orm: Add SELECT generation

opdb/db/__init__.py

@@ -16,5 +16,4 @@
 Database management
 """
 
-from . import models, orm  # noqa
 from .db import Db  # noqa

opdb/db/db.py

@@ -50,11 +50,10 @@ class Db:
         """
         Returns the last snapshot of the given IRI.
         """
-        with self.conn.cursor(
-            row_factory=psycopg.rows.class_row(models.WebPageSnapshot)
-        ) as cur:
-            cur.execute("SELECT * FROM web_page_snapshot WHERE url=%s", (url,))
-            return cur.fetchone()
+        snapshots = models.WebPageSnapshot.select(
+            self.conn, "WHERE url=%s ORDER BY snapshot_date DESC LIMIT 1", (url,)
+        )
+        return next(snapshots, None)
 
     def add_web_page_snapshots(
         self, snapshots: typing.Iterable[models.WebPageSnapshot]

opdb/db/orm.py

@@ -137,6 +137,17 @@ class BaseModel:
                     )
                     copy.write_row(row)
 
+    @classmethod
+    def select(
+        cls: type[_TSelf], conn: psycopg.Connection, clauses: str, params: tuple
+    ) -> typing.Iterator[_TSelf]:
+        """
+        Selects objects from the corresponding table and yields instances of this class.
+        """
+        with conn.cursor(row_factory=psycopg.rows.class_row(cls)) as cur:
+            cur.execute(f"SELECT * FROM {cls.TABLE} {clauses}", params)
+            yield from cur
+
     @classmethod
     def db_schema(cls) -> str:
         """