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Migrate from legacy SQLAlchemy 1.x query patterns to modern 2.0 style for better performance, clarity, and future compatibility. This involves several key transformations:

Query Construction:

• Use select() instead of session.query()
• Use where() instead of filter()

Result Retrieval:

• Use session.scalar(stmt) instead of session.execute(stmt).scalars().first()
• Use session.scalars(stmt) instead of session.execute(stmt).scalars()
• Be careful with column-specific queries - they require session.execute(stmt) not session.scalars(stmt)

Example transformations:

# Legacy 1.x style
user = db.session.query(User).filter(User.id == user_id).first()
users = db.session.query(User).filter(User.active == True).all()

# Modern 2.0 style  
stmt = select(User).where(User.id == user_id)
user = db.session.scalar(stmt)

stmt = select(User).where(User.active.is_(True))
users = db.session.scalars(stmt).all()

# Column-specific queries (note: use execute, not scalars)
stmt = select(User.id, User.name).where(User.active.is_(True))
results = db.session.execute(stmt).all()

Boolean Comparisons: Use .is_(True) or .is_(False) instead of == True/False for explicit boolean comparisons.

This migration improves code maintainability, leverages SQLAlchemy’s latest optimizations, and ensures compatibility with future versions.