Collectives™ on Stack Overflow
Find centralized, trusted content and collaborate around the technologies you use most.
Learn more about Collectives
Teams
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
Learn more about Teams
Sqlalchemy.exc.InvalidRequestError: session in prepared state
I have built a social media like webapp which through infinite scrolling uploads more posts as you scroll.
Though if I like a post as I am scrolling I get errors while in development mode.
I am using python/flask for backend.
If I scrolling my feed and simultaneously liking a post I get, in development mode, the errror
"sqlalchemy.exc.InvalidRequestError: This session is in 'prepared' state; no further SQL can be emitted within this transaction."
This has so far only happened in development mode and not in production mode but I am afraid that it will be a problem if more people start to use it.
Is this an error that will only be a problem in development or will this come up in production as well if I get a significant amount of users?
I have tried incorporating try except statements in my backend code which takes care of the error but it leads to other error so I would like to know if this is a problem that will be a larger issue later on or if it is only a problem in development?
Thanks
I tried adding a reproducible example but it was quite difficult
Beginning with the infinite scrolling.
In this case I began by loading the indexes of the different posts
Front end
<div class="flow">
<div class="flowpost" v-for="post in postlists" :key="post.id" >
<PostTemplate :iterated_list ="post.id" ></PostTemplate>
where postlists contains the id of the different posts
Script
mounted(){
window.onscroll = () => {
let bottomOfWindow = document.documentElement.scrollTop + window.innerHeight === document.documentElement.offsetHeight;
if (bottomOfWindow) {
this.addmore()
The method addmore calls the get_index_list_of_posts function to load more posts
Backend
def get_index_of_list_of_posts():
user_id = request.args.get("userid")
group_action_id = request.args.get("group_action_id")
page_nr = request.args.get("page_nr")
total_pages = 0
result_dict = {}
other_posts_query__ = Session.query(mvpUsersToPosts.id).filter(mvpPosts.id==mvpUsersToPosts.mvp_posts_id ).order_by(mvpPosts.datetime.desc())
pagettt = Paginator(other_posts_query__, 4)
p = pagettt.page(page_nr)
post_query = p.object_list
result_post = []
postlist = []
for post in post_query:
result_post = {
"message":message,
"id": post[0]
postlist.append(result_post)
result_dict_list = {}
result_dict_list["posts"] = postlist
result_dict_list["current_page_nr"] = page_nr
result_dict_list["total_page_nr"] = total_pages
posts_result = json.dumps(result_dict_list)
return posts_result
I then fill the posts with its data by calling the following backend function from the PostTemplate component.
def get_postlista_to_posttemplate():
userid = request.args.get("userid")
postid = request.args.get("postid")
result_post = []
postlist = []
post_query = Session.query( mvpPosts,mvpUsers, mvpUsersToPosts,mvpSolutionTags).filter(mvpUsersToPosts.userid == mvpUsers.id ,mvpUsersToPosts.mvp_posts_id == mvpPosts.id, mvpUsersToPosts.id ==postid, mvpPosts.id==mvpPostsToSolutionTags.mvp_posts_id, mvpSolutionTags.id==mvpPostsToSolutionTags.tagid).all()
get_total_liked_query = Session.query( func.sum(mvpliked.liked)).filter(mvpliked.postid == postid).all()
for post, users,user2post, tag in post_query:
result_post = {
"postid": user2post.id,
"mvp_post_postid" : post.id,
"posttitle":post.posttitle,
"posttype":post.posttype,
"postimage":post.postimagevideo,
'postliked':is_liked,
postlist.append(result_post)
posts_result = json.dumps(postlist)
return posts_result
The prepared state error occurs by the get_total_liked_query which I then wrapped in a try/except statement which did not help.
I can then like a post which is done with the following backend function.
def like_post():
reply = request.get_json()
post_id = reply["post_id"]
user_id= reply["user_id"]
like_query = Session.query(mvpliked.liked).filter(mvpliked.postid == post_id, mvpliked.userid == user_id ).distinct(mvpliked.postid).all()
if len(like_query) ==0:
newrow = mvpliked(postid = post_id, userid = user_id, liked=1)
Session.add(newrow)
Session.commit()
else:
if (like_query[0][0] == 1):
like_value = 0
else:
like_value = 1
Session.query(mvpliked.liked).filter(mvpliked.postid == post_id, mvpliked.userid == user_id ).update({mvpliked.liked: like_value })
Session.commit()
return ""
The invalidrequest error seem to occur when functions like_post() and get_postlista_to_posttemplate() run simultaneously.
Session code
engine = create_engine(DATABASE_URL_prod)
Base = declarative_base(engine)
def loadDatabaseSession():
Base.metadata.create_all(engine)
DatabaseSession = sessionmaker(bind=engine)
DatabaseSession = DatabaseSession()
return DatabaseSession
Session = loadDatabaseSession()
–
–
–
–
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
