SSIS Variable Scope

Question

Why would you define a SSIS Variable to a Scope? To a specific container, task?

I mean when I define variables they are unique. Like for instance in a Foreach Loop Container, the Collection and variables are unique to it. So why would I change the Scope to indicate that? Seems kind of redundant.

Maybe I'm missing the purpose of Scoping SSIS Variables to a specific container task.

Can you explain that to me?

Answer 1

Scoping, like in programming, is useful for controlling the lifetime of a variable. You might not use every scope in every package but the option is there if you need it.

The For Each container is probably the easiest to understand and one of the more common. You are processing a set of data in a loop. Each time through the loop you are setting some variables based upon the current value being iterated. You would define these variables at the container level so that each time through the loop their values are reset. If you had scoped them higher, say at the package level, then you would need to ensure that each time through the loop you "reset" all the variables otherwise you may end up using a value from a previous iteration.

But what if you need to run 2 For Each loops in parallel and they may share data? In that case you might wrap them both in a higher level container and set the shared variables at that level.

A task level variable would be needed less often but could be useful if your task needs a value in several places but that value is calculated using an expression. Rather than recalculating it each time you could use a variable to calculate it once and then have the task use the variable. To avoid conflict with other tasks the variable could be scoped to the task. It would be very similar to a local variable in a function in a programming language.

Package level variables are probably the most common and allow you to define variables used throughout your app.

In summary, variables can be defined at many different scopes just because that functionality is already needed and "adding" scoping to things like tasks is really no additional effort. There may be cases where that is needed so it is nice to have the option. In my experience package and container scoped variables are the most common.