如何将Python对象转换为String？

Question

QuerySelectField is displaying the query correctly but its not saving in the database, it shows the following error while submitting.

ProgrammingError: (ProgrammingError) can't adapt type 'Category' 'INSERT INTO articles (title, body, category, created) VALUES (%(title)s, %(body)s, %(category)s, %(created)s) RETURNING articles.id' {'category': <blog.models.Category object at 0x03A7E2D0>, 'body': u'Test', 'title': u'This is the New Post', 'created': datetime.datetime(2013, 10, 16, 14, 7, 23, 508000)}

When i enter the title and content and choose the category which is displayed by quering the results from category database and when trying to submit, it throws the above error.

I know my the error is this line

{'category': <blog.models.Category object at 0x03A7E2D0>

How can i get it correct, where i am missing badly.

---

Forms.py

from models import DBSession
from models import Category
from wtforms import Form, TextField, TextAreaField, SubmitField, validators
from wtforms.ext.sqlalchemy.fields import QuerySelectField

def category_choice():
    return DBSession.query(Category)

class ArticleCreateForm(Form):
    title = TextField('Title', [validators.required(), validators.length(min=1,max=240)])
    body = TextAreaField('Content', [validators.required()])
    category = QuerySelectField('Category', query_factory=category_choice )
    submit = SubmitField()


class CategoryCreateForm(Form):
    name = TextField('Name', [validators.required(), validators.length(min=1,max=240)])
    description = TextAreaField('Description', [validators.required()])
    submit = SubmitField()

Views.py

@view_config(route_name='article_action', match_param='action=create', renderer='articles/create.jinja2')
def create(request):
    article = Article()
    category = Category()
    form = ArticleCreateForm(request.POST)
    if request.method == 'POST' and form.validate():
        form.populate_obj(article )
        DBSession.add(article, category)
        return HTTPFound(location=request.route_url('home'))
    return {'form':form, 'action':request.matchdict.get('create')}

Models.py

class Category(Base):
    __tablename__ = 'categories'
    id = Column(Integer, primary_key=True)
    name = Column(String(100), unique=True, nullable=False)
    description = Column(Text, nullable=False)

    def __unicode__(self):
        return self.name

class Article(Base):
    __tablename__ = 'articles'
    id = Column(Integer, primary_key=True)
    title = Column(String(255), unique=True, nullable=False)
    body =  Column(Text, nullable=False)
    category = Column(ForeignKey(Category.name), nullable=False)
    created = Column(DateTime, default=datetime.datetime.now)


    @property
    def slug(self):
        return urlify(self.title)

    @property
    def created_in_words(self):
        return time_ago_in_words(self.created)

Create.jinja2

{% extends 'base.jinja2' %}

{% block content %}
    <form action="{{ request.route_url('article_action', action='create') }}" method="post">
        {{ form.title.label }}
        {{ form.title }}<br/>

        {{ form.body.label }}
        {{ form.body }}<br/>

        {{ form.category.label }}
        {{ form.category }}<br/>

        {{ form.submit }}
    </form>
        <a href="{{ request.route_url('home') }}">Home</a>
{% endblock %}

Full Traceback

Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\pyramid_debugtoolbar\panels\performance.py", line 69, in noresource_timer_handler
    result = handler(request)
  File "C:\Python27\lib\site-packages\pyramid\tweens.py", line 21, in excview_tween
    response = handler(request)
  File "C:\Python27\lib\site-packages\pyramid_tm\__init__.py", line 82, in tm_tween
    reraise(*exc_info)
  File "C:\Python27\lib\site-packages\pyramid_tm\__init__.py", line 70, in tm_tween
    manager.commit()
  File "C:\Python27\lib\site-packages\transaction\_manager.py", line 111, in commit
    return self.get().commit()
  File "C:\Python27\lib\site-packages\transaction\_transaction.py", line 280, in commit
    reraise(t, v, tb)
  File "C:\Python27\lib\site-packages\transaction\_transaction.py", line 271, in commit
    self._commitResources()
  File "C:\Python27\lib\site-packages\transaction\_transaction.py", line 417, in _commitResources
    reraise(t, v, tb)
  File "C:\Python27\lib\site-packages\transaction\_transaction.py", line 389, in _commitResources
    rm.tpc_begin(self)
  File "C:\Python27\lib\site-packages\zope\sqlalchemy\datamanager.py", line 90, in tpc_begin
    self.session.flush()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1818, in flush
    self._flush(objects)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1936, in _flush
    transaction.rollback(_capture_exception=True)
  File "C:\Python27\lib\site-packages\sqlalchemy\util\langhelpers.py", line 58, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1900, in _flush
    flush_context.execute()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 372, in execute
    rec.execute(self)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 525, in execute
    uow
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\persistence.py", line 64, in save_obj
    table, insert)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\persistence.py", line 569, in _emit_insert_statements
    execute(statement, params)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 662, in execute
    params)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 761, in _execute_clauseelement
    compiled_sql, distilled_params
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 874, in _execute_context
    context)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 1024, in _handle_dbapi_exception
    exc_info
  File "C:\Python27\lib\site-packages\sqlalchemy\util\compat.py", line 195, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 867, in _execute_context
    context)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\default.py", line 324, in do_execute
    cursor.execute(statement, parameters)
ProgrammingError: (ProgrammingError) can't adapt type 'Category' 'INSERT INTO articles (title, body, category, created) VALUES (%(title)s, %(body)s, %(category)s, %(created)s) RETURNING articles.id' {'category': <blog.models.Category object at 0x03A7E2D0>, 'body': u'Test', 'title': u'This is the New Post', 'created': datetime.datetime(2013, 10, 16, 14, 7, 23, 508000)}

Answer 1

Your problem lies here:

form.populate_obj(article)

This basically assigns the form field values to the database object's corresponding fields. However, you are not using a SQLAlchemy relationship (you should!) so article.category needs to contain the name (why not ID?!) of the category. However, the QuerySelectField has the database object (ie a Category instance) as its value.

You have three options; the third one is the preferred one:

• Use a normal SelectField with choices populated from the database

• Don't use populate_obj but assign the category manually using

   article.category = form.category.data.name 

• Rename the category column in Article to eg category_name and use a relationship() so Article.category does not contain the name but a Category object.

Answer 2

The category relationship in your Article model is not correct. It has two problems:

1. you have not provided the data type for the column.
2. Article.category needs to be a relationship, not a column.

If you modify your Article class to something like this things should improve:

class Article(Base):
    ...
    category_name = Column(String(100), ForeignKey(Category.name), nullable=False)
    category = relationship(Category)

If you do that SQLAlchemy will know that the category property must be a Category instance and will automatically load and save Category instances as needed.

Answer 3

将关系添加到您的模型字段。