Database Reference
In-Depth Information
Despite its minor shortcomings, the SSIS expression language remains an integral
part of the product, and as you'll see later in this chapter, it has some very practical
uses in a well-designed ETL ecosystem.
Putting
the
Expression
Language
to
Work
Now that you understand what the expression language is (and is not), let's talk about
some design patterns where you might use it.
Package Expressions
Although not as common as other uses, it is possible to use SSIS expressions to config-
ure package-level properties. Here are a handful of properties that may be set at the
package level by using expressions:
•
Disable
•
DisableEventHandlers
•
CheckpointFileName
•
MaxConcurrentExecutables
•
DelayValidation
•
Description
Consider the example of
MaxConcurrentExecutables
, which defines how
many executables (packages, tasks, etc.) can run concurrently. By setting this property
through an expression, the ETL developer would be able to dynamically control this
value based on any criteria visible through an expression.
Although these properties are configurable by using expressions, it's far more com-
mon to find package-level options set by using package parameters (with later versions
of SSIS) or package configurations (SQL Server 2008 and earlier). It is usually best to
share common values across package ancestries using parameters or configurations,
which allow you greater flexibility and easier maintenance. I expose this particular
design pattern more for the purpose of identifying it as an antipattern than for defining
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