I don't think there's a configuration option for this, so you would have to apply custom code.
The simple way:
First, a new field - call it something like Association_Count. Then have an Active Link that counts the number of rows in the z2TH Associations table field (I think?) and sets that field: use the COLCOUNT() function. Have the AL trigger on the button z3Btn Search Associations.
Then, when someone tries to add a new one, the AL triggers and the count field is set. If it equals 20, you pop an error message.
Of course, if you go to another Incident, there's nothing stopping you from associating to the one that already has 20 records.
Complex (proper way):
Have filters on the HPD:Associations form that trigger when a new record is being submitted that counts the number of associations for both that form's Request ID01 and Request ID02 fields. You would also need a count field.
So, SELECT COUNT(*) FROM HPD_Associations WHERE Request_ID01 = '$Request_ID01$'
Set the Count field to the result - if already at 20, pop an error.
Do the same for Request ID02.
Thank you Steve for your time and valuable inputs Really appreciate for sharing the type we can do in detail Thank You again!!
Thank you Siva for your input