How to add UniqueConstraint in SQLAlchemy

Question

How does one add a UniqueConstraint which is Case Insensitive using SQLalchemy?

Answer 1

To add upon @jspcal's answer, if the model is defined using a class, then one you would have to either instantiate it independently after declaring the model or use the text construct.

i.e.

from sqlalchemy.sql.expressions import func

class User(Base):
    __tablename__ = 'user'
    username = Column('username', String(24), nullable=False)
    
Index('user_username_index', func.lower(User.username), unique=True)

using the text construct:

from sqlalchemy.sql.expressions import text

class User(Base):
    __tablename__ = 'user'
    __table_args__ = (
        Index('ix_user_name', text('LOWER(username)')), 
    )
    username = Column('username', String(24), nullable=False)
    

NB: table_args needs to be a tuple or dict, hence the need for that trailing comma inside the parenthesis.

That will create an index on username column of table user in lowercase form. Therefore, data stored in this column is unique and case insensitive.