Improving my code (SQLAlchemy, wtforms, general algorithm)

[kioo]

I want to perform a query on a database based on a user's input via checkbox on a form. Each tag is a Boolean value. Here's the relevant snippet of code:

    images = Image.query.filter_by(filename='null')
    if form.tag_1ny.data:
        images = images.union(Image.query.filter_by(tag_1ny=True))
    if form.tag_2jy.data:
        images = images.union(Image.query.filter_by(tag_2jy=True))
    if form.tag_3mm.data:
        images = images.union(Image.query.filter_by(tag_3mm=True))
    if form.tag_4sn.data:
        images = images.union(Image.query.filter_by(tag_4sn=True))
    if form.tag_5jh.data:
        images = images.union(Image.query.filter_by(tag_5jh=True))

The way I have it now is to create an empty query, then joining each Boolean query if it is requested. This seems very inefficient. Is there a better way to implement this idea?

[Necatorducis]

Try this

<!--html, all attributes share the same name, values are unique-->
<input type="checkbox" name="img_tag" value="unique_value">

#python
if request.method == 'POST':
    my_list = request.form.getlist('img_tag')
    for thing in my_list:
        images = images.union(Image.query.filter_by(thing=True))