Question

I am trying to populate a dropdown in Flask via SQLAlchemy calling on an oracle database. The table in the Database has one column 'VALUE' and the values make up the drop down list. I am running into the error: ValueError: need more than 1 value to unpack

Any ideas on what is missing here?

engine = create_engine('oracle+cx_oracle://user:pass@DB.name/')
connection = engine.connect()
Base= declarative_base()

GP_DD_UPDATE_FREQ = Table('GP_DD_UPDATE_FREQ', Base.metadata,
                    Column('VALUE', String(20)))

class Dropdown():
    s = select([GP_DD_UPDATE_FREQ.c.VALUE])
    result = connection.execute(s)
    ape = [row for row in result ]

updatef = Updatefreq.ape

class ReusableForm(Form):  
    updates = SelectField('Update:', coerce=int, choices = updatef)

@app.route("/editor", methods=['GET', 'POST'])
def hello():
    form = ReusableForm(request.form)  # calls on form

    if request.method == 'POST':
        updates = request.form['updates']

hello.html

<label for="updates">Update Frequency {{ form.updates}}</label>

Also the list of values populates just fine if I print updatef

Answer 1

我认为这个错误是由于您对SQLAlchemy查询结果的错误处理造成的。在班级Dropdown

class Dropdown():
    s = select([GP_DD_UPDATE_FREQ.c.VALUE])
    result = connection.execute(s)
    ape = [row for row in result ]

result是执行SQLALchemy查询。它是一个ResultProxy对象。这个ResultProxy对象是可迭代的，迭代时的每个元素都是元组。即使您的SELECT查询仅提取表的一列，但每个返回的行都表示为tuple而不是scalar！

例如，假设您的表格列VALUE是这样的：

VALUE
-------
1
2
3

查询的返回结果表示为：

(1,)
(2,)
(3,)

您可能会注意到ResultProxy类提供了许多操作功能，例如

fetchall(), return [(1,), (2,), (3,)], a list of tuple
fetchone(), return (1,), a tuple (first time call)
fetchmany(2), return [(1,), (2,)], a list of tuple
first(), return (1,), a tuple
scalar(), return 1, a scalar

在您的应用程序中，您需要一个标量列表，而不是

ape = [row for row in result]

你应该使用

ape = [row[0] for row in result]

或者

ape = [first_of_row for first_of_row, in result]

希望这个插图可以回答。谢谢！

SQLAlchemy/Flask Populating a Dropdown list error

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