Does Auto-truncation not work with mariadb? Or does it need to be manually turned on?

This issue is in continuation of #3989

Describe the bug

Exact error received is:

sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError) (1059, "Identifier name 'fk_faculty_marks_assistant_department_subject_id_department_subject' is too long")

Expected behavior

Sqlalchemy should auto-truncate the constraint name as it is above 64 characters.

I am expecting this behaviour as the original issue is marked as fixed and closed.

To Reproduce

I don’t know how to create a unit test for naming conventions and alembic. Any example link will be appreciated.

The Naming Convention used:

convention = {
    "ix": 'ix_%(column_0_N_label)s',
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(constraint_name)s",
    "fk": "fk_%(table_name)s_%(column_0_N_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s"
}

Relevant models:

class DepartmentSubject(db.Model):
    __tablename__ = 'department_subject'

    id = db.Column(db.SmallInteger, primary_key=True)


class FacultyMarksAssistant(db.Model):
    __tablename__ = 'faculty_marks_assistant'

    department_subject_id = db.Column(
        db.ForeignKey('department_subject.id'),
        primary_key=True, nullable=False, index=True
    )

Error

sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError) (1059, "Identifier name 'fk_faculty_marks_assistant_department_subject_id_department_subject' is too long")

Versions.

• OS: archlinux 5.9.14-arch1-1
• Python: 3.9.0
• SQLAlchemy: 1.3.20
• Database: mariadb Ver 15.1 Distrib 10.5.8-MariaDB, for Linux (x86_64) using readline 5.1
• DBAPI: mysqlclient 2.0.2

Additional context

the MySQL dialect has two separate lengths set up and these are likely not accommodated >correctly:

identifiers are 64, however aliases can be 255…

max_identifier_length = 255
max_index_name_length = 64

_Originally posted by @zzzeek in https://github.com/sqlalchemy/sqlalchemy/issues/3989#issuecomment-770219401_

Where would I find this and check?

[zzzeek]

latest rel_1_3 branch + master should work now if you feel like testing, thanks for reporting!

[zzzeek]

pretty weird that most MySQL versions are not even applying this foreign key name to the foreign key constraint itself; only MySQL 8 is doing it. mariadb versions are naming the FK with a generated name and using the name on a related KEY element only.