a "byte string") of 500 bytes or less.
ByteStringProperty
values are indexed, and can be used in filters and sort orders.
Like
StringProperty
,
except that the value is not encoded in any way. The bytes are stored literally.
If the ByteStringProperty
is required, the value cannot be an empty string.
Value type:
ByteString
A category or "tag," a descriptive word or phrase.
Value type:
Category
A date without a time of day; see
DateTimeProperty
for more information.
Value type:
datetime.date
;
converted internally to
datetime.datetime
A date and time.
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
An email address.
Neither the property class nor the value class perform validation of email addresses, they just store the value.
Value type:
Email
A floating-point number.
Value type:
float
A geographical point represented by floating-point latitude and longitude coordinates.
Value type:
GeoPt
An instant messaging handle.
Value type:
IM
An integer value, up to 64 bits.
Python int
values are converted to Python long
values prior to storage. A value stored as an int
will be returned as a long
.
If a long
larger than 64 bits is assigned, only the least significant 64 bits are stored.
A fully qualified URL.
Value type:
Link
A list of values of the type specified by item_type.
In a query, comparing a list property to a value performs the test against the members of the list: list_property
=
value
tests whether the value appears anywhere in the list, list_property
<
value
tests whether any of the list members 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
.
The value of a ListProperty
cannot be None
. It can, however, be an empty list. When None
is specified for the default argument (or when the default argument is not specified), the default value of the property is the 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 the Data Modeling page for more information on list properties and values.
Value type: a Python
list
of values of the specified type
A human-readable telephone number.
Value type:
PhoneNumber
A postal address.
Value type:
PostalAddress
A user-provided rating for a piece of content, as an integer between 0 and 100.
Value type:
Rating
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. The value of the property is a
Query
for all entities that reference the entity. If no collection_name is set, then modelname_set
(with the name of the referenced 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 reference property 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 author = db.get(author_key) stories_by_author = author.story_set.get()
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. Accessing an entity that does not exist raises a
ReferencePropertyResolveError
.
Deleting an entity does not delete entities referred to by a reference property.
Value type:
db.Key
A reference to another model instance of the same class (see
ReferenceProperty
).
Value type:
db.Key
A reference to the
BlobInfo
entity corresponding to a Blobstore value (see
ReferenceProperty
).
The value stored in the blob reference property is the Blobstore key. When the property is dereferenced, the corresponding BlobInfo
object is fetched and behaves as the value of the property. As with a reference property and model instance values, a blob reference property must be assigned a BlobInfo
object as its value.
Value type:
blobstore.BlobKey
Similar to a
list property
of Python str
or unicode
(basestring
) values.
A short string. Takes a Python str
or unicode
(basestring
) value of 500 characters or less.
StringProperty
values are indexed, and can be used in filters and sort orders.
If multiline is False
, 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.
If the string property is required, its value cannot be an empty string.
A long string.
Unlike
StringProperty
,
a TextProperty
value can be more than 500 characters 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
.
If the text property is required, its value cannot be an empty string.
Value type:
Text
A time of day without a date. Takes a Python standard library datetime.time
value; see
DateTimeProperty
for more information.
Value type:
datetime.time
;
converted internally to
datetime.datetime
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