Merge 2 collections on a condition to populate a nested collection - blueprism

Question

I have 2 collections in which I get data from DB.
Collection 1 column names: A_id, Bid, PCid, Bname ==> all text fields
Collection 2 column names: A_ref, Cid, Cname, value ==> all text fields
Collection 1 and 2 are related based on collection1.A_id=collection2.A_ref
I have a 3rd collection which is a nested collection:
Collection 3 Column names: action(text), colA (collection)
colA column names: Bid(text), PCid(text), Bname(text), colB (collection)
colB column names: Cid, Cname, value ==> all text fields
I want to join collection 1 and collection 2 based on mentioned condition to load the nested collection 3.
Please help.
I have tried using the collection VBO but didnt succeed. I also tried using a nested loop stage and counters with a decision stage but my code fails to add empty row to the nested collection before populating the values.
Using Blueprism stages
I want to join collection 1 and collection 2 based on mentioned condition to load the nested collection 3.
I am using a nested loop stage and counters with a decision stage but my code fails to add row to the nested collection.

Answer 1

Aswin, please check the solution below:
For further information, i will pass the XML file as for you to import to Blue Prism and check every stage, since it would require a lot of time and screenshots to explain everything. Plus you will have a clear understanding of every step in your environment.
Download XML file from my github repository link:
Blue Prism Merge Collections to populate a nested-collection
Hope these information will be useful.

Answer 2

I believe what you're looking for is what I call a "box join". You'll need a code stage.
Inputs:
Main (collection)
Nested (collection)
Main Key (text)
Nested Key (text)
New Field Name (text)
Outputs:
Output Collection
Code:
' Check for requirements: key columns exist, and that the new field to create in the main
' collection does not already exist.
If Not Main.Columns.Contains(Main_Key) Then
Throw New Exception("Main Collection does not contain the key column '" & Main_Key & "'")
Else If Not Nested.Columns.Contains(Nested_Key) Then
Throw New Exception("Nested Collection does not contain the key column '" & Nested_Key & "'")
Else If Main.Columns.Contains(New_Field_Name) Then
Throw New Exception("Main Collection already contains a field named '" & New_Field_Name & "'")
End If
' Add the column containing the DataTable which will be populated with data from the Nested collection.
Main.Columns.Add(New_Field_Name, GetType(DataTable))
For Each MainRow As DataRow In Main.Rows
' Create the new nested table for this row and populate the column names.
Dim Table As New DataTable
For Each NestedColumn As DataColumn In Nested.Columns
Table.Columns.Add(NestedColumn.ColumnName, NestedColumn.DataType)
Next
' Because we don't want to copy the key column.
Table.Columns.Remove(Nested_Key)
' Check each row in the Nested collection to see if it matches current key.
For Each NestedRow As DataRow In Nested.Rows
If MainRow(Main_Key) = NestedRow(Nested_Key) Then
' Got a match; add the row from Nested into the new table.
Dim NewRow As DataRow = Table.NewRow
For Each TableColumn As DataColumn In Table.Columns
NewRow(TableColumn.ColumnName) = NestedRow(TableColumn.ColumnName)
Next
Table.Rows.Add(NewRow)
End If
Next
' Set the nested collection
MainRow(New_Field_Name) = Table
Next
Output_Collection = Main
Using the example from the question, you'll want to pass the following into the code stage inputs:
[Collection 1] -> Main
[Collection 2] -> Nested
"A_id" -> Main Key
"A_ref" -> Nested Key
"colB" -> New Field Name
The resulting Output Collection will contain the fields from Collection 1, with an added column "colB" which contains the fields (excluding the key) from Collection 2. From there, a calculate stage can get the results into Collection 3.