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A datastore query.
Inherits From: expected_type
google.appengine.api.datastore.Query(
kind=None,
filters={},
_app=None,
keys_only=False,
compile=True,
cursor=None,
namespace=None,
end_cursor=None,
projection=None,
distinct=None,
_namespace=None,
_read_time_us=None
)
(Instead of this, consider using appengine.ext.gql.Query! It provides a query language interface on top of the same functionality.)
Queries are used to retrieve entities that match certain criteria, including app id, kind, and property filters. Results may also be sorted by properties.
App id and kind are required. Only entities from the given app, of the given
type, are returned. If an ancestor is set, with Ancestor()
, only entities
with that ancestor are returned.
Property filters are used to provide criteria based on individual property values. A filter compares a specific property in each entity to a given value or list of possible values.
An entity is returned if its property values match all of the query's
filters. In other words, filters are combined with AND
, not OR
. If an
entity does not have a value for a property used in a filter, it is not
returned.
Property filters map filter strings of the form '
> query = Query('Person')
> query['name ='] = 'Ryan'
> query['age >='] = 21
This query returns all Person entities where the name property is 'Ryan' and the age property is at least 21.
Another way to build this query is:
> query = Query('Person')
> query.update({'name =': 'Ryan', 'age >=': 21})
The supported operators are =, >, <, >=, and <=. Only one inequality filter may be used per query. Any number of equals filters may be used in a single Query.
A filter value may be a list or tuple of values. This is interpreted as
multiple filters with the same filter string and different values, all ANDed
together. For example, this query returns everyone with the tags "google"
and "app engine":
> Query('Person', {'tag =': ('google', 'app engine')})
Result entities can be returned in different orders. Use the Order()
method to specify properties that results will be sorted by, and in which
direction.
Note that filters and orderings may be provided at any time before the query
is run. When the query is fully specified, Run()
runs the query and returns
an iterator. The query results can be accessed through the iterator.
A query object may be reused after it's been run. Its filters and orderings can be changed to create a modified query.
If you know how many result entities you need, use Get()
to fetch them:
> query = Query('Person', {'age >': 21})
> for person in query.Get(4):
> print 'I have four pints left. Have one on me, %s!' % person['name']
If you don't know how many results you need, or if you need them all, you can get an iterator over the results by calling Run():
> for person in Query('Person', {'age >': 21}).Run():
> print 'Have a pint on me, %s!' % person['name']
Get()
is more efficient than Run()
, so use Get()
whenever possible.
Finally, the Count()
method returns the number of result entities matched by
the query. The returned count is cached; successive Count()
calls will not
re-scan the datastore unless the query is changed.
Args | |
---|---|
namespace
|
string, the namespace to query. |
kind
|
string, the kind of entities to query, or None. |
filters
|
dict, initial set of filters. |
keys_only
|
boolean, if keys should be returned instead of entities. |
projection
|
iterable of property names to project. |
distinct
|
boolean, if projection should be distinct. |
compile
|
boolean, if the query should generate cursors. |
cursor
|
datastore_query.Cursor, the start cursor to use. |
end_cursor
|
datastore_query.Cursor, the end cursor to use. |
_namespace
|
deprecated, use namespace instead. |
Methods
Ancestor
Ancestor(
ancestor
)
Sets an ancestor for this query.
This restricts the query to only return result entities that are descended from a given entity. In other words, all of the results will have the ancestor as their parent, or parent's parent, or etc.
Raises BadArgumentError
or BadKeyError
if parent is not an existing
Entity or Key in the datastore.
Args | |
---|---|
the key must be complete |
|
ancestor
|
Entity or Key |
Returns | |
---|---|
this queryQuery |
Count
Count(
limit=1000, **kwargs
)
Returns the number of entities that this query matches.
Args | |
---|---|
limit, a number or None. If there are more results than this, stop short and just return this number. Providing this argument makes the count operation more efficient. | |
config
|
Optional Configuration to use for this request. |
Returns | |
---|---|
The number of results. |
Get
Get(
limit, offset=0, **kwargs
)
Deprecated, use list(Run(...))
instead.
Args | |
---|---|
limit
|
int or long representing the maximum number of entities to return. |
offset
|
int or long representing the number of entities to skip |
kwargs
|
Any keyword arguments accepted by datastore_query.QueryOptions(). |
Returns | |
---|---|
a list of entities[Entity, ...] |
GetBatcher
GetBatcher(
config=None
)
Runs this query and returns a datastore_query.Batcher.
This is not intended to be used by application developers. Use Get()
instead!
Args | |
---|---|
config
|
Optional Configuration to use for this request. |
Returns | |
---|---|
an iterator that provides access to the query resultsIterator |
GetCompiledCursor
GetCompiledCursor()
Get the cursor from the last run of this query.
The source of this cursor varies depending on what the last call was:
- Run: A cursor that points immediately after the last result pulled off the returned iterator.
- Get: A cursor that points immediately after the last result in the returned list.
- Count: A cursor that points immediately after the last result counted.
Returns | |
---|---|
A datastore_query.Cursor object that can be used in subsequent query requests. |
Raises | |
---|---|
AssertionError
|
The query has not yet been run or cannot be compiled. |
GetCompiledQuery
GetCompiledQuery()
Returns the internal-only pb representation of the last query run.
Do not use.
Raises | |
---|---|
AssertionError
|
Query not compiled or not yet executed. |
GetCursor
GetCursor()
Get the cursor from the last run of this query.
The source of this cursor varies depending on what the last call was:
- Run: A cursor that points immediately after the last result pulled off the returned iterator.
- Get: A cursor that points immediately after the last result in the returned list.
- Count: A cursor that points immediately after the last result counted.
Returns | |
---|---|
A datastore_query.Cursor object that can be used in subsequent query requests. |
Raises | |
---|---|
AssertionError
|
The query has not yet been run or cannot be compiled. |
GetDistinct
GetDistinct()
Returns True
if the current instance is distinct.
Returns | |
---|---|
A boolean indicating if the distinct flag is set. |
GetFilterPredicate
GetFilterPredicate()
Returns a datastore_query.FilterPredicate for the current instance.
Returns | |
---|---|
datastore_query.FilterPredicate or None if no filters are set on the current Query. |
GetIndexList
GetIndexList()
Get the index list from the last run of this query.
Returns | |
---|---|
A list of indexes used by the last run of this query. |
Raises | |
---|---|
AssertionError
|
The query has not yet been run. |
GetOrder
GetOrder()
Gets a datastore_query.Order for the current instance.
Returns | |
---|---|
datastore_query.Order or None if there are no sort orders set on the current Query. |
GetQuery
GetQuery()
Returns a datastore_query.Query for the current instance.
GetQueryOptions
GetQueryOptions()
Returns a datastore_query.QueryOptions for the current instance.
Hint
Hint(
hint
)
Sets a hint for how this query should run.
The query hint gives us information about how best to execute your query. Currently, we can only do one index scan, so the query hint should be used to indicates which index we should scan against.
Use FILTER_FIRST if your first filter will only match a few results. In this case, it will be most efficient to scan against the index for this property, load the results into memory, and apply the remaining filters and sort orders there.
Similarly, use ANCESTOR_FIRST if the query's ancestor only has a few descendants. In this case, it will be most efficient to scan all entities below the ancestor and load them into memory first.
Use ORDER_FIRST if the query has a sort order and the result set is large or you only plan to fetch the first few results. In that case, we shouldn't try to load all of the results into memory; instead, we should scan the index for this property, which is in sorted order.
Note that hints are currently ignored in the v3 datastore!
Arg | |
---|---|
one of datastore.Query.[ORDER_FIRST, ANCESTOR_FIRST, FILTER_FIRST] |
Returns | |
---|---|
this queryQuery |
IsKeysOnly
IsKeysOnly()
Returns True
if this query is keys only, False
otherwise.
Order
Order(
*orderings
)
Specify how the query results should be sorted.
Result entities will be sorted by the first property argument, then by the second, and so on. For example, this:
> query = Query('Person')
> query.Order('bday', ('age', Query.DESCENDING))
sorts everyone in order of their birthday, starting with January 1. People with the same birthday are sorted by age, oldest to youngest.
The direction for each sort property may be provided; if omitted, it defaults to ascending.
Order()
may be called multiple times. Each call resets the sort order
from scratch.
If an inequality filter exists in this Query it must be the first property passed to Order. Any number of sort orders may be used after the inequality filter property. Without inequality filters, any number of filters with different orders may be specified.
Entities with multiple values for an order property are sorted by their lowest value.
Note that a sort order implies an existence filter! In other words, Entities without the sort order property are filtered out, and not included in the query results.
If the sort order property has different types in different entities - ie, if bob['id'] is an int and fred['id'] is a string - the entities will be grouped first by the property type, then sorted within type. No attempt is made to compare property values across types.
Raises BadArgumentError
if any argument is of the wrong format.
Args | |
---|---|
the properties to sort by, in sort order. each argument may be either astring or
|
Returns | |
---|---|
this queryQuery |
Run
Run(
**kwargs
)
Runs this query.
If a filter string is invalid, raises BadFilterError
. If a filter value is
invalid, raises BadValueError
. If an IN
filter is provided, and a sort
order on another property is provided, raises BadQueryError
.
If you know in advance how many results you want, use limit=#. It's more efficient.
Args | |
---|---|
kwargs
|
Any keyword arguments accepted by datastore_query.QueryOptions(). |
Returns | |
---|---|
an iterator that provides access to the query resultsIterator |
clear
clear()
D.clear() -> None. Remove all items from D.
copy
copy()
The copy method is not supported.
fromkeys
fromkeys(
value, /
)
Create a new dictionary with keys from iterable and values set to value.
get
get(
key, default, /
)
Return the value for key if key is in the dictionary, else default.
items
items()
D.items() -> a set-like object providing a view on D's items
keys
keys()
D.keys() -> a set-like object providing a view on D's keys
pop
pop()
D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
If the key is not found, return the default if given; otherwise, raise a KeyError.
popitem
popitem()
Remove and return a (key, value) pair as a 2-tuple.
Pairs are returned in LIFO (last-in, first-out) order. Raises KeyError if the dict is empty.
setdefault
setdefault(
filter, value
)
If the filter exists, returns its value. Otherwise sets it to value.
If the property name is the empty string or not a string, raises
BadPropertyError
. If the value is not a supported type, raises
BadValueError
.
update
update(
other
)
Updates this query's filters from the ones in other.
If any filter string is invalid, raises BadFilterError
. If any value is
not a supported type, raises BadValueError
.
values
values()
D.values() -> an object providing a view on D's values
__contains__
__contains__(
key, /
)
True if the dictionary has the specified key, else False.
__eq__
__eq__(
value, /
)
Return self==value.
__ge__
__ge__(
value, /
)
Return self>=value.
__getitem__
__getitem__()
x.getitem(y) <==> x[y]
__gt__
__gt__(
value, /
)
Return self>value.
__iter__
__iter__()
Implement iter(self).
__le__
__le__(
value, /
)
Return self<=value.
__len__
__len__()
Return len(self).
__lt__
__lt__(
value, /
)
Return self<value.
__ne__
__ne__(
value, /
)
Return self!=value.
__or__
__or__(
value, /
)
Return self|value.
__ror__
__ror__(
value, /
)
Return value|self.