Case-insensitive exact match with SQLAlchemy - database

Question

How can I ensure that the = operator is always rendered case-insensitive? Are comparisions with the LOWER or the UPPER functions the best bet for performance? ILIKE seems to be very slow.

Answer 1

If you need only case-insensitivity use upper or lower since like is not only about case-insensitivity
example of lower:
my_string = 'BarFoo'
session.query(Foo).filter(func.lower(Foo.bar) == my_string.lower()).all()
see some more info on like here how to execute LIKE query in sqlalchemy?

Answer 2

For case-insensitive comparisons, you can subclass Comparator.
Building Custom Comparators
The example class below allows case-insensitive comparisons on the attribute named word_insensitive:
from sqlalchemy.ext.hybrid import Comparator, hybrid_property
from sqlalchemy import func, Column, Integer, String
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class CaseInsensitiveComparator(Comparator):
def __eq__(self, other):
return func.lower(self.__clause_element__()) == func.lower(other)
class SearchWord(Base):
__tablename__ = 'searchword'
id = Column(Integer, primary_key=True)
word = Column(String(255), nullable=False)
#hybrid_property
def word_insensitive(self):
return self.word.lower()
#word_insensitive.comparator
def word_insensitive(cls):
return CaseInsensitiveComparator(cls.word)
Above, SQL expressions against word_insensitive will apply the LOWER() SQL function to both sides:
>>> print Session().query(SearchWord).filter_by(word_insensitive="Trucks")
SELECT searchword.id AS searchword_id, searchword.word AS searchword_word FROM searchword
WHERE lower(searchword.word) = lower(:lower_1)
The CaseInsensitiveComparator above implements part of the ColumnOperators interface. A “coercion” operation like lowercasing can be applied to all comparison operations (i.e. eq, lt, gt, etc.) using Operators.operate():
class CaseInsensitiveComparator(Comparator):
def operate(self, op, other):
return op(func.lower(self.__clause_element__()), func.lower(other))