sqlalchemy FetchedValue 和 primary_key

Question

我正在尝试创建一个使用 UUID_SHORT() 作为主键的表。我有一个触发器，可以在您进行插入时插入一个值。我无法让 sqlalchemy 将列识别为 primary_key 而不抱怨不提供默认值。如果我确实包含了一个默认值，即使在刷新之后它也会使用该默认值，尽管声明了server_default=FetchedValue()。我似乎可以让事情正常工作的唯一方法是列不是主键。

我正在使用 Pyramid、SQLAlchemy ORM 和 MySQL。

这是模型对象：

Base = declarative_base()
class Patient(Base):
    __tablename__ = 'patient'
    patient_id = Column(BigInteger(unsigned=True), server_default=FetchedValue(), primary_key=True, autoincrement=False)
    details = Column(Binary(10000))

在 initializedb.py 我有：

with transaction.manager:
    patient1 = Patient(details = None)
    DBSession.add(patient1)
    DBSession.flush()
    print(patient1.patient_id)

运行 ../bin/initialize_mainserver_db development.ini 给我以下错误：

2012-11-01 20:17:22,168 INFO  [sqlalchemy.engine.base.Engine][MainThread] BEGIN (implicit)
2012-11-01 20:17:22,169 INFO  [sqlalchemy.engine.base.Engine][MainThread] INSERT INTO patient (details) VALUES (%(details)s)
2012-11-01 20:17:22,169 INFO  [sqlalchemy.engine.base.Engine][MainThread] {'details': None}
2012-11-01 20:17:22,170 INFO  [sqlalchemy.engine.base.Engine][MainThread] ROLLBACK
Traceback (most recent call last):
  File "/sites/metrics_dev/lib/python3.3/site-packages/sqlalchemy/engine/base.py", line 1691, in _execute_context
    context)
  File "/sites/metrics_dev/lib/python3.3/site-packages/sqlalchemy/engine/default.py", line 333, in do_execute
    cursor.execute(statement, parameters)
  File "/sites/metrics_dev/lib/python3.3/site-packages/mysql/connector/cursor.py", line 418, in execute
    self._handle_result(self._connection.cmd_query(stmt))
  File "/sites/metrics_dev/lib/python3.3/site-packages/mysql/connector/cursor.py", line 345, in _handle_result
    self._handle_noresultset(result)
  File "/sites/metrics_dev/lib/python3.3/site-packages/mysql/connector/cursor.py", line 321, in _handle_noresultset
    self._warnings = self._fetch_warnings()
  File "/sites/metrics_dev/lib/python3.3/site-packages/mysql/connector/cursor.py", line 608, in _fetch_warnings
    raise errors.get_mysql_exception(res[0][1],res[0][2])
mysql.connector.errors.DatabaseError: 1364: Field 'patient_id' doesn't have a default value

使用 mysql 客户端运行手动插入会导致一切正常，因此问题似乎出在 SQLAlchemy 上。

mysql> insert into patient(details) values (null);
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select * from patient;
+-------------------+---------+
| patient_id        | details |
+-------------------+---------+
| 94732327996882980 | NULL    |
+-------------------+---------+
1 row in set (0.00 sec)

mysql> show triggers;
+-----------------------+--------+---------+-------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| Trigger               | Event  | Table   | Statement                           | Timing | Created | sql_mode | Definer        | character_set_client | collation_connection | Database Collation |
+-----------------------+--------+---------+-------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
| before_insert_patient | INSERT | patient | SET new.`patient_id` = UUID_SHORT() | BEFORE | NULL    |          | root@localhost | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
+-----------------------+--------+---------+-------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)

Answer 1

这是我作为解决方法所做的...

DBSession.execute(
"""CREATE TRIGGER before_insert_patient BEFORE INSERT ON `patient`
    FOR EACH ROW BEGIN
        IF (NEW.patient_id IS NULL OR NEW.patient_id = 0) THEN
            SET NEW.patient_id = UUID_SHORT();
        END IF;
    END""")

在患者类中：

patient_id = Column(BigInteger(unsigned=True), default=text("uuid_short()"), primary_key=True, autoincrement=False, server_default="0")

因此，只有当有人直接访问数据库而不是通过 python 代码访问数据库时，触发器才会执行某些操作。并且希望没有人这样做 patient1 = Patient(patient_id=0, details = None) 因为 SQLAlchemy 将使用“0”值而不是触发器产生的值

Answer 2

为了完整起见，根据您的回答，这里有另外两种可能的解决方案（也可以使用here）。它们比您的解决方案稍微简单一些（省略传递具有正确默认值的参数）并使用 SQLAlchemy 构造来定义触发器。

#!/usr/bin/env python3

from sqlalchemy import BigInteger, Column, create_engine, DDL, event
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.schema import FetchedValue
from sqlalchemy.sql.expression import func

Base = declarative_base()

class PatientOutputMixin(object):
    '''
    Mixin to output human readable representations of models.
    '''
    def __str__(self):
        return '{}'.format(self.patient_id)

    def __repr__(self):
        return str(self)


class Patient1(Base, PatientOutputMixin):
    '''
    First version of ``Patient`` model.
    '''
    __tablename__ = 'patient_1'

    patient_id = Column(BigInteger, primary_key=True,
                        default=func.uuid_short())

# the following trigger is only required if columns are inserted in the table
# not using the above model/table definition, otherwise it is redundant
create_before_insert_trigger = DDL('''
CREATE TRIGGER before_insert_%(table)s BEFORE INSERT ON %(table)s
FOR EACH ROW BEGIN
    IF NEW.patient_id IS NULL THEN
        SET NEW.patient_id = UUID_SHORT();
    END IF;
END
''')

event.listen(Patient1.__table__, 'after_create',
             create_before_insert_trigger.execute_if(dialect='mysql'))
# end of optional trigger definition


class Patient2(Base, PatientOutputMixin):
    '''
    Second version of ``Patient`` model.
    '''
    __tablename__ = 'patient_2'

    patient_id = Column(BigInteger, primary_key=True,
                        default=0, server_default=FetchedValue())

create_before_insert_trigger = DDL('''
CREATE TRIGGER before_insert_%(table)s BEFORE INSERT ON %(table)s
FOR EACH ROW BEGIN
    SET NEW.patient_id = UUID_SHORT();
END
''')

event.listen(Patient2.__table__, 'after_create',
             create_before_insert_trigger.execute_if(dialect='mysql'))


# test models

engine = create_engine('mysql+oursql://test:test@localhost/test?charset=utf8')

Base.metadata.bind = engine
Base.metadata.drop_all()
Base.metadata.create_all()

Session = sessionmaker(bind=engine)

session = Session()

for patient_model in [Patient1, Patient2]:
    session.add(patient_model())
    session.add(patient_model())
    session.commit()

    print('{} instances: {}'.format(patient_model.__name__,
                                    session.query(patient_model).all()))

运行上述脚本会产生以下（示例）输出：

Patient1 instances: [22681783426351145, 22681783426351146]
Patient2 instances: [22681783426351147, 22681783426351148]