Merge pull request #29 from hsf-training/conditions-database-example

Conditions database example

_episodes/11-conditions-database.md

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+---
+title: "Conditions Database Example Using SQLAlchemy"
+teaching: x
+exercises: x
+questions:
+- ""
+- ""
+objectives:
+- ""
+- ""
+keypoints:
+- ""
+- ""
+---
+
+
+
+# Conditions Database Example Using SQLAlchemy
+
+This lesson demonstrates how to create a simple Conditions Database using SQLAlchemy in Python.
+We will define three tables: `GlobalTag`, `PayloadType`, and `PayloadIOV`, and establish relationships
+between them. We will then add example data and query the database to retrieve specific entries.
+
+## Imports
+First, we import the necessary modules from SQLAlchemy.
+
+```python
+from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
+from sqlalchemy.orm import declarative_base, sessionmaker, relationship
+## Define ORM Models
+We define our ORM models: `GlobalTag`, `PayloadType`, and `PayloadIOV`, along with the necessary relationships.
+
+from sqlalchemy.sql import func, and_
+```
+## Database Connection
+Next, we define the MySQL database connection URL and create an SQLAlchemy engine, session, and declarative base.
+
+```python
+# Define the MySQL database connection URL
+db_url = "mysql+pymysql://root:pass@localhost:3306/cdb"
+
+# Create an SQLAlchemy engine
+engine = create_engine(db_url)
+Session = sessionmaker(bind=engine)
+session = Session()
+Base = declarative_base()
+```
+## Define Tables
+We define all the tables in the database.
+
+```python
+class GlobalTag(Base):
+    __tablename__ = "GlobalTag"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(255), unique=True, nullable=False)
+
+    # Relationship to PayloadType
+    payload_types = relationship("PayloadType", back_populates="global_tag")
+
+class PayloadType(Base):
+    __tablename__ = "PayloadType"
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(255), unique=True, nullable=False)
+    global_tag_id = Column(Integer, ForeignKey('GlobalTag.id'))
+
+    # Relationship to GlobalTag and PayloadIOV
+    global_tag = relationship("GlobalTag", back_populates="payload_types")
+    payload_iovs = relationship("PayloadIOV", back_populates="payload_type")
+
+class PayloadIOV(Base):
+    __tablename__ = "PayloadIOV"
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    payload_url = Column(String(255), nullable=False)
+    iov = Column(Integer, nullable=False)
+    payload_type_id = Column(Integer, ForeignKey('PayloadType.id'))
+
+    # Relationship to PayloadType
+    payload_type = relationship("PayloadType", back_populates="payload_iovs")
+```
+## Create Tables
+We create all the tables in the database.
+
+```python
+# Create all tables in the database
+Base.metadata.drop_all(engine)
+Base.metadata.create_all(engine)
+```
+## Adding Example Data
+We add some example data to the database for `GlobalTag`, `PayloadType`, and `PayloadIOV`.
+
+```python
+# Adding example data
+global_tag = GlobalTag(name="DetectorConfiguration")
+session.add(global_tag)
+
+daq_payload_type = PayloadType(name="DAQSettings", global_tag=global_tag)
+dcs_payload_type = PayloadType(name="DCSSettings", global_tag=global_tag)
+
+session.add(daq_payload_type)
+session.add(dcs_payload_type)
+
+daq_payload_iovs = [
+    PayloadIOV(payload_url="http://example.com/daq1", iov=1, payload_type=daq_payload_type),
+    PayloadIOV(payload_url="http://example.com/daq2", iov=2, payload_type=daq_payload_type),
+    PayloadIOV(payload_url="http://example.com/daq3", iov=3, payload_type=daq_payload_type)
+]
+
+dcs_payload_iovs = [
+    PayloadIOV(payload_url="http://example.com/dcs1", iov=1, payload_type=dcs_payload_type),
+    PayloadIOV(payload_url="http://example.com/dcs2", iov=2, payload_type=dcs_payload_type),
+    PayloadIOV(payload_url="http://example.com/dcs3", iov=3, payload_type=dcs_payload_type)
+]
+
+session.add_all(daq_payload_iovs)
+session.add_all(dcs_payload_iovs)
+session.commit()
+```
+## Query the Database
+Finally, we query the database to get the latest `PayloadIOV` entries for each `PayloadType` for a specific `GlobalTag` and IOV.
+
+```python
+# Query to get the last PayloadIOV entries for each PayloadType for a specific GlobalTag and IOV
+requested_iov = 2
+requested_gt = "DetectorConfiguration"
+
+# Subquery to find the maximum IOV for each PayloadType
+subquery = (session.query(
+                PayloadIOV.payload_type_id,
+                func.max(PayloadIOV.iov).label('max_iov')
+            )
+            .join(PayloadType, PayloadType.id == PayloadIOV.payload_type_id)
+            .join(GlobalTag, GlobalTag.id == PayloadType.global_tag_id)
+            .filter(GlobalTag.name == requested_gt, PayloadIOV.iov <= requested_iov)
+            .group_by(PayloadIOV.payload_type_id)
+            .subquery())
+
+# Main query to get the latest PayloadIOV for each PayloadType
+query = (session.query(
+            GlobalTag.name.label('global_tag_name'),
+            PayloadType.name.label('payload_type_name'),
+            PayloadIOV.payload_url,
+            subquery.c.max_iov
+         )
+         .join(PayloadType, GlobalTag.id == PayloadType.global_tag_id)
+         .join(subquery, subquery.c.payload_type_id == PayloadType.id)
+         .join(PayloadIOV, and_(
+             PayloadType.id == PayloadIOV.payload_type_id,
+             subquery.c.max_iov == PayloadIOV.iov
+         ))
+         .filter(GlobalTag.name == requested_gt)
+         .order_by(PayloadType.name)
+        ).all()
+
+for global_tag_name, payload_type_name, payload_url, max_iov in query:
+    print(f"GlobalTag: {global_tag_name}, PayloadType: {payload_type_name}, PayloadIOV URL: {payload_url}, IOV: {max_iov}")
+```
+
+    GlobalTag: DetectorConfiguration, PayloadType: DAQSettings, PayloadIOV URL: http://example.com/daq2, IOV: 2
+    GlobalTag: DetectorConfiguration, PayloadType: DCSSettings, PayloadIOV URL: http://example.com/dcs2, IOV: 2