Looping a nested DataTable within a Datatable

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1

Hi,

I’d really appreciate any help with this one.

The process looks to gather information for on-boarding and its currently built up around a main datatable (dt_Master1) which contains a few other datatables; fname & sname, along with some other string columns such as joining date.

dt_Master1:
dt_master1

dt_fName:
dt_fName

dt_sName:
dt_sName

My issue is that i cannot seem to loop through the information gathered with a simple write line without getting an error:

m_forEach

expression
expression766×465 13.4 KB

The error received: For Each Row in Data Table: Unable to cast object of type ‘System.DBNull’ to type ‘System.Data.DataTable’.
unableToCast

Any help will be greatly appreciated. Thanks in advance

2

the error comes from the following:
the looped row column fname / sName is null, so it cannot convert

for inspections we would recomment to use the immediate panel
Understanding the 6 Debugging Panels of UiPath in the easiest way possible! - News / Tutorials - UiPath Community Forum

for tracings / understandings

  • loop over a test data datatable which is prepopulated in advance

for handling empty column values if it will occur or not

use within the for each row:

IF(isNothing(CurrentRowMaster("fname") orElse isDBNull(CurrentRowMaster("fname")), new DataTable(), Ctype(.....))
3

Hi, thanks for your quick reply.
I’m a bit confused as i’m looping through the test data provided in the screen shots… so i’m confused as to how the values could be null?

Thanks

4

as mentioned above all can be verified, inspected when debugging and using the immediate panel. Here you can fire several statements for inspections

5

I’ve watched the video & i’m none the wiser.

I can see the datatables are populated - why are they coming up as null? Should i be using another method to read the data?

locals
locals942×722 18.2 KB

Thanks

6

as mentioned use the immedediate panel e.g.

  • set a breakpoint within the for each body e.g. write line activity
  • debug and get paused
  • immediate panel: CurrentRowMaster(“fName”)

Kindly note:
grafik

[ ] is about empty tablename property value
7

I feel as though we’re talking at cross purposes here.

I have created a duplication of the work that’s in production. All the datatables have test data in them. I’m just trying to understand why the fName datatable is showing as Null. I can see that it’s null in the locals table & that it’s null in the original error message. What i’m trying to understand is why it is null and how I can go about accessing the nested rows, which should be present.

I have attached a copy of the project. Please help.

Thank you.

Nested DataTables.zip (3.2 KB)

8

pattyricarte / sharique.khan / Palaniyappan would either one of you be able to help please?

9

@qwerty1
Kindly note from your shared Implementation:

grafik
grafik685×858 45.1 KB

As the Master will not have populated the fName, sName columns so the CType is failling. We mentioned above how to catch:

grafik
grafik937×128 23.6 KB

IF(isNothing(CurrentRowMaster("fname")) orElse isDBNull(CurrentRowMaster("fname")), dt_fName.Clone, Ctype(CurrentRowMaster("fname"), DataTable))

and for the exploration on how it will handled the populated column we can prototype:

Population:
grafik

Access:

grafik
grafik913×131 19.4 KB

So lets summarize:

  • with a defensive null check we can handle empty column values
  • When the data column is correct populated we can convert and use it for the loop
    grafik
10

@Palaniyappan would you be able to offer some help here?

Can you tell me how i’d go about adding data to dtMaster1?
For example, i’d like to add a distinct ID and Joining date, but then multiple names to both dt_fname & dt_sname. When i try to copy the names from dt_fname & dt_sname in to dtMaster, all the names are added to one ID, rather than separate.

A standard Add DataRow Activity doesn’t seem to work - any ideas?

Thank you in advance