sqlalchemy unique across multiple columns

Extract from the documentation of the Column:

unique – When True, indicates that this column contains a unique constraint, or if index is True as well, indicates that the Index should be created with the unique flag. To specify multiple columns in the constraint/index or to specify an explicit name, use the UniqueConstraint or Index constructs explicitly.

As these belong to a Table and not to a mapped Class, one declares those in the table definition, or if using declarative as in the __table_args__:

# version1: table definitionmytable = Table('mytable', meta,    # ...    Column('customer_id', Integer, ForeignKey('customers.customer_id')),    Column('location_code', Unicode(10)),    UniqueConstraint('customer_id', 'location_code', name='uix_1')    )# or the index, which will ensure uniqueness as wellIndex('myindex', mytable.c.customer_id, mytable.c.location_code, unique=True)# version2: declarativeclass Location(Base):    __tablename__ = 'locations'    id = Column(Integer, primary_key = True)    customer_id = Column(Integer, ForeignKey('customers.customer_id'), nullable=False)    location_code = Column(Unicode(10), nullable=False)    __table_args__ = (UniqueConstraint('customer_id', 'location_code', name='_customer_location_uc'),                     )

from flask_sqlalchemy import SQLAlchemydb = SQLAlchemy()class Location(Base):      __table_args__ = (        # this can be db.PrimaryKeyConstraint if you want it to be a primary key        db.UniqueConstraint('customer_id', 'location_code'),      )      customer_id = Column(Integer,ForeignKey('customers.customer_id')      location_code = Column(Unicode(10))