Fixed #15782 -- Prevented MySQL backend to crash on runserver when db server...

          characters if they have a unique index on them.

        """

        from django.db import models

        from MySQLdb import OperationalError

        try:

            db_version = self.connection.get_server_version()

            text_version = '.'.join([str(n) for n in db_version[:3]])

        except OperationalError:

            db_version = None

            text_version = ''

        varchar_fields = (models.CharField, models.CommaSeparatedIntegerField,

                models.SlugField)

        if isinstance(f, varchar_fields) and f.max_length > 255:

            if db_version < (5, 0, 3):

            if db_version and db_version < (5, 0, 3):

                msg = '"%(name)s": %(cls)s cannot have a "max_length" greater than 255 when you are using a version of MySQL prior to 5.0.3 (you are using %(version)s).'

            elif f.unique == True:

                msg = '"%(name)s": %(cls)s cannot have a "max_length" greater than 255 when using "unique=True".'

                msg = None

            if msg:

                errors.add(opts, msg % {'name': f.name, 'cls': f.__class__.__name__, 'version': '.'.join([str(n) for n in db_version[:3]])})

                errors.add(opts, msg % {'name': f.name, 'cls': f.__class__.__name__, 'version': text_version})