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Helper I
Helper I

Ebay style app: how to manage concurrent user sessions ?

I'm creating an ebay style app: 1 product to sell, 3 pieces available but 10 possible buyers.

Each buyer can buy max 1 item.


DB: I have a list in sharepoint with the yes/now column of the product to sell.

CLIENT: I created the app where you see the yes/no check and you can choose to buy or not. I added a label showing how many pieces are available (3 minus count of shp list column).

I have a countdown timer that refreshes the source every 2 secs so that the remaining pieces field is always updated.

Now I thought I could do a check before submitting the form so that it does not patch the list if the product is finished during the latest 2 secs.

What if 2 concurrent users click on submit ? Is there a kind of special powerapps function / caveout to avoid "overbooking" ? 



Super User III
Super User III

This could be done as follows:

  1. Insert  Dropdown1 or Combobox1 set it Items to ProductTable.ID (Assumed that Product have unique Column)
  2. Insert a ProductNameTextbox (To pick Product users will select from dropdown1. if you are using a form, then instead of inserting another TextBox, use one of the datacardvalues on your form.
    Put this formula in the Default of the Textbox/datacardvalues: Dropdown1.Selected.ID
  3. Inset Textfield to a lookup: LookUp(ProductTable, ID= Dropdown1.Selected.ID,Balance)
    Thus whenever an ID is selected, it picks its corresponding Balance from the datasource
  4.  We can the put a formula on the OnSelect button to check if Balance is less or More

    If you like this reply, please give kudos. And if this solves your problem, please accept this reply as the solution.

    Give it a trial. Details of your datasource would help

I don't see where concurrent sessions are managed.

I was actually thinking of having another sp list with the products availability where the sp column is a number where the minimum possible value is zero (see sample below).

I expect that when you try to reduce that value you got a kinda error which I could pick up from powerapps.

If error, no patch.

Any idea to catch that error ?

I found this below but it's not catching anything.

If( IsEmpty( Errors(ProductList, Patch(ProductList, ... 







I would also need a way to decrease the value without calculating it's existing value.

I mean, if I click on submit and the current value is 3, my submission will say "3-1=2" and it will be ok.

If someone else clicks on submit in the exact same moment the current value will still be 3, and his submission will also say "3-1=2" and it will be accepted too cause it won't raise any error since it's not minus zero (still if I solve the error issue above).

Now, instead of having to calculate the current remaining, can I just trigger the decrease ?

I mean, when I click the formula should say "decrease that", not "grab the current value, remove 1 and update it". (I hope I explained myself)

It looks like somebody asked if I solved the issue but the question was removed.


So I first had a working situation like below but it got **bleep**ed up somehow.

I had two lists, one with users and a yes/no column for any product chosen and another list with the maximum pieces available.

By using the oncheck and onuncheck fields of the toggles, I could do:

- oncheck: if no error while patching the list of available pieces and reducing the max available number by one (minimum allowed number is zero), then patch also the yes/no field of the first list for current user.

- onuncheck: just patch both list by adding a 1 to the available pieces and set the right yes/no value on the other one.


But it worked for maybe 2 mins then buum !!!

Really no idea what's going on


I'm back to the countif solution now. I wish this thing was open source..


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