I haven't looked at your code in detail, so this may not be the cause
of the problem, but in general it is a bad idea to modify a collection
while you are iterating over it. ie. this is not generally safe:
for tag in edit_post.tags:
edit_post.tags.remove(tag)
Removing the tag from the "tags" list will confuse the "for" loop.
Instead, you should probably iterate over a *copy* of the list:
tags = list(edit_post.tags)
for tag in tags:
edit_post.tags.remove(tag)
>From a performance point of view, that's not a great pattern -
edit_post.tags.remove(tag) requires searching the list to find the
item to remove. You might be able to get away with simply writing:
edit_post.tags = []
...depending on how the association proxy is set up. You might also
want to consider using a collection class other than a list here.
Since you want each string to only appear once in the collection, a
set() might be a better choice.
Finally, unless you are doing something special in your Tag()
constructor, this code is going to create new Tag objects even if a
Tag with the same description is already in the database. If this
isn't what you intended, you might want to investigate one of the
approaches at
https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/UniqueObject.
Hope that helps,
Simon
On Sun, Feb 22, 2015 at 9:27 PM, Asad Dhamani <[email protected]> wrote:
> I looked at my code some more, and found a now obvious mistake. I changed my
> code to:
>
> def edit(id, tags=None):
> edit_post = Post.query.get(id)
> if tags is not None and tags != "":
> for tag in tags.split(','):
> tag = tag.strip(" ")
> if tag not in edit_post.tags:
> add_tags = Tag()
> add_tags.text = tag
> edit_post.tags_relationship.append(add_tags)
> db.session.add(add_tags)
> db.session.commit()
> for tag in edit_post.tags:
> if tag not in tags:
> edit_post.tags.remove(tag)
> db.session.commit()
> else:
> for tag in edit_post.tags:
> edit_post.tags.remove(tag)
> db.session.commit()
>
> However, now if I remove all the tags from a post, a last one remains, and I
> have to remove it again to get rid of all the tags.
>
> On Monday, February 23, 2015 at 1:46:07 AM UTC+5:30, Asad Dhamani wrote:
>>
>> I have a many-to-many relationship in my models. This is what they look
>> like:
>>
>> class Post(db.Model):
>> __tablename__ = 'Posts'
>> id = db.Column(db.Integer, primary_key=True)
>> tags_relationship = db.relationship('Tag', secondary=tags,
>> backref=db.backref('posts', lazy='dynamic'))
>> tags = association_proxy('tags_relationship', 'text')
>> full_text = db.Column(db.Text, nullable=True)
>> fulltext_vector = db.Column(TSVectorType('full_text'))
>>
>>
>>
>> class Tag(db.Model):
>> id = db.Column(db.Integer, primary_key=True)
>> text = db.Column(db.String(255))
>>
>>
>> tags = db.Table('tags',
>> db.Column('tag_id', db.Integer, db.ForeignKey('tag.id')),
>> db.Column('post', db.Integer, db.ForeignKey('Posts.id'))
>> )
>>
>> I need to add the ability to edit tags. I know how to add tags:
>>
>> def edit(id, tags=None):
>> edit_post = Post.query.get(id)
>> if tags is not None and tags != "":
>> for tag in tags.split(','):
>> tag = tag.strip(" ")
>> if tag not in edit_post.tags:
>> add_tags = Tag()
>> add_tags.text = tag
>> edit_post.tags_relationship.append(add_tags)
>> db.session.add(add_tags)
>> db.session.commit()
>>
>> This is what I'm doing for removing tags:
>>
>> for tag in edit_post.tags:
>> if tag not in tags:
>> edit_post.tags.remove(tag)
>> db.session.commit()
>>
>> However, I can not delete the last remaining tag from a post. Once I add a
>> tag, it seems like there has to be a minimum of 1 tag on that post, as I can
>> add more, and I can remove all but the last remaining tag.
>>
>> What am I doing wrong?
>
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