Datastore Metadata

Firestore in Datastore mode provides access to metadata that includes information about entity groups, namespaces, entity kinds, properties, and property representations for each property. You can use metadata, for example, to build a custom datastore viewer for your application or for backend administrative functions.

The Datastore Dashboard in the Google Cloud console also provides some metadata about your application, but the data displayed there differs in some important respects from that returned by these functions.

• Freshness. Reading metadata using the API gets current data, whereas data in the dashboard is updated only once daily.
• Contents. Some metadata in the dashboard is not available through the APIs; the reverse is also true.
• Speed. Metadata gets and queries are billed in the same way as datastore gets and queries. Metadata queries that fetch information on namespaces, kinds, and properties are generally slow to execute. As a rule of thumb, expect a metadata query that returns N entities to take about the same time as N ordinary queries each returning a single entity. Furthermore, property representation queries (non-keys-only property queries) are slower than keys-only property queries. Metadata gets of entity group metadata are somewhat faster than getting a regular entity.

Metadata queries

Three special entity kinds are reserved for metadata queries:

Entity	Description
__namespace__	Used to find all the namespaces used in your application entities.
__kind__	Used to query a specific kind.
__property__	Used to query by a property of a kind.

These kinds will not conflict with others of the same names that may already exist in your application. By querying on these special kinds, you can retrieve entities containing the desired metadata.

The entities returned by metadata queries are generated dynamically, based on the current state of your database. While you can create local entity objects of kinds __namespace__, __kind__, or __property__, any attempt to store them in the database will fail.

Namespace queries

You can use a namespace query to find all namespaces used in the application's entities. This allows you to perform activities such as administrative functions across multiple namespaces.

Namespace queries return entities of the special kind __namespace__ whose key name is the name of a namespace. (An exception is the default namespace designated by the empty string "": since the empty string is not a valid key name, this namespace is keyed with the numeric ID 1 instead.) Queries of this type support filtering only for ranges over the special pseudoproperty __key__, whose value is the entity's key. The results can be sorted by ascending (but not descending) __key__ value. Because __namespace__ entities have no properties, both keys-only and non-keys-only queries return the same information.

The following example returns a list of an application's namespaces in the range between the values assigned to the startNamespace and endNamespace variables:

C#

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore C# API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

KeyFactory keyFactory = _db.CreateKeyFactory("__namespace__");
// List all the namespaces between a lower and upper bound.
string lowerBound = _db.NamespaceId.Substring(0,
    _db.NamespaceId.Length - 1);
string upperBound = _db.NamespaceId + "z";
Key startNamespace = keyFactory.CreateKey(lowerBound);
Key endNamespace = keyFactory.CreateKey(upperBound);
Query query = new Query("__namespace__")
{
    Filter = Filter.And(
        Filter.GreaterThan("__key__", startNamespace),
        Filter.LessThan("__key__", endNamespace))
};
var namespaces = new List<string>();
foreach (Entity entity in _db.RunQuery(query).Entities)
{
    namespaces.Add(entity.Key.Path[0].Name);
};

Go

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Go API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

func metadataNamespaces(w io.Writer, projectID string) error {
	// projectID := "my-project"

	ctx := context.Background()
	client, err := datastore.NewClient(ctx, projectID)
	if err != nil {
		return fmt.Errorf("datastore.NewClient: %w", err)
	}
	defer client.Close()

	start := datastore.NameKey("__namespace__", "g", nil)
	end := datastore.NameKey("__namespace__", "h", nil)
	query := datastore.NewQuery("__namespace__").
		FilterField("__key__", ">=", start).
		FilterField("__key__", "<", end).
		KeysOnly()
	keys, err := client.GetAll(ctx, query, nil)
	if err != nil {
		return fmt.Errorf("client.GetAll: %w", err)
	}

	fmt.Fprintln(w, "Namespaces:")
	for _, k := range keys {
		fmt.Fprintf(w, "\t%v", k.Name)
	}
	return nil
}

Java

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Java API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

KeyFactory keyFactory = datastore.newKeyFactory().setKind("__namespace__");
Key startNamespace = keyFactory.newKey("g");
Key endNamespace = keyFactory.newKey("h");
Query<Key> query =
    Query.newKeyQueryBuilder()
        .setKind("__namespace__")
        .setFilter(
            CompositeFilter.and(
                PropertyFilter.gt("__key__", startNamespace),
                PropertyFilter.lt("__key__", endNamespace)))
        .build();
List<String> namespaces = new ArrayList<>();
QueryResults<Key> results = datastore.run(query);
while (results.hasNext()) {
  namespaces.add(results.next().getName());
}

Node.js

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Node.js API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

async function runNamespaceQuery(startNamespace, endNamespace) {
  const startKey = datastore.key(['__namespace__', startNamespace]);
  const endKey = datastore.key(['__namespace__', endNamespace]);

  const query = datastore
    .createQuery('__namespace__')
    .select('__key__')
    .filter(
      and([
        new PropertyFilter('__key__', '>=', startKey),
        new PropertyFilter('__key__', '<', endKey),
      ])
    );

  const [entities] = await datastore.runQuery(query);
  const namespaces = entities.map(entity => entity[datastore.KEY].name);

  console.log('Namespaces:');
  namespaces.forEach(namespace => console.log(namespace));

  return namespaces;
}

PHP

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore PHP API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

$query = $datastore->query()
    ->kind('__namespace__')
    ->projection(['__key__'])
    ->filter('__key__', '>=', $datastore->key('__namespace__', $start))
    ->filter('__key__', '<', $datastore->key('__namespace__', $end));
$result = $datastore->runQuery($query);
/* @var array<string> $namespaces */
$namespaces = [];
foreach ($result as $namespace) {
    $namespaces[] = $namespace->key()->pathEnd()['name'];
}

Python

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Python API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

from google.cloud import datastore

# For help authenticating your client, visit
# https://cloud.google.com/docs/authentication/getting-started
client = datastore.Client()

# All namespaces
query = client.query(kind="__namespace__")
query.keys_only()

all_namespaces = [entity.key.id_or_name for entity in query.fetch()]

# Filtered namespaces
start_namespace = client.key("__namespace__", "g")
end_namespace = client.key("__namespace__", "h")
query = client.query(kind="__namespace__")
query.key_filter(start_namespace, ">=")
query.key_filter(end_namespace, "<")

filtered_namespaces = [entity.key.id_or_name for entity in query.fetch()]

Ruby

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Ruby API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

query = datastore.query("__namespace__")
                 .select("__key__")
                 .where("__key__", ">=", datastore.key("__namespace__", "g"))
                 .where("__key__", "<", datastore.key("__namespace__", "h"))

namespaces = datastore.run(query).map do |entity|
  entity.key.name
end

GQL

SELECT __key__ FROM __namespace__
WHERE __key__ >= KEY(__namespace__, 'namespace-a')
  AND __key__ <  KEY(__namespace__, 'namespace-b')

Kind queries

Kind queries return entities of kind __kind__ whose key name is the name of an entity kind. Queries of this type are implicitly restricted to the current namespace and support filtering only for ranges over the __key__ pseudoproperty. The results can be sorted by ascending (but not descending) __key__ value. Because __kind__ entities have no properties, both keys-only and non-keys-only queries return the same information.

The following example prints a list of the kinds used in an application:

C#

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore C# API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Query query = new Query("__kind__");
var kinds = new List<string>();
foreach (Entity entity in _db.RunQuery(query).Entities)
{
    kinds.Add(entity.Key.Path[0].Name);
};

Go

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Go API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

query := datastore.NewQuery("__kind__").KeysOnly()
keys, err := client.GetAll(ctx, query, nil)
if err != nil {
	log.Fatalf("client.GetAll: %v", err)
}

kinds := make([]string, 0, len(keys))
for _, k := range keys {
	kinds = append(kinds, k.Name)
}

Java

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Java API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Query<Key> query = Query.newKeyQueryBuilder().setKind("__kind__").build();
List<String> kinds = new ArrayList<>();
QueryResults<Key> results = datastore.run(query);
while (results.hasNext()) {
  kinds.add(results.next().getName());
}

Node.js

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Node.js API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

async function runKindQuery() {
  const query = datastore.createQuery('__kind__').select('__key__');

  const [entities] = await datastore.runQuery(query);
  const kinds = entities.map(entity => entity[datastore.KEY].name);

  console.log('Kinds:');
  kinds.forEach(kind => console.log(kind));

  return kinds;
}

PHP

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore PHP API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

$query = $datastore->query()
    ->kind('__kind__')
    ->projection(['__key__']);
$result = $datastore->runQuery($query);
/* @var array<string> $kinds */
$kinds = [];
foreach ($result as $kind) {
    $kinds[] = $kind->key()->pathEnd()['name'];
}

Python

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Python API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

from google.cloud import datastore

# For help authenticating your client, visit
# https://cloud.google.com/docs/authentication/getting-started
client = datastore.Client()

query = client.query(kind="__kind__")
query.keys_only()

kinds = [entity.key.id_or_name for entity in query.fetch()]

Ruby

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Ruby API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

query = datastore.query("__kind__")
                 .select("__key__")

kinds = datastore.run(query).map do |entity|
  entity.key.name
end

GQL

SELECT __key__ FROM __kind__

Property queries

Property queries return entities of kind __property__ denoting the indexed properties associated with an entity kind. (Unindexed properties are not included.) The entity representing property p of kind k is built as follows:

• The entity's key has kind __property__ and key name p.
• The entity's parent key has kind __kind__ and key name k.
• The entity's property_representation array property contains all the property's representations.

For example, if your database contains exactly two Task entities with name and done properties:

Key: 'Task:1'
name: 'Read some properties'
done: true

Key: 'Task:2'
name: 'Climb'
done: null

then the two entities returned by a __property__ query will be:

Key: '__kind__:Task/__property__:name'
property_representation: [ 'STRING' ]

Key: '__kind__:Task/__property__:done'
property_representation: [ 'BOOLEAN', 'NULL' ]

Property queries are implicitly restricted to the current namespace, and support limited filtering with an ancestor or a range over the __key__ pseudoproperty.

A keys-only property query is more efficient than a non-keys-only query, as it does not need to collect the property's representations. The following example retrieves the names of all of an application's entity kinds and the properties associated with each:

C#

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore C# API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Query query = new Query("__property__");
var properties = new List<string>();
foreach (Entity entity in _db.RunQuery(query).Entities)
{
    string kind = entity.Key.Path[0].Name;
    string property = entity.Key.Path[1].Name;
    if (kind == "Task")
        properties.Add(property);
};

Go

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Go API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

query := datastore.NewQuery("__property__").KeysOnly()
keys, err := client.GetAll(ctx, query, nil)
if err != nil {
	log.Fatalf("client.GetAll: %v", err)
}

props := make(map[string][]string) // Map from kind to slice of properties.
for _, k := range keys {
	prop := k.Name
	kind := k.Parent.Name
	props[kind] = append(props[kind], prop)
}

Java

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Java API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Query<Key> query = Query.newKeyQueryBuilder().setKind("__property__").build();
QueryResults<Key> keys = datastore.run(query);
Map<String, Collection<String>> propertiesByKind = new HashMap<>();
while (keys.hasNext()) {
  Key key = keys.next();
  String kind = key.getParent().getName();
  String propertyName = key.getName();
  Collection<String> properties = propertiesByKind.get(kind);
  if (properties == null) {
    properties = new HashSet<>();
    propertiesByKind.put(kind, properties);
  }
  properties.add(propertyName);
}

Node.js

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Node.js API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

async function runPropertyQuery() {
  const query = datastore.createQuery('__property__').select('__key__');
  const [entities] = await datastore.runQuery(query);
  // @TODO convert below object to map
  const propertiesByKind = {};

  entities.forEach(entity => {
    const key = entity[datastore.KEY];
    const kind = key.path[1];
    const property = key.path[3];

    propertiesByKind[kind] = propertiesByKind[kind] || [];
    propertiesByKind[kind].push(property);
  });

  console.log('Properties by Kind:');
  for (const key in propertiesByKind) {
    console.log(key, propertiesByKind[key]);
  }

  return propertiesByKind;
}

PHP

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore PHP API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

$query = $datastore->query()
    ->kind('__property__')
    ->projection(['__key__']);
$result = $datastore->runQuery($query);
/* @var array<string> $properties */
$properties = [];
/* @var Entity $entity */
foreach ($result as $entity) {
    $kind = $entity->key()->path()[0]['name'];
    $propertyName = $entity->key()->path()[1]['name'];
    $properties[] = "$kind.$propertyName";
}

Python

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Python API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

from google.cloud import datastore

# For help authenticating your client, visit
# https://cloud.google.com/docs/authentication/getting-started
client = datastore.Client()

from collections import defaultdict

query = client.query(kind="__property__")
query.keys_only()

properties_by_kind = defaultdict(list)

for entity in query.fetch():
    kind = entity.key.parent.name
    property_ = entity.key.name

    properties_by_kind[kind].append(property_)

Ruby

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Ruby API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

query = datastore.query("__property__")
                 .select("__key__")

entities = datastore.run query
properties_by_kind = entities.each_with_object({}) do |entity, memo|
  kind = entity.key.parent.name
  prop = entity.key.name
  memo[kind] ||= []
  memo[kind] << prop
end

GQL

SELECT __key__ FROM __property__

Property queries: property representations

Non-keys-only property queries, known as property representation queries, return additional information on the value types used for each property. The property_representation property in the entity representing property p of kind k is an array containing all representations of p's value in any entity of kind k.

Each value has the following representation (note that some value types share representations):

Value type	Representation
Integer	INT64
Floating-point number	DOUBLE
Boolean	BOOLEAN
Text string	STRING
Byte string	STRING
Date and time	INT64
Datastore key	REFERENCE
Embedded entity	STRING
Array	representation of the array's elements
Geographical point	POINT
Null	NULL

The following example finds all representations of properties of kind Task, using an ancestor property query:

C#

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore C# API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Key key = _db.CreateKeyFactory("__kind__").CreateKey("Task");
Query query = new Query("__property__")
{
    Filter = Filter.HasAncestor(key)
};
var properties = new List<string>();
foreach (Entity entity in _db.RunQuery(query).Entities)
{
    string kind = entity.Key.Path[0].Name;
    string property = entity.Key.Path[1].Name;
    var representations = entity["property_representation"]
        .ArrayValue.Values.Select(x => x.StringValue)
        .OrderBy(x => x);
    properties.Add($"{property}:" +
        string.Join(",", representations));
};

Go

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Go API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

kindKey := datastore.NameKey("__kind__", "Task", nil)
query := datastore.NewQuery("__property__").Ancestor(kindKey)

type Prop struct {
	Repr []string `datastore:"property_representation"`
}

var props []Prop
keys, err := client.GetAll(ctx, query, &props)

Java

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Java API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Key key = datastore.newKeyFactory().setKind("__kind__").newKey("Task");
Query<Entity> query =
    Query.newEntityQueryBuilder()
        .setKind("__property__")
        .setFilter(PropertyFilter.hasAncestor(key))
        .build();
QueryResults<Entity> results = datastore.run(query);
Map<String, Collection<String>> representationsByProperty = new HashMap<>();
while (results.hasNext()) {
  Entity result = results.next();
  String propertyName = result.getKey().getName();
  List<StringValue> representations = result.getList("property_representation");
  Collection<String> currentRepresentations = representationsByProperty.get(propertyName);
  if (currentRepresentations == null) {
    currentRepresentations = new HashSet<>();
    representationsByProperty.put(propertyName, currentRepresentations);
  }
  for (StringValue value : representations) {
    currentRepresentations.add(value.get());
  }
}

Node.js

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Node.js API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

async function runPropertyByKindQuery() {
  const ancestorKey = datastore.key(['__kind__', 'Account']);

  const query = datastore
    .createQuery('__property__')
    .hasAncestor(ancestorKey);
  const [entities] = await datastore.runQuery(query);

  const representationsByProperty = {};

  entities.forEach(entity => {
    const key = entity[datastore.KEY];
    const propertyName = key.name;
    const propertyType = entity.property_representation;

    representationsByProperty[propertyName] = propertyType;
  });

  console.log('Task property representations:');
  for (const key in representationsByProperty) {
    console.log(key, representationsByProperty[key]);
  }

  return representationsByProperty;
}

PHP

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore PHP API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

$ancestorKey = $datastore->key('__kind__', 'Task');
$query = $datastore->query()
    ->kind('__property__')
    ->hasAncestor($ancestorKey);
$result = $datastore->runQuery($query);
/* @var array<string,string> $properties */
$properties = [];
/* @var Entity $entity */
foreach ($result as $entity) {
    $propertyName = $entity->key()->path()[1]['name'];
    $propertyType = $entity['property_representation'];
    $properties[$propertyName] = $propertyType;
}
// Example values of $properties: ['description' => ['STRING']]

Python

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Python API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

from google.cloud import datastore

# For help authenticating your client, visit
# https://cloud.google.com/docs/authentication/getting-started
client = datastore.Client()

ancestor = client.key("__kind__", "Task")
query = client.query(kind="__property__", ancestor=ancestor)

representations_by_property = {}

for entity in query.fetch():
    property_name = entity.key.name
    property_types = entity["property_representation"]

    representations_by_property[property_name] = property_types

Ruby

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Ruby API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

ancestor_key = datastore.key "__kind__", "Task"
query = datastore.query("__property__")
                 .ancestor(ancestor_key)

entities = datastore.run query
representations = entities.each_with_object({}) do |entity, memo|
  property_name = entity.key.name
  property_types = entity["property_representation"]
  memo[property_name] = property_types
end

GQL

SELECT * FROM __property__
WHERE __key__ HAS ANCESTOR KEY(__kind__, 'Task')

Property queries: filtering

Property queries support ancestor filtering on a __kind__ or __property__ key, to limit the query results to a single kind or property, as seen in the property representation query above.

Property queries can also be filtered with a range over the pseudoproperty __key__, where the keys denote either __kind__ or __property__ entities. The results can be sorted by ascending (but not descending) __key__ value. Filtering is applied to kind-property pairs, ordered first by kind and second by property. For instance, suppose you have entities with these properties:

• kind Task with properties
  • created
  • priority
  • tags
• kind TaskList with properties
  • created

The following keys-only property query:

C#

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore C# API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Key key = _db.CreateKeyFactory("__kind__").CreateKey("Task");
Key startKey = new KeyFactory(key, "__property__")
    .CreateKey("priority");
Query query = new Query("__property__")
{
    Filter = Filter.GreaterThanOrEqual("__key__", startKey)
};
var properties = new List<string>();
foreach (Entity entity in _db.RunQuery(query).Entities)
{
    string kind = entity.Key.Path[0].Name;
    string property = entity.Key.Path[1].Name;
    properties.Add($"{kind}.{property}");
};

Go

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Go API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Not Applicable

Java

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Java API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Key startKey =
    datastore
        .newKeyFactory()
        .setKind("__property__")
        .addAncestors(PathElement.of("__kind__", "Task"))
        .newKey("priority");
Query<Key> query =
    Query.newKeyQueryBuilder()
        .setKind("__property__")
        .setFilter(PropertyFilter.ge("__key__", startKey))
        .build();
Map<String, Collection<String>> propertiesByKind = new HashMap<>();
QueryResults<Key> keys = datastore.run(query);
while (keys.hasNext()) {
  Key key = keys.next();
  String kind = key.getParent().getName();
  String propertyName = key.getName();
  Collection<String> properties = propertiesByKind.get(kind);
  if (properties == null) {
    properties = new HashSet<String>();
    propertiesByKind.put(kind, properties);
  }
  properties.add(propertyName);
}

Node.js

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Node.js API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Not Applicable

PHP

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore PHP API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

$ancestorKey = $datastore->key('__kind__', 'Task');
$startKey = $datastore->key('__property__', 'priority')
    ->ancestorKey($ancestorKey);
$query = $datastore->query()
    ->kind('__property__')
    ->filter('__key__', '>=', $startKey);
$result = $datastore->runQuery($query);
/* @var array<string> $properties */
$properties = [];
/* @var Entity $entity */
foreach ($result as $entity) {
    $kind = $entity->key()->path()[0]['name'];
    $propertyName = $entity->key()->path()[1]['name'];
    $properties[] = "$kind.$propertyName";
}

Python

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Python API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Not Applicable

Ruby

To learn how to install and use the client library for Cloud Datastore, see Cloud Datastore client libraries. For more information, see the Cloud Datastore Ruby API reference documentation.

To authenticate to Cloud Datastore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

start_key = datastore.key [["__kind__", "Task"], ["__property__", "priority"]]
query = datastore.query("__property__")
                 .select("__key__")
                 .where("__key__", ">=", start_key)

entities = datastore.run query
properties_by_kind = entities.each_with_object({}) do |entity, memo|
  kind = entity.key.parent.name
  prop = entity.key.name
  memo[kind] ||= []
  memo[kind] << prop
end

GQL

SELECT __key__ FROM __property__
WHERE __key__ >= KEY(__kind__, 'Task', __property__, 'priority')

will collect the following kind, property name pairs:

Task, priority
Task, tags
TaskList, created

Notice that the results include properties from kinds Task and TaskList, but do not include the created property of kind Task, because it falls outside the range specified for the query.

Note: Since the __key__ kind filters on kind-property pairs, you can't use a single query for the same property name in different kinds. You can query for all properties in all kinds (or in a range of kinds), but you cannot construct a single query that retrieves, for example, all properties with names between m and q in all kinds (or in kinds A and B).