Table extensions examples

docs/dev/explanations/extensions.md

@@ -78,13 +78,14 @@ To develop, follow the same [instruction as `diracx`](../tutorials/getting-start
 
 The `gubbins-db` package contains the extension for the DB.
 
-### New DB
+### New SQL DB
 
 `lollygagDB` is a DB which is specific to `gubbins`, i.e. it does not modify or extend an existing `diracx` db
 
-### Extended DB
+### Extended SQL DB
 
-`GubbinsJobDB` illustrates how to extend an existing `diracx` DB, add new methods, modify methods, add a table.
+`GubbinsJobDB` illustrates how to extend an existing `diracx` SQL DB, add new methods, modify methods, add a table, adding a column to one table.
+Modifying an existing column is instead not supported.
 
 A router test exists (`test_gubbins_job_manager.py`), even though no router is redefined. It is just to show that the correct DB is being loaded.
 

extensions/gubbins/gubbins-db/src/gubbins/db/sql/jobs/schema.py

@@ -1,14 +1,29 @@
 from diracx.db.sql.job.db import JobDBBase
-from diracx.db.sql.job.schema import str255
+from diracx.db.sql.job.schema import InputData, str255
 from sqlalchemy import ForeignKey
 from sqlalchemy.orm import Mapped, mapped_column
 
 
-# You need to inherit from the DeclarativeBase of the parent DB
+# GubbinsInputData: Extends InputData by ADDING a column
+# NOTE: Simple inheritance works here because we're ADDING a new column,
+# not modifying an existing one. This is the preferred approach when possible.
+class GubbinsInputData(InputData):
+    """Extended InputData table with Adler checksum support"""
+
+    __tablename__ = "InputData"
+    __table_args__ = {"extend_existing": True}
+
+    # New column for Adler checksum
+    adler_checksum: Mapped[str255] = mapped_column("AdlerChecksum", default="")
+
+
+# Example of defining a new table
+# NOTE: You need to inherit from the DeclarativeBase of the parent DB
 class GubbinsInfo(JobDBBase):
     """An extra table with respect to Vanilla diracx JobDB"""
 
-    __tablename__ = "GubbinsJobs"
+    __tablename__ = "GubbinsInfo"
+    __table_args__ = {"extend_existing": True}
 
     job_id: Mapped[int] = mapped_column(
         "JobID", ForeignKey("Jobs.JobID", ondelete="CASCADE"), primary_key=True