Added Schema::keep - to keep selected schema entries (#996)

src/core/etl/src/Flow/ETL/Row/Schema.php

@@ -115,6 +115,29 @@ public function gracefulRemove(string|Reference ...$entries) : self
         return $this;
     }
 
+    public function keep(string|Reference ...$entries) : self
+    {
+        $refs = References::init(...$entries);
+
+        $definitions = [];
+
+        foreach ($entries as $entry) {
+            if (!$this->findDefinition($entry)) {
+                throw new SchemaDefinitionNotFoundException((string) $entry);
+            }
+        }
+
+        foreach ($this->definitions as $definition) {
+            if ($refs->has($definition->entry())) {
+                $definitions[] = $definition;
+            }
+        }
+
+        $this->setDefinitions(...$definitions);
+
+        return $this;
+    }
+
     public function merge(self $schema) : self
     {
         $newDefinitions = $this->definitions;

src/core/etl/tests/Flow/ETL/Tests/Unit/Row/SchemaTest.php

@@ -116,6 +116,36 @@ public function test_graceful_remove_non_existing_definition() : void
         );
     }
 
+    public function test_keep_non_existing_entries() : void
+    {
+        $this->expectException(SchemaDefinitionNotFoundException::class);
+
+        schema(
+            int_schema('id'),
+            str_schema('name'),
+            str_schema('surname'),
+            str_schema('email'),
+        )->keep('not-existing');
+    }
+
+    public function test_keep_selected_entries() : void
+    {
+        $schema = schema(
+            int_schema('id'),
+            str_schema('name'),
+            str_schema('surname'),
+            str_schema('email'),
+        );
+
+        $this->assertEquals(
+            schema(
+                str_schema('name'),
+                str_schema('surname'),
+            ),
+            $schema->keep('name', 'surname')
+        );
+    }
+
     public function test_making_whole_schema_nullable() : void
     {
         $schema = new Schema(