Case Insensitive Flask-SQLAlchemy Query

I’m using Flask-SQLAlchemy to query from a database of users; however, while

user = models.User.query.filter_by(username="ganye").first()

will return

<User u'ganye'>

doing

user = models.User.query.filter_by(username="GANYE").first()

returns

None

I’m wondering if there’s a way to query the database in a case insensitive way, so that the second example will still return

<User u'ganye'>

Answers:

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Method 1

You can do it by using either the lower or upper functions in your filter:

from sqlalchemy import func
user = models.User.query.filter(func.lower(User.username) == func.lower("GaNyE")).first()

Another option is to do searching using ilike instead of like:

.query.filter(Model.column.ilike("ganye"))

Method 2

Improving on @plaes’s answer, this one will make the query shorter if you specify just the column(s) you need:

user = models.User.query.with_entities(models.User.username).
filter(models.User.username.ilike("%ganye%")).all()

The above example is very useful in case one needs to use Flask’s jsonify for AJAX purposes and then in your javascript access it using data.result:

from flask import jsonify
jsonify(result=user)

Method 3

you can do

user = db.session.query(User).filter_by(func.lower(User.username)==func.lower("GANYE")).first()

Or you can use ilike function

 user = db.session.query(User).filter_by(User.username.ilike("%ganye%")).first()

Method 4

If it fits your use case, you may consider setting a custom collation on the column, such that the column automatically handles comparisons in a case-insensitive manner.

It’s worth noting:

• the collation will apply to all queries on the column
• the collation will apply to ORDER BY clauses as well
• a collation may be specified directly in queries, rather than being defined on the column
  • this may potentially incur performance penalties
• collation definitions tend to be RDBMS / locale / language-specific – consult the relevant documentation
• collation names may not be portable between different RDBMS
• available collation attributes may vary by RDBMS

in other words, consult your RDBMS’s docs before using this feature.

This example script shows how you might use collations for MySQL, Postgresql (note the special-casing) and Sqlite; each RDBMS returns all three possible results for the query value.

import sqlalchemy as sa
from sqlalchemy import orm

data = {
    'mysql': ('mysql:///test', 'utf8mb4_general_ci'),
    'postgresql': ('postgresql:///test', 'coll'),
    'sqlite': ('sqlite://', 'NOCASE'),
}


for dialect, (uri, collation) in data.items():
    Base = orm.declarative_base()

    class Test(Base):
        __tablename__ = 't16573095'

        id = sa.Column(sa.Integer, primary_key=True)
        name = sa.Column(sa.String(32, collation=collation))

    engine = sa.create_engine(uri, echo=False, future=True)
    Base.metadata.drop_all(engine)

    if dialect == 'postgresql':
        # Postgres collations are more complicated
        # - read the docs!
        with engine.begin() as conn:
            conn.execute(sa.text('DROP COLLATION IF EXISTS coll'))
            stmt = """CREATE COLLATION coll (provider='icu', locale='und-u-ks-level2', deterministic=false)"""
            conn.execute(sa.text(stmt))

    Base.metadata.create_all(engine)
    Session = orm.sessionmaker(engine, future=True)

    with Session.begin() as s:
        instances = [Test(name=name) for name in ['GANYE', 'ganye', 'gAnYe']]
        s.add_all(instances)

    with Session() as s:
        results = s.execute(sa.select(Test.name).where(Test.name == 'GaNyE')).scalars()
        print(f'{dialect:-<12}')
        for name in results:
            print(name)
        print('-' * 12)

To specify a collation in a query, use an attribute’s collate method:

with Session() as s:
    query = sa.select(Test).where(Test.name.collate('coll') == 'GaNyE')
    results = s.execute(query)

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0