# How to make sure something is written to the db before continuing?

**URL:** <https://forum.djangoproject.com/t/how-to-make-sure-something-is-written-to-the-db-before-continuing/14550>\
**Category:** Mystery Errors\
**Created:** [June 30, 2022, 6:38am UTC](https://forum.djangoproject.com/t/how-to-make-sure-something-is-written-to-the-db-before-continuing/14550 "2022-06-30T06:38:35Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![xtlc](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/xtlc/32/3887_2.png) [@xtlc](https://forum.djangoproject.com/u/xtlc)\
**Post date:** [June 30, 2022, 6:38am UTC](https://forum.djangoproject.com/t/how-to-make-sure-something-is-written-to-the-db-before-continuing/14550/1 "2022-06-30T06:38:35Z")

</div>

I have a strange problem, that I can reproduce every 4-6th try and I failed so far to understand how to avoid it:

Somewhere in my django code there is a function that imports a CSV file to the database of products, and from these products I create images with the price on the image - and sometimes an old price is used:

```auto
def batch_update_products_in_db(working_file, store, delimiter = ";"):
    with open(working_file, encoding = "utf-8") as inputfile:
        reader = csv.reader(inputfile, delimiter = delimiter)
        for row in reader:
            try:
                productdata = {header[i]: row[i] for i in range(1, len(row))}                
                product = Product.objects.get(store = store, number = row[0])
                if product.data == productdata:
                    continue
                else:
                    product.data = productdata
                    print("TEST 1:", product.data)
                    product.save()
                    update_product_in_db(product)
            except Product.DoesNotExist:
                Product.objects.create(store = store, number = row[0], data = productdata)
            except Exception as E: 
                log(...)

```

in this function there is a call to another function that generates these images:

```auto
def update_product_in_db(product):
    def do_update(task):
        links = Link.objects.filter(products = product)
        
        ## get all link objects for this product:
        for link in links:
            product_pks = [p.pk for p in link.products.all()]
            product_qs = Product.objects.filter(pk__in = product_pks)
            if product_qs.exists():
                img = generate_img_from_layout(link.layout, product_qs)["object"]  
               ...
        task.timestamp_end = timezone.now()
        task.is_done = True
        task.save()

    task = BigTask.objects.create(name = "update products in db")
    t = threading.Thread(target = do_update, args = [task])
    t.setDaemon(True)
    t.start()   
    return {'id': task.id}

```

where I stripped down the `generate_img_from_layout()` function to just output the product:

```auto
def generate_img_from_layout(layout, product_qs)
    for product in Product.objects.filter(pk__in = products):
        print("Test 2:", product.data)

```

and in the console when uploading multiple csv files (one after each other) I get the output:

> Test 1: {‘name’: ‘hellotest’, ‘price’: ‘16.90’}  
> Test 2: {‘name’: ‘hellotest’, ‘price’: ‘16.90’}
> 
> Test 1: {‘name’: ‘hellotest’, ‘price’: ‘16.91’}  
> Test 2: {‘name’: ‘hellotest’, ‘price’: ‘16.91’}
> 
> Test 1: {‘name’: ‘hellotest’, ‘price’: ‘16.92’}  
> Test 2: {‘name’: ‘hellotest’, ‘price’: ‘16.92’}
> 
> Test 1: {‘name’: ‘hellotest’, ‘price’: ‘16.93’}  
> Test 2: {‘name’: ‘hellotest’, ‘price’: ‘16.92’} #######
> 
> Test 1: {‘name’: ‘hellotest’, ‘price’: ‘16.94’}  
> Test 2: {‘name’: ‘hellotest’, ‘price’: ‘16.94’}

So at some point the `product.save()` apparently did not finish before the next `Product.objects.filter()` reads the product again.

So after posting a similar example to stackoverflow ([here](https://stackoverflow.com/questions/72182990/objects-getid-id-only-works-randomly?noredirect=1#comment127537261_72182990)) I tried to change the code of `batch_update_products_in_db()` to:

```auto
...
print("TEST 1:", product.data)
product.save()
transaction.on_commit(lambda: update_product_in_db(product))
...

```

but this resulted in the `update_products_in_db()` function not to be called at all. Where did I take a wrong turn?

---

<div class="post-metadata">

**Author:** ![KenWhitesell](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/kenwhitesell/32/280_2.png) [@KenWhitesell](https://forum.djangoproject.com/u/KenWhitesell)\
**Post date:** [June 30, 2022, 1:04pm UTC](https://forum.djangoproject.com/t/how-to-make-sure-something-is-written-to-the-db-before-continuing/14550/2 "2022-06-30T13:04:56Z")

</div>

> [@xtlc](#):
>
> ```auto
> task = BigTask.objects.create(name = "update products in db")
> t = threading.Thread(target = do_update, args = [task])
> t.setDaemon(True)
> t.start()   
> 
> ```

This is something you **never** want to do in Django. You do not control the process or the db connection that your view is running in.

Either do this synchronously in line in your view, or dispatch it to a separate worker process using something like Celery.