How to update 2 CDT's with each other values in a process model

Question

I am new to Appian. Still learning the basics. 
 I have two tables 
 1. Attachments - for adding attachment relate details like fileId,fileName, fileExt, fileSize etc and 
 2. AttachmentDetails - for description, comments etc 
 Below is the requirement - 
 When i upload a document I save them to the attachment table with attachmentDetails primary key (attachmentDetailsId) 
 After the documents are saved in the attachment table I need to save the attachment tables primary key (attachmentId) to the attachmentDetails table 
 The problem is i am not sure how to update when there are multiple attachments. 
 For Example - If i upload 2 attachments and update attachmentDetails 
 Attachments Table

attachmentId 
 fileId 
 attachmentDetailsId

1 
 123 
 1

2 
 234 
 2

Attachment Details Table

attachmentDetailsId 
 Description 
 attachmentId

1 
 Evidence 
 1

2 
 Tracker 
 2

I will first save the 2 attachmentDetails (array) to the db first. (at this point attachmentId will be null and I will have the attachmentDetailsId's) 
 Before saving the attachments to the table i need to map each attachment with attachmentDetailsId. How do i map attachmentDetailsId-1 with first attachment and attachmentDetailsId-2 with second attachment? 
 After I map the above I will save them to the attachments table (at this point I will have the attachmentId's) 
 How do i now map attachmentId-1 to the attachmentDetailsId-1 and How do i now map attachmentId-2 to the attachmentDetailsId-2?

virat yogi · Accepted Answer

Hi, if there is one to one relationship I can't think of any use case where we need to maintain two tables. But in case you want this and there is some use case for the same. Below is one of the possible ways to do it 
 
 a!localVariables(
 /* Assuming this to be the initial state */
 local!attachment: {
 {
 attachmentId: null,
 fileId: 123,
 attachmentDetailsId: null
 },
 {
 attachmentId: null,
 fileId: 234,
 attachmentDetailsId: null
 }
 },
 local!attachmentDetail: {
 {
 attachmentDetailsId: null,
 Description: "Evidence",
 attachmentId: null
 },
 {
 attachmentDetailsId: null,
 Description: "Tracker",
 attachmentId: null
 }
 },
 /* Wrtitng local!attachmentDetail to database using write 
 to datastore entity will give back the Ids for the same */
 local!attachmentDetailAfterWrite: {
 {
 attachmentDetailsId: 1,
 Description: "Evidence",
 attachmentId: null
 },
 {
 attachmentDetailsId: 1,
 Description: "Tracker",
 attachmentId: null
 }
 },
 /* We can use below to map the attachment detail in the
attachment table
*/
local!attachmentBeforeWrite: a!forEach(
 items: local!attachment,
 expression: updatedictionary(
 fv!item,
 {
 attachmentDetailsId: property(
 index(
 local!attachmentDetailAfterWrite,
 fv!index,
 {}
 ),
 "attachmentDetailsId",
 {}
 )
 }
 )
 )
 
/* You can then write the attachment to database thus generating
the Ids for the same and then use the similar way to map
atatchment Ids to the attachment detail 
*/
) 
 
 The output of the mapping forloop will be something like this 
 
 Hope it helps

kaushikr0003 · Answer

Thanks viraty this worked for me.

How to update 2 CDT's with each other values in a process model

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