更新模型后，烧瓶SQLAlchemy升级失败。需要有关我的修复工作原理的解释

我跟着一本书尝试创建Flask博客。我是Flask的新手。我更新了一个模型，因此代码如下所示：

class Entry(db.Model):
    STATUS_PUBLIC = 0
    STATUS_DRAFT = 1
    STATUS_DELETED = 2

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100))
    slug = db.Column(db.String(100), unique=True)
    body = db.Column(db.Text)
    status = db.Column(db.SmallInteger, default=STATUS_PUBLIC)
    created_timestamp = db.Column(db.DateTime, default=datetime.datetime.now)
    modified_timestamp = db.Column(
        db.DateTime,
        default=datetime.datetime.now,
        Onupdate=datetime.datetime.now)
    author_id = db.Column(db.Integer, db.ForeignKey("user.id"))

添加最后一行author_id = db.Column(db.Integer, db.ForeignKey("user.id"))会导致数据库升级失败，并显示以下错误：

  File "manage.py", line 5, in 
    manager.run()
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/flask_script/__init__.py", line 412, in run
    result = self.handle(sys.argv[0], sys.argv[1:])
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/flask_script/__init__.py", line 383, in handle
    res = handle(*args, **config)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/flask_script/commands.py", line 216, in __call__
    return self.run(*args, **kwargs)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/flask_migrate/__init__.py", line 259, in upgrade
    command.upgrade(config, revision, sql=sql, tag=tag)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/command.py", line 254, in upgrade
    script.run_env()
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/script/base.py", line 425, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/util/pyfiles.py", line 93, in load_python_file
    module = load_module_py(module_id, path)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/util/compat.py", line 75, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "migrations/env.py", line 87, in 
    run_migrations_online()
  File "migrations/env.py", line 80, in run_migrations_online
    context.run_migrations()
  File "", line 8, in run_migrations
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/runtime/environment.py", line 836, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/runtime/migration.py", line 330, in run_migrations
    step.migration_fn(**kw)
  File "/home/devblog/projects/blog/app/migrations/versions/6b49bdaf06ce_.py", line 22, in upgrade
    batch_op.create_foreign_key(None, 'user', ['author_id'], ['id'])
  File "/usr/lib64/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/operations/base.py", line 299, in batch_alter_table
    impl.flush()
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/operations/batch.py", line 80, in flush
    fn(*arg, **kw)
  File "/home/devblog/projects/blog/venv/lib/python2.7/site-packages/alembic/operations/batch.py", line 337, in add_constraint
    raise ValueError("Constraint must have a name")
ValueError: Constraint must have a name

问题似乎与迁移脚本的升级功能有关：

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    with op.batch_alter_table('entry', schema=None) as batch_op:
        #batch_op.create_foreign_key(None, 'user', ['author_id'], ['id'])
        batch_op.create_foreign_key("author_id", 'user', ['author_id'], ['id'])

我通过注释掉原始行，删除None并使用来“修复”此问题'author_id'。

我使用了http://alembic.zzzcomputing.com/en/latest/ops.html上的文档来提出修复程序。相关部分：

create_foreign_key（约束名称，source_table，referent_table，local_cols，remote_cols，Onupdate= None，Ondelete= None，deferrable = None，初始= None，match = None，source_schema = None，referent_schema = None，** dialect_kw）

这将在内部生成一个包含必要列的Table对象，然后生成一个新的ForeignKeyConstraint对象，然后将其与Table关联。与该操作关联的任何事件侦听器都将正常触发。AddConstraint构造最终用于生成ALTER语句。

参数：name-外键约束的名称。该名称是必需的，以便可以发出ALTER语句。对于使用自动命名方案的设置（例如在配置约束命名约定中描述的设置），此处的名称可以为None，因为事件侦听器在将约束名称与表关联时会将其应用于约束对象。source_table –源表的字符串名称。referent_table –目标表的字符串名称。local_cols –源表中字符串列名称的列表。remote_cols –远程表中的字符串列名称的列表。onupdate –可选字符串。如果设置，则在为此约束发布DDL时发出ON UPDATE。典型值包括CASCADE，DELETE和RESTRICT。ondelete –可选字符串。如果设置，则在为此约束发布DDL时发出ON DELETE。典型值包括CASCADE，DELETE和RESTRICT。可延期–可选布尔。如果设置，则在为此约束发出DDL时发出DEFERRABLE或NOT DEFERRABLE。source_schema –源表的可选架构名称。referent_schema¶–目标表的可选架构名称。

我认为我添加了一个约束名称而不是None，从而“解决了”问题。它是否正确？

同样，该函数似乎需要5个自变量。仅用4个怎么工作？

任何建议表示感谢。

对于添加一个简单的外键列的情况，Mark Steward的解决方案对我来说非常理想。

无论您在哪里声明/定义“ db”，请执行以下操作-

from sqlalchemy import MetaData

naming_cOnvention= {
    "ix": 'ix_%(column_0_label)s',
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(column_0_name)s",
    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s"
}
db = SQLAlchemy(metadata=MetaData(naming_cOnvention=naming_convention))

然后，在您初始化迁移应用程序（烧瓶迁移）的地方，传递render_as_batch=True-

migrate.init_app(app, db, render_as_batch=True)