feat: define repository for the Variable entity

src/backend/base/langflow/services/database/models/variable/repo.py

@@ -0,0 +1,31 @@
+from typing import List, Optional
+from sqlmodel import select
+from langflow.services.database.models.variable import Variable
+from langflow.services.database.models.repo import AbstractRepository
+
+
+class VariableRepository(AbstractRepository):
+    def add(self, entity: Variable) -> Variable:
+        self.session.add(entity)
+        self.session.commit()
+        self.session.refresh(entity)
+        return entity
+
+    def get(self, id: int) -> Optional[Variable]:
+        return self.session.get(Variable, id)
+
+    def list(self) -> List[Variable]:
+        query = select(Variable)
+        return list(self.session.exec(query).all())
+
+    def update(self, entity: Variable) -> Variable:
+        self.session.add(entity)
+        self.session.commit()
+        self.session.refresh(entity)
+        return entity
+
+    def delete(self, id: int) -> None:
+        entity = self.get(id)
+        if entity:
+            self.session.delete(entity)
+            self.session.commit()