Created an extendable declarative base class

... for mlwh ORM classes so that common methods can be
implemented.

Customised __repr__ method for one of db classes.

lang_qc/db/mlwh_schema.py

@@ -25,9 +25,30 @@
 from sqlalchemy.dialects.mysql import SMALLINT as mysqlSMALLINT
 from sqlalchemy.dialects.mysql import TINYINT as mysqlTINYINT
 from sqlalchemy.dialects.mysql import VARCHAR as mysqlVARCHAR
-from sqlalchemy.orm import declarative_base, relationship
+from sqlalchemy.orm import DeclarativeBase, relationship
 
-Base = declarative_base()
+
+class Base(DeclarativeBase):
+    """
+    A base class for declarative class definitions for the ml warehouse database.
+    """
+
+    def get_row_description(self, fields: list[str]) -> str:
+        """
+        Returns a printable representation of the database table row. Interprets
+        a list of strings given as the `fields` argument as a list of column
+        names. Combines the name of the class, names of the given columns
+        and respective values into a row description. The columns for which
+        the row has a NULL value are omitted from the description.
+        """
+
+        pairs = []
+        for name in fields:
+            value = self.__getattribute__(name)
+            if value is not None:
+                pairs.append(f"{name}={value}")
+        description = ", ".join(pairs)
+        return f"{self.__module__}.{self.__class__.__name__}: {description}"
 
 
 class Sample(Base):
@@ -538,7 +559,16 @@ class PacBioRunWellMetrics(Base):
         "PacBioProductMetrics", back_populates="pac_bio_run_well_metrics"
     )
 
-    def get_experiment_info(self):
+    """Custom or customised methods are added below"""
+
+    def __repr__(self):
+        """Returns a printable representation of the database row"""
+
+        return self.get_row_description(
+            ["pac_bio_run_name", "well_label", "plate_number", "id_pac_bio_product"]
+        )
+
+    def get_experiment_info(self) -> list[PacBioRun]:
         """Returns a list of PacBioRun mlwh database rows.
 
         Returns LIMS information about the PacBio experiment

tests/test_mlwh_db_classes.py

@@ -0,0 +1,24 @@
+from sqlalchemy import select
+
+from lang_qc.db.mlwh_schema import PacBioRunWellMetrics
+
+"""Tests for custom and customised ORM methods"""
+
+
+def test_pac_bio_well_metrics_repr(mlwhdb_test_session, mlwhdb_load_runs):
+    id1 = "cf18bd66e0f0895ea728c1d08103c62d3de8a57a5f879cee45f7b0acc028aa61"
+    id2 = "513c674f489b106c6af716dd0d210826ff03b7648d50888839c3722ca1b10dbf"
+    data = {
+        id1: f"pac_bio_run_name=TRACTION-RUN-92, well_label=A1, id_pac_bio_product={id1}",
+        id2: f"pac_bio_run_name=TRACTION-RUN-1140, well_label=A1, plate_number=2, id_pac_bio_product={id2}",
+    }
+
+    for id in data.keys():
+        query = select(PacBioRunWellMetrics).where(
+            PacBioRunWellMetrics.id_pac_bio_product == id
+        )
+        db_row = mlwhdb_test_session.execute(query).scalar_one()
+        assert (
+            db_row.__repr__()
+            == "lang_qc.db.mlwh_schema.PacBioRunWellMetrics: " + data[id]
+        )