Help with cascading combo boxes


I've only been using outsystems 2 weeks and completed bootcamp last week but I'm really stuck trying to implement 2 combo boxes where the second 1 is dependant on the first 1. 
If I try without the cascading I can select from the 2nd box and the value is stored but if I try to implement then no value pulls through until I do the refresh and then the selected value isn't stored.

I've tried to find guidance on here but there doersn't seem to be an easy way to do this.

Any help would be much appreciated.

Can you explain what you mean by "stored"?  Is the 1st or 2nd combo box bound to enitity attributes or are they being used as filters for a page or ??
by stored I mean .. when the record is saved the value in the second combo is stored in the database. As soon as I try to implement the cascading side of it the value in the database doesn't pull through to the second combo box.
I have tried creating a local variable record list and assigning the records to it then binding the second combo box to this record list buu I keep 'breaking' it. I can send the file if that would help?

Hi Debra.

Could you upload your example so we can take a look and try to figure out what's happening?


Best regards,

Tito Azevedo.

I've attached the oml
After a quick review, I am having trouble understanding why you refer to the combo boxes as cascading. It looks like your combo boxes are just foreign keys into reference entities. I may be missing the point of your data. If I am accurate that one combo box is not dependent on the selection of another, I would suggest removing all of the queries that occur on any table other than the "Opportunity" table. The combo box will perform without querying their source entities.
I'll try and explain why I think they are cascading ...

I have an entity 'OppTypeSalesStage' which creates the link between the 'Opportunity Type' and the 'Sales Stage' entities. I have a form which allows this link to be made.
On the Opportunity Details screen, if the user changes the Opportunity type to 'Formal Tender' then only 'Pre contract Award' should show in the Sales stage combo. If the user selects 'Proposal' then the 'Sales Stage' combo should show 'Stage 1' and 'Stage 2'. 

I hope that makes sense. 
Okay, I got it. I have tried refreshing entities for bound entity attributes and did not have any positive results. From what I see, I think the issue is in your data model where you have the joins in a circle. This may cause issues of data integrity. For example, if you have a record with ‘Formal Tender’ and ‘Pre Contract’, when a user changes the Opportunity Type then the current value of the Sales Stage will have referential integrity issues, because ‘Pre Contract’ key is not a valid key based upon filtering by the Opportunity Type.   My humble opinion is to suggest changing this area of your data model to something like, making SalesStage a child of OppTypeSaleStage or other model that fits your business need.