how to use QuerySelectField in flask?

Question

I am trying to have a select field filled with the results of a sqlalchemy request in a flask form.

Here are the code :

def possible_book():
    return Book.query.with_entities(Book.id).all()

class AuthorForm(Form):
    familyname  = TextField('familyname', [validators.Required()])
    firstname   = TextField('firstname', [validators.Required()])
    book_list = QuerySelectField('book_list',query_factory=possible_book,get_label='title',allow_blank=True)

This is the template :

 <form action="" method="post" name="edit_author" enctype="multipart/form-data">
     {{form.hidden_tag()}}
    <p>Veuillez donner son prénom (obligatoire) :    {{form.firstname(value=author.firstname)}}</p>
    <p>Nom de famille (obligatoire) : {{form.familyname(value=author.familyname)}}</p>
    <p>Livre : {{form.book_list}}</p>

    <p><input type="submit" value="Envoyer"></p>
 </form>

View :

@app.route('/edit_author/<number>', methods = ['GET', 'POST'])
   def edit_author(number):
   if number == 'new':
      author = []
   else:
      author = Author.query.filter_by(id = number).first()
   form = AuthorForm()
   if form.validate_on_submit():
      a = Author(firstname= form.firstname.data, familyname= form.familyname.data)
      a.books = form.book_list.data

       db.session.add(a)
       db.session.commit()
   return redirect('/admin')
return render_template('edit_author.html', form = form, author = author)

The model (pasted only the associative table and the author table, much of the column are out of the question)

author_book = db.Table('author_book',
    db.Column('author', db.Integer, db.ForeignKey('author.id')),
    db.Column('book', db.Integer, db.ForeignKey('book.id'))
)

class Author(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    firstname = db.Column(db.String(64), index = True)
    familyname = db.Column(db.String(120), index = True)
    website = db.Column(db.String(120))
    dateofbirth = db.Column(db.DateTime)
    placeofbirth = db.Column(db.String(120))
    nationality = db.Column(db.String(120))
    biography = db.Column(db.Text)
    photo = db.Column(db.String(120))
    books = db.relationship('Book', secondary=author_book,backref=db.backref('author', lazy='dynamic'))

I currently get this error :

UnmappedInstanceError: Class 'sqlalchemy.util._collections.KeyedTuple' is not mapped

What I really want is that the select field show the author name and his number, and return the author number to the app (to the function called "add_author" on the head).

Thank you.

Answer 1

You have two problems:

1. As Sean Vieira pointed out in his answer, the query_factory callback should return a query, not the results.

2. The query_factory callback should return complete entities, in your case books, not book ids. I believe the QuerySelectField must be trying to use the results of the query as if they are mapped objects but the ids (returned as KeyedTuple instances) are not.

I think this is the correct way to code the callback function:

def possible_book():
    return Book.query

Answer 2

One possible problem is that wtforms.ext.sqlalchemy.fields.QuerySelectField expects a SQLAlchemy query object, not a materialized list. Simply remove the all() call from your possible_book return to return an unmaterialized query to WTForms:

def possible_book():
    return Book.query.with_entities(Book.id)