XPPL/app/models.py

from app import db
from marshmallow import Schema, fields, ValidationError, pre_load

class Book(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    title = db.Column(db.String(255))
    author = db.Column(db.String(255))
    file = db.Column(db.String(255))
    tag = db.Column(db.String(255))


    def __init__(self, title, author, file, tag):
        self.title = title
        self.author = author
        self.file = file
        self.tag = tag

    def __repr__(self):
        return '<Title %r>' % self.title


class BookSchema(Schema):
    id = fields.Int(dump_only=True)
    title = fields.Str()
    author = fields.Str()
    file = fields.Str()
    tag = fields.Str()

def must_not_be_blank(data):
    if not data:
        raise ValidationError('You forgot to write stuff.')