Add Firestore distributed counter snippets (GoogleCloudPlatform#2412)

* Add samples for distributed counters

* Refactor list building

* Excess instance

* Empty line delete

* Empty lines delete

* Make comments more detailed.

* Fix line too long

* Move distributed counter samples and tests into separate files.

* Blank lines fix.

* Add firestore.Client

* Test prefix.

* Add fixture.

* Line too long fix.

* Line too long fix.

* Update firestore/cloud-client/distributed_counters.py

Co-Authored-By: Brad Miro <[email protected]>

* Update firestore/cloud-client/distributed_counters_test.py

Co-Authored-By: Brad Miro <[email protected]>

* Update firestore/cloud-client/distributed_counters_test.py

Co-Authored-By: Brad Miro <[email protected]>

* Update firestore/cloud-client/distributed_counters_test.py

Co-Authored-By: Brad Miro <[email protected]>

Author: 2 people

firestore/cloud-client/distributed_counters.py

@@ -0,0 +1,77 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# [START fs_counter_classes]
+import random
+
+from google.cloud import firestore
+
+
+class Shard(object):
+    """
+    A shard is a distributed counter. Each shard can support being incremented
+    once per second. Multiple shards are needed within a Counter to allow
+    more frequent incrementing.
+    """
+
+    def __init__(self):
+        self._count = 0
+
+    def to_dict(self):
+        return {"count": self._count}
+
+
+class Counter(object):
+    """
+    A counter stores a collection of shards which are
+    summed to return a total count. This allows for more
+    frequent incrementing than a single document.
+    """
+
+    def __init__(self, num_shards):
+        self._num_shards = num_shards
+# [END fs_counter_classes]
+
+    # [START fs_create_counter]
+    def init_counter(self, doc_ref):
+        """
+        Create a given number of shards as
+        subcollection of specified document.
+        """
+        col_ref = doc_ref.collection("shards")
+
+        # Initialize each shard with count=0
+        for num in range(self._num_shards):
+            shard = Shard()
+            col_ref.document(str(num)).set(shard.to_dict())
+    # [END fs_create_counter]
+
+    # [START fs_increment_counter]
+    def increment_counter(self, doc_ref):
+        """Increment a randomly picked shard."""
+        doc_id = random.randint(0, self._num_shards - 1)
+
+        shard_ref = doc_ref.collection("shards").document(str(doc_id))
+        return shard_ref.update({"count": firestore.Increment(1)})
+    # [END fs_increment_counter]
+
+    # [START fs_get_count]
+    def get_count(self, doc_ref):
+        """Return a total count across all shards."""
+        total = 0
+        shards = doc_ref.collection("shards").list_documents()
+        for shard in shards:
+            total += shard.get().to_dict().get("count", 0)
+        return total
+    # [END fs_get_count]

firestore/cloud-client/distributed_counters_test.py

@@ -0,0 +1,49 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google.cloud import firestore
+import pytest
+
+import distributed_counters
+
+
+shards_list = []
+doc_ref = None
+
+
+@pytest.fixture
+def fs_client():
+    yield firestore.Client()
+
+    # clean up
+    for shard in shards_list:
+        shard.delete()
+
+    if doc_ref:
+        doc_ref.delete()
+
+
+def test_distributed_counters(fs_client):
+    col = fs_client.collection("dc_samples")
+    doc_ref = col.document("distributed_counter")
+    counter = distributed_counters.Counter(2)
+    counter.init_counter(doc_ref)
+
+    shards = doc_ref.collection("shards").list_documents()
+    shards_list = [shard for shard in shards]
+    assert len(shards_list) == 2
+
+    counter.increment_counter(doc_ref)
+    counter.increment_counter(doc_ref)
+    assert counter.get_count(doc_ref) == 2