Question

I am getting to know SSIS, I apologize if the question is too simple.

I got a set of tasks inside a foreach-loop-container.
The first task needs only to get executed on condition that a certain user variable is not null or empty.
Otherwise, the flow should skip the first task and continue to the second one.

How would I go about realizing this (in detail) ?

Answer 1

Issue 1: There are two ways to interpret your logic: “…a certain user variable is not null or empty”:

1. The (Variable is Not Null) OR the (Variable is Empty).

2. The (Variable is Not Null) OR the (Variable is Not Empty).

   It’s all about the object(s?) of the word “not”. The differences are subtle but will impact when the first task in the Foreach loop executes. For demonstration purposes, I am assuming you intend #1.

   Issue 2: The first task can no longer be first. In order to accomplish what you desire using SSIS inside the BIDS environment, you need to place another task ahead of the task formerly known as “the first task”. This is so you can set a Precedence Constraint on the former first task from the new first task.
   It is possible to accomplish what you desire by designing your SSIS dynamically from managed code, but I don’t think this issue warrants the overhead associated with that design choice.
   I like using an empty Sequence Container as an “Anchor” task – a task that exists solely to serve as the starting endpoint of a Precedence Constraint. I heavily document them as such. I don’t want anyone deleting the “unnecessary empty container” and roaming the halls for days shaking their heads and repeating “Andy, Andy, Andy…” but I digress.

   In the example below, I have two precedence constraints leaving the empty Sequence Container. One goes to the task that may be skipped and the other to the task following the task that can sometimes be skipped. A third precedence constraint is required between the task that can sometimes be skipped and the task following. It is important to note this third precedence constraint must be edited and the Multiple Constraints option set to OR. This allows the task following to execute when either of the mutually exclusive previous paths are taken. By default, this is set to AND and will require both paths to execute. By definition, that will not – cannot – happen with mutually exclusive paths.

   I test the value of an SSIS String variable named @MyVar to see if it’s Null or Empty. I used the Expression Only Evaluation Option for the constraints leaving the empty Sequence Container. The expressions vary but establish the mutual exclusivity of the expression. My Foreach Loop Container looks like this:

I hope this helps.

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