You might encounter this problem as I have when I was moving away from using Windows as my main Operating System, looking to install a linux based distribution. The issue with having dynamic disks is that the the new OS system you want to install will not recognise them, and you cannot proceed with the install or resize them or anything.

WARNING: Following this guide will result in deleting all of the data on your hard drive. Make sure that your data is backed up before proceeding.

What do you need

If your use case is the same as mine, moving from Windows to another OS it's best that you have 2 USB pen drives ready, but don't fret if you just have one USB drive it will just make the process longer. So basically what you need is:

• USB drive having a boot-able Windows 10 ISO burned to it. You can use Windows 7 for this too if you are still using it.
• USB drive having the OS you want to install (if this is in fact what you are doing)
• Some patience :)

Steps:

1. More important than anything, backup your data!
2. Having the Windows USB drive plugged in restart your machine into boot mode. Depending on your machine this is achieved by pressing a key like F2 or ESC during startup
3. When presented with the boot options choose to boot from the USB drive
4. In the Windows installer screen that shows up select your language and time settings and proceed.
5. In the next screen select repair my computer
6. Go to advanced options
7. Go to Command Prompt
8. Once the command prompt opens run the following command: diskpart
9. Now run list disk. This will list all the disk on your machine. It should look something like this:

DISKPART> list disk

| Disk ###| Status | Size | Dyn | Gpt |
| ------- | ------ | ---- | --- | --- |
|  Disk 0 | Online | 80GB | Yes | --- |

1. Select the disk you want to modify. In my example we use only one disk which shows up as Disk 0 so the command we're using is: select disk 0. You can choose which disk you want modified from the ones that show up in thee command executed above.

2. Run the following command clean This will clean your hard drive of all it's data.

3. At this point you will need to restart the command prompt in order to proceed. So close it by clicking on the X in the window, and reopen it by going through Repair my computer -> Advanced options -> Command Prompt as before
4. You will need to select your disk again so as before run: diskpart select disk 0
5. The next two steps might not be necessary but there are cases where clean does not remove the volumes on your disk so these will need to be deleted too. To list the volumes run the next command: detail disk 0
6. For each volume on the disk type: select volume= <volumenumber> and then delete volume
7. After that's done select the disk you want converted again select disk 0
8. Finally run convert basic

Congratulations your disk is now just a basic (b..) disk! You can proceed now with installing another OS on your machine just fine. You can:

1. Shut down your machine
2. Plug in the second USB drive with your desired OS
3. Install it :)

Many To Many relationship in Flask App using SQLAlchemy Flask-WTForm and QuerySelectMultipleField

In this example we'll be using two entities, post and categories for whom we'll be building a many to many relationship.

The many to many relationship adds an association table between the two model classes, this helper table is strongly recommended to not be a model but an actual table.

Let's start with our models:

models.py

categories = db.Table('categories',
                  db.Column('post_id', db.Integer, db.ForeignKey('post.id'), primary_key=True),
                  db.Column('category_id', db.Integer, db.ForeignKey('category.id'), primary_key=True))


class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    body = db.Column(db.String(250))
    categories = db.relationship('Category', secondary=categories,
                                  backref=db.backref('posts', lazy='subquery'))

class Category(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    category = db.Column(db.String(140))

The association table categories is a super simple table containing just two columns both ForeignKey references to the id's of the post and the category representing the connection between the two.

However just having an association table is not enough to connect the two entities together so the categories attribute in the Post model is added. Since this is a many to many relationship a secondary table is needed to be specified in the relationship, this is a reference to the association table. The back reference backref can be visualised like adding another field to the Category model.Lazy is set to subquery which just joins the two tables.

Remember to migrate and update your db after making alterations. flask db migrate -m "many to many"

flask db upgrade

Next let's move on to our forms. We'll be focusing on the form for creating a post and associating many categories to it.

forms.py

def possible_categories():
    return Category.query.all()

class PostForm(FlaskForm):
    body = TextAreaField('Say something', validators=[DataRequired()])
    categories = QuerySelectMultipleField('Categories', query_factory=possible_categories, get_label='category')
    submit = SubmitField('Submit')

How the QuerySelectMultipleField field works is that it will display a select drop-down field to choose between ORM results in a sqlalchemy query. For this the query_factory needs to be set to either a query or a function that returns ORM results, in our example the function possible_categories() is defined above that returns all the categories that are currently defined. For displaying we're using the category label as that will hold the category's name.

Moving on to the view function:

@app.route('/create_post', methods=['GET', 'POST'])
def create_post():
    form = PostForm()
    if request.method == 'POST':
        if form.validate_on_submit():
            new_post = Post(body=form.body.data)

            for categories in form.categories.data:
                new_post.categories.append(categories)

            db.session.add(new_post)
            db.session.commit()
            flash('New post added successfully!')
        else:
            flash_errors(form)
            flash('Blog post was not added.')
    return render_template('create_post.html', form=form)

Nothing too fancy here, we create a new post with the data inputted in the form, and then append each of the selected categories to it and save it in the db.

Lastly the html file. Simply:

create_post.html

<h1> Create A new blog post</h1>
<div class="row">
    <div class="col-md-4">
        {{ wtf.quick_form(form) }}
    </div>
</div>

The implementation of the create category form and view goes along the same lines so I'll leave it for the readers homework.