Add method to retrieve a single partial doc

composer.json

@@ -18,7 +18,7 @@
   "require": {
     "php": "^7.1",
     "ext-pdo": "*",
-    "event-engine/php-persistence": "^0.6"
+    "event-engine/php-persistence": "^0.7"
   },
   "require-dev": {
     "roave/security-advisories": "dev-master",

src/PostgresDocumentStore.php

@@ -498,6 +498,31 @@ public function getDoc(string $collectionName, string $docId): ?array
         return json_decode($row, true);
     }
 
+    /**
+     * @inheritDoc
+     */
+    public function getPartialDoc(string $collectionName, PartialSelect $partialSelect, string $docId): ?array
+    {
+        $select = $this->makeSelect($partialSelect);
+
+        $query = <<<EOT
+SELECT $select
+FROM {$this->schemaName($collectionName)}.{$this->tableName($collectionName)}
+WHERE id = :id
+EOT;
+        $stmt = $this->connection->prepare($query);
+
+        $stmt->execute(['id' => $docId]);
+
+        $row = $stmt->fetch(\PDO::FETCH_ASSOC);
+
+        if(!$row) {
+            return null;
+        }
+
+        return $this->transformPartialDoc($partialSelect, $row);
+    }
+
     /**
      * @inheritDoc
      */

tests/PostgresDocumentStoreTest.php

@@ -627,6 +627,72 @@ public function it_finds_partial_docs()
         ], $result[$docCId]);
     }
 
+    /**
+     * @test
+     */
+    public function it_gets_partial_doc_by_id()
+    {
+        $collectionName = 'test_get_partial_doc';
+        $this->documentStore->addCollection($collectionName);
+
+        $docAId = Uuid::uuid4()->toString();
+        $docA = [
+            'some' => [
+                'prop' => 'foo',
+                'other' => [
+                    'nested' => 42
+                ]
+            ],
+            'baz' => 'bat',
+        ];
+        $this->documentStore->addDoc($collectionName, $docAId, $docA);
+
+        $docBId = Uuid::uuid4()->toString();
+        $docB = [
+            'some' => [
+                'prop' => 'bar',
+                'other' => [
+                    'nested' => 43
+                ],
+                //'baz' => 'bat', missing so should be null
+            ],
+        ];
+        $this->documentStore->addDoc($collectionName, $docBId, $docB);
+
+        $docCId = Uuid::uuid4()->toString();
+        $docC = [
+            'some' => [
+                'prop' => 'foo',
+                'other' => [
+                    //'nested' => 42, missing, so should be null
+                    'ignoredNested' => 'value'
+                ]
+            ],
+            'baz' => 'bat',
+        ];
+        $this->documentStore->addDoc($collectionName, $docCId, $docC);
+
+        $partialSelect = new PartialSelect([
+            'some.alias' => 'some.prop', // Nested alias <- Nested field
+            'magicNumber' => 'some.other.nested', // Top level alias <- Nested Field
+            'baz', // Top level field,
+        ]);
+
+        $partialDocA = $this->documentStore->getPartialDoc($collectionName, $partialSelect, $docAId);
+
+        $this->assertEquals([
+            'some' => [
+                'alias' => 'foo',
+            ],
+            'magicNumber' => 42,
+            'baz' => 'bat',
+        ], $partialDocA);
+
+        $partialDocD = $this->documentStore->getPartialDoc($collectionName, $partialSelect, Uuid::uuid4()->toString());
+
+        $this->assertNull($partialDocD);
+    }
+
     /**
      * @test
      */