data flow expr()

Question

Hi,
I am trying to pull the expression string from a cash table but error is:
Error:
Cannot evaluate constant value with this type
What am I doing wrong in the value expression?

Answer 1

Hello @arkiboys ,

Thanks for the question and using MS Q&A platform.

I had checked internally, the below are possible :

1. expr(‘String’)
2. expr(String parameter) Note : This is presented in the video.

expr(string returning function) – NOT SUPPORTED

Now coming back to your scenario and considering your above constraints. (I am assuming this is a follow up query of what you had in this thread https://learn.microsoft.com/en-us/answers/questions/617827/index.html )

I came with an alternative which may meet your requirement.

You could pass the expression and table name as a parameter to the dataflow. Details of the implementation are below :

You could do a lookup to the table (csv) - which contains the TableName, columnName, ApplyExpr

Now for each Row (within foreach activity),

I am setting the variable associated with each column so that I could process the TableName, columnName, ApplyExpr. (Note : You could also - directly used item().<value> - This is for convenience & not a mandate step)

This is the Set Variable of the FinalExprr

This basically does this transformation string operation - converts to Apply Expression and column name to necessary expression format that can be processed at the data flow end
action(columname). (Note : If your transformation doesn't follow this format, you could do an if condition - format it as per each action. )

You could pass the parameter to the dataflow - tableName and Final expression (this is combination of the columnName & ApplyExpr)

For instance, if your table had the below row

table1.csv,value,upper

Then the parameter to the dataflow will be

table : table1.csv
expression : upper(value)

Now inside the Dataflow , I am evaluating the parameter as an expression below.

I am dynamically setting the source using the $table parameter.

Hope this will help. Please let us know if you have any further queries.

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Answer 2

Hi @arkiboys . Have you solved this problem. Today i am facing same problem. My requirement is same as your this requirement.

Please help.