Join Tool on String Fields Yield "String fields can only be joined to other string fields"

[ASMR]

I am trying to join two data streams on the fields Sold-to party (coming from the left) and SAP ID (coming through the right). Used to be fine, then this morning I'm all of a sudden receiving this error message:

So I went to Tool 312 to investigate the issue:

Then I added a Select tool right before the Join tool for each the left and right side of the incoming data, to ensure that each joining field is set to a string data type:

I figured this would resolve but issue, but alas I keep getting the same "Strings join to strings" error message when saving the workflow to the Gallery. Any ideas as to why this is happening and what might be the fix? I've already tried deleting the Join tool and replacing it with a new on, but to no avail. 

Update: I changed each field's data type to "String" before the join, and that worked. So why doesn't it work with "V_String"?

[afv2688 · Accepted solution]

Hello @ASMR ,

Have you tried to force the field to be what you want?:

You can do this on the select tool. This option only appears when the incoming field arrives already with the desired data type (doesnt matter which):

Regards

[ASMR]

This worked! I changed just SAP ID to "V_String Forced" and the join now doesn't give that error. Do you have any idea as to why it works? What exactly is the difference between V_String and V_String Forced?

[afv2688]

On the select tool, what you usually see are two different selections of data types, with white background or with red background.

If the background is red it means you are forcing the data that is coming into the tool to change to this data type.

But what happens if the data arrives already in the desired format? You will only see it as a description, showing the input with a white background. That means, that if by some chance you get the data next time and the column is 'double' data type, the flow will change it.

If you force the data type, you are telling the application what it has to be, no matter what, it is not allowed to be switched to another.

Hope I have explained myself :S

Regards