Python/SQLAlchemy遷移 - ValueError：需要超過3個值才能在遷移時解壓

Question

我遵循Miguel Grinberg的優秀Flask Mega-Tutorial並使用他的數據庫創建和遷移腳本（找到here），但我遇到了問題當更改我的某個模型中的列時。

舊的模式是：

class Classes(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    day = db.Column(db.String(10)) 
    slot = db.Column(db.Integer) 
    enrolments = db.relationship('Enrolment', backref='class_slot', lazy='dynamic') 

    def __repr__(self): 
     return '<Classes - %r slot %d>' % (self.day, self.slot) 

class Enrolment(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    class_id = db.Column(db.Integer, db.ForeignKey('classes.id')) 
    studentnum = db.Column(db.String(10), index=True, unique=True) 
    name = db.Column(db.String(30)) 
    flags = db.Column(db.String(100)) 
    notes = db.Column(db.String(200)) 

    def __repr__(self): 
     return '<Enrolment - (%r) %r>' % (self.name, self.studentnum) 

與classes.day作爲一個字符串表示。不過，我想使之成爲一個外鍵關係這讓我可以輕鬆地搜索和排序的一天，所以我下面的代碼添加到模型：

class Days(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    day_name = db.Column(db.String(20), unique=True) 
    classes = db.relationship('Classes', backref='dayofweek', lazy='select') 

    def __repr__(self): 
     return '<Day - %r>' % self.day_name 

，然後修改類的模式，改變了天列：

day = db.Column(db.Integer, db.ForeignKey('days.id')) 

當運行遷移腳本，它與下面的錯誤產生模型時扼流圈：

aaron$ ./db_migrate.py 
Traceback (most recent call last): 
    File "./db_migrate.py", line 12, in <module> 
    script = api.make_update_script_for_model(SQLALCHEMY_DATABASE_URI, SQLALCHEMY_MIGRATE_REPO, tmp_module.meta, db.metadata) 
    File "<string>", line 2, in make_update_script_for_model 
    File "/Users/aaron/Dropbox/Development/put-attendance/flask/lib/python2.7/site-packages/migrate/versioning/util/__init__.py", line 90, in catch_known_errors 
    return f(*a, **kw) 
    File "<string>", line 2, in make_update_script_for_model 
    File "/Users/aaron/Dropbox/Development/put-attendance/flask/lib/python2.7/site-packages/migrate/versioning/util/__init__.py", line 160, in with_engine 
    return f(*a, **kw) 
    File "/Users/aaron/Dropbox/Development/put-attendance/flask/lib/python2.7/site-packages/migrate/versioning/api.py", line 321, in make_update_script_for_model 
    engine, oldmodel, model, repository, **opts) 
    File "/Users/aaron/Dropbox/Development/put-attendance/flask/lib/python2.7/site-packages/migrate/versioning/script/py.py", line 70, in make_update_script_for_model 
    genmodel.ModelGenerator(diff,engine).genB2AMigration() 
    File "/Users/aaron/Dropbox/Development/put-attendance/flask/lib/python2.7/site-packages/migrate/versioning/genmodel.py", line 223, in genB2AMigration 
    for modelCol, databaseCol, modelDecl, databaseDecl in td.columns_different: 
ValueError: need more than 3 values to unpack 

檢查td.columns_different表明，它只在列表中有一個項目 - 字符串'day'。

爲什麼它窒息，因爲我改變了數據庫中的字段類型？

Answer 1

是的，td.columns_different是在先前版本和當前版本之間更改的列的字典。此代碼屬於sqlalchemy-migrate軟件包。從源

評論[1]：

class TableDiff(object): 
    """ 
    ... 

    ..attribute:: columns_different 

    A dictionary containing information about columns that were 
    found to be different. 
    It maps column names to a :class:`ColDiff` objects describing the 
    differences found. 

對於溶液從字符串遷移您列類型爲Integer看到：How to alter column type from character varying to integer using sqlalchemy-migrate

[1] https://github.com/stackforge/sqlalchemy-migrate/blob/75034abe515a49e0efafb91519cfdf448ba02c73/migrate/versioning/schemadiff.py#L121