I keep getting this IntegrityError

from flask import (Flask, g, render_template, flash, redirect,
                  url_for)
from flask.ext.login import (LoginManager,login_user, logout_user,
                            login_required, current_user)
from flask.ext.bcrypt import check_password_hash

import models
import forms

DEBUG = True
PORT = 8000
HOST = '0.0.0.0'


app = Flask(__name__)
app.secret_key = 'wiedhwoijdowijedowijdejdwejdwaejd3948d93'

login_manager = LoginManager()
login_manager.init_app(app)
login_manager.login_view = 'login'


@login_manager.user_loader
def load_user(userid):
  try:
    return models.User.get(models.User.id == userid)
  except models.DoesNotExist:
    return None


@app.before_request
def before_request():
  """Connect to db before each request"""
  g.db = models.DATABASE
  g.db.connect()
  g.user = current_user


@app.after_request
def after_request(response):
  """Close db connection after each request"""
  g.db.close()
  return response

@app.route('/register', methods=('GET', 'POST'))
def register():
    form = forms.RegisterForm()
    if form.validate_on_submit():
        flash("Yay, you registered!", "success")
        models.User.create_user(
            username=form.username.data,
            email=form.email.data,
            password=form.password.data
        )
        return redirect(url_for('index'))
    return render_template('register.html', form=form)


@app.route('/login', methods=('GET', 'POST'))
def login():
    form = forms.LoginForm()
    if form.validate_on_submit():
        try:
            user = models.User.get(models.User.email == form.email.data)
        except models.DoesNotExist:
            flash("Your email or password doesn't match!", "error")
        else:
            if check_password_hash(user.password, form.password.data):
                login_user(user)
                flash("You've been logged in!", "success")
                return redirect(url_for('index'))
            else:
                flash("Your email or password doesn't match!", "error")
    return render_template('login.html', form=form)



@app.route('/logout')
@login_required
def logout():
  logout_user()
  flash('You have been logged out', "success")
  return redirect(url_for('index'))



@app.route('/')
def index():
  return render_template('index1.html')

@app.route('/create-taco', methods=('GET','POST'))
@login_required
def create_taco():
  form = forms.CreateTacoForm()
  if form.validate_on_submit():
    models.Taco.create(user=g.user._get_current_object(),
                       extras=form.extras.data.strip())
    flash('Taco created!', "success")
    return redirect(url_form('index'))
  return render_template('taco.html', form=form)



if __name__ == '__main__':
  models.initialize()
  try:
    models.User.create_user(
      username='nadav',
      email='nadav@reis.com',
      password='password',
      admin=True
    )
  except ValueError:
    pass
  app.run(debug=DEBUG, host=HOST, port=PORT)

import datetime

from flask.ext.bcrypt import generate_password_hash
from flask.ext.login import UserMixin
from peewee import *

DATABASE = SqliteDatabase('tacocat.db')

class User(UserMixin, Model):
    username = CharField(unique=True)
    email = CharField(unique=True)
    password = CharField(max_length=100)
    joined_at = DateTimeField(default=datetime.datetime.now)
    is_admin = BooleanField(default=False)

    class Meta:
        database = DATABASE
        order_by = ('-joined_at',)

    def get_posts(self):
        return Post.select().where(Post.user == self)

    def get_stream(self):
        return Post.select().where(
            (Post.user == self)
        )

    #def following(self):
     #   """The users that we are following."""
      #  return (
       #     User.select().join(
        #        Relationship, on=Relationship.to_user
         #   ).where(
          #      Relationship.from_user == self
          # )
        # )

#    def followers(self):
#        """Get users following the current user"""
#        return (
#            User.select().join(
#                Relationship, on=Relationship.from_user
#            ).where(
#                Relationship.to_user == self
#            )
#        )

    @classmethod
    def create_user(cls, username, email, password, admin=False):
        try:
            with DATABASE.transaction():
                cls.create(
                    username=username,
                    email=email,
                    password=generate_password_hash(password),
                    is_admin=admin)
        except IntegrityError:
            raise ValueError("User already exists")


class Taco(Model):
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(
        rel_model=User,
        related_name='tacos'
    )
    protein = CharField()
    cheese = CharField()
    shell = CharField()
    extras = CharField()




    class Meta:
        database = DATABASE
        order_by = ('-timestamp',)


#class Relationship(Model):
#    from_user = ForeignKeyField(User, related_name='relationships')
#    to_user = ForeignKeyField(User, related_name='related_to')

    class Meta:
        database = DATABASE
#        indexes = (
#            (('from_user', 'to_user'), True)
#        )


def initialize():
    DATABASE.connect()
    DATABASE.create_tables([User, Taco], safe=True)
    DATABASE.close()

from flask_wtf import Form
from wtforms import StringField, PasswordField, TextAreaField, BooleanField
from wtforms.validators import (DataRequired, Regexp, ValidationError, Email,
                               Length, EqualTo)

from models import User


def name_exists(form, field):
    if User.select().where(User.username == field.data).exists():
        raise ValidationError('User with that name already exists.')


def email_exists(form, field):
    if User.select().where(User.email == field.data).exists():
        raise ValidationError('User with that email already exists.')


class RegisterForm(Form):
    username = StringField(
        'Username',
        validators=[
            DataRequired(),
            Regexp(
                r'^[a-zA-Z0-9_]+$',
                message=("Username should be one word, letters, "
                         "numbers, and underscores only.")
            ),
            name_exists
        ])
    email = StringField(
        'Email',
        validators=[
            DataRequired(),
            Email(),
            email_exists
        ])
    password = PasswordField(
        'Password',
        validators=[
            DataRequired(),
            Length(min=2),
            EqualTo('password2', message='Passwords must match')
        ])
    password2 = PasswordField(
        'Confirm Password',
        validators=[DataRequired()]
    )


class LoginForm(Form):
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])


class CreateTacoForm(Form):
    #content = TextAreaField("What's up?", validators=[DataRequired()])
    protein = StringField(
        "Protein",
        validators=[
          DataRequired()
        ])
    cheese = StringField(
        "Cheese",
        validators=[
          DataRequired()
        ])
    shell = StringField(
        "Shell",
        validators=[
          DataRequired()
        ])
    extras=TextAreaField("Extras")