Nested CDTs

Question

I wanted to know what's Appian best practices when it comes to nested CDTs. How many levels deep should a CDT be nested? What are the draw-backs of nesting too deep? Are there any advantages of creating a view and mapping it to CDT instead of doing a nested CDT? Any input on this is greatly appreciated. Thanks.

chandu · Accepted Answer

Hi Jamal, 
As u aware that Appian recommends one level of nested CDT. As far as i know these are the following are the limitations . 
if you want to get only parent cdt data, you will get child cdt data as well.In one to many relation ship this results in pulling unnecessarily child data as well. 
Additional coding needs to be done to show the data in grids/reports that is coming from nested CDTs[typically when not in one one relationship] 
[Need to confirm the below Usecase showing the nested CDT in script task output tab] 
Suppose you a have a nested CDT structure as below. 
CDT1 
	field1InCDT1 
	CDT2 
 field2InCDT2ofCDT1 
 CDT3 
 field3InCDT3ofCDT2ofCDT1 
 
In script task outputs tab, I think you cannot store a value into the field CDT1.CDT2.CDT3.field3InCDT3ofCDT2ofCDT1 as Outupt tab will show two levels deep only. 
 
I'm really interested in digging more on nested CDT's. Lets see what other practitioners suggests.

ankita0004 · Answer

Nested CDT has some advantages as well as some limitations also. 
 
Advantages: 
 
1. There is no need for creation of view if we use nested cdt. 
2. We can fetch data of child cdt from parent cdt 
 
Limitations: 
 
It has much more limitations than advantages: 
 
1. Debugging of process instance is much difficult. 
2. We can't give a name of column in master table. 
3. Unnecessarily we need to fetch child table data

and many more disadvantage So View is much better approach than nested cdts.

John M · Answer

Jamal, 
 
According to the playbook they should not be more than 1 level deep ( community.appian.com/.../project-implementation-best-practices-checklist) . You can also find a list of db best practices here ( community.appian.com/.../database-performance-best-practices) which discusses some drawbacks of using nested cdts

aloks0189 · Answer

Adding to above points, also when you are working with Nested CDT, you might face difficulties in many aspect such as, 
 
While converting this data, to JSON and getting the dictionary back from JSON, will be pretty difficult. 
 
Also when you want to debug these data in UI or process model, it will be difficult while compared to normal CDT. 
 
And I believe, we should not go for nested CDT even for single level, if we have any other choice remain, 
 
yes I agree, as per Appian statement, upto 1 level of nested is ok or good, but I believe Appian suggests, if at all you want to go for nested CDT then go for 1 level but I believe if you can achieve the same using plain CDT, then you should always go for plain CDT

vineeta6579 · Answer

One of the disadvantages of nested CDT design is N+1 Problem, Ref below doc link for details. 
 community.appian.com/.../database-performance-best-practices 
 database performance best practices

smriti p0001 · Answer

Appian generally recommends one level only, but in real time scenario specially when you are using services then lot of nesting is required, however it may lead to performance issues later.