Implement countDocs from DocumentStore interface

This implements the countDoc feature from the DocumentStore interface so
it can be used together with the latest version of the DocumentStore.

This allows top retrieve the number of affected documents without
having to actually retrieve all the documents.

Author: heiglandreas

src/PostgresDocumentStore.php

@@ -524,6 +524,29 @@ public function filterDocs(string $collectionName, Filter $filter, int $skip = n
         }
     }
 
+    /**
+     * @param string $collectionName
+     * @param Filter $filter
+     * @return int number of docs
+     */
+    public function countDocs(string $collectionName, Filter $filter): int
+    {
+        [$filterStr, $args] = $this->filterToWhereClause($filter);
+
+        $where = $filterStr? "WHERE $filterStr" : '';
+
+        $query = <<<EOT
+SELECT count(doc) 
+FROM {$this->schemaName($collectionName)}.{$this->tableName($collectionName)}
+$where;
+EOT;
+        $stmt = $this->connection->prepare($query);
+
+        $stmt->execute($args);
+
+        return (int) $stmt->fetchColumn(0);
+    }
+
     private function transactional(callable $callback)
     {
         if($this->manageTransactions) {

tests/PostgresDocumentStoreTest.php

@@ -434,6 +434,32 @@ public function it_handles_not_filter_nested_in_and_filter()
         $this->assertEquals([$thirdDocId], $refs);
     }
 
+    /**
+     * @test
+     */
+    public function it_counts_any_of_filter()
+    {
+        $collectionName = 'test_any_of_filter';
+        $this->documentStore->addCollection($collectionName);
+
+        $doc1 = ["foo" => "bar"];
+        $doc2 = ["foo" => "baz"];
+        $doc3 = ["foo" => "bat"];
+
+        $docs = [$doc1, $doc2, $doc3];
+
+        array_walk($docs, function (array $doc) use ($collectionName) {
+            $this->documentStore->addDoc($collectionName, Uuid::uuid4()->toString(), $doc);
+        });
+
+        $count = $this->documentStore->countDocs(
+            $collectionName,
+            new AnyOfFilter("foo", ["bar", "bat"])
+        );
+
+        $this->assertSame(2, $count);
+    }
+
     private function getIndexes(string $collectionName): array
     {
         return TestUtil::getIndexes($this->connection, self::TABLE_PREFIX.$collectionName);