SQL Server Integration Services Task Objects
SSIS tasks are the foundation of the Control Flow in SSIS. When you are on the Control Flow design surface in SSDT, the SSIS Toolbox is populated with a set of task components that can be connected together to represent a workflow for your package. You’ll also learn later in Chapter 18 how tasks can also react to failures in the package in the Event Handler tab.
A task is a discrete unit of work that can perform typical actions required by an ETL process, from moving a file and preparing data sources to sending email confirmations when everything is complete. This is most evident in the fact that the Data Flow is tied to the Control Flow with a specific Data Flow Task. More advanced tasks enable you to perform actions like executing SQL commands, sending mail, running VB or C# code, and accessing web services. The SSIS Toolbox contains a large list of out-of-the-box tasks that you can use for ETL package development. Most of the tasks are covered in this chapter, with some in less detail because they are covered in other chapters. Two exceptions are the Looping and Sequence Containers, which are covered separately in Chapter 6. This chapter introduces you to most of the tasks you’ll be using on a frequent basis and provides some examples that demonstrate how to use them. This material is reinforced as you read through the rest of the tutorial, because each of these tasks is used in at least one further example in subsequent chapters.
SSIS TASK OBJECTS
Tasks are component-based, small units of work that can be sequenced in an SSIS package Control Flow or in the Event Handlers tab. To add a task to a package, click and drag it from the SSIS Toolbox onto the design surface. If you don’t see the SSIS Toolbox, you can open it by clicking SSIS Toolbox under the SSIS menu in SSDT. Once you drag the task over, you can then double-click the task’s icon in the design pane to configure it. You may immediately see a red or yellow warning on the task until you configure any required properties. Setup requirements vary depending upon the task. You may also need to provide a database connection, external mail server connection, or the name of an external package to complete the task’s configuration.
Using the Task Editor
To configure a task you need to access the Task Editor. To do so, double-click directly on the task’s icon in the Control Flow design surface or right-click the task and select the Edit option in the pop-up menu. In either case, generally you’ll see a Task Editor dialog appear (generally, because not all tasks have a Task Editor to configure). The Task Editor provides a specialized interface that enables configuration of the task’s properties. Each task has different property and setup requirements, but the Task Editor always employs a consistent design that makes it easy to follow. Below diagram shows an example of a typical Task Editor dialog to help get you oriented.
Each Task Editor contains a few generic properties such as its Name and Description. Try to select a meaningful name that best represents what the task is doing. Otherwise, your error log will be tough to read later. Each tab of the Task Editor varies according to what you select in the previous tab. Familiarizing yourself with this dialog will make configuring new tasks much easier.
The Task Editor Expressions Tab
SSIS uses a concept of setting the value of most task properties to a dynamic expression that is evaluated at runtime. This way, you can dynamically configure packages at runtime, replacing the Dynamic Properties Task and scripting-based configuration of the legacy DTS object model. Common to all the tasks is an Expressions tab in each of the editors that exposes the properties you can set dynamically at runtime with an expression. The expression can be a constant value, an expression, or an SSIS variable that is either a scalar constant or an expression. With this capability, you could read a series of variables from a configuration file (these are discussed later) and then dynamically set properties of any SSIS task. We provide many examples of using expressions throughout this tutorial. Chapter 5 is dedicated to variables and expressions, and explains how to use them in SSIS.
For a basic understanding of the Expressions tab within each task, click the ellipsis (…) button next to the Expressions option in the Expressions tab of any of the Task Editors. This will take you to the Property Expressions Editor, where you can set properties within a task — either directly by providing the actual expression or indirectly by providing the variable that evaluates to the result of an expression. To create a new one, select the property you wish to set from the Property column and then type the expression into the Expression column. Optionally, you can also select the ellipsis button in the Expression column to open Expression Builder, where you can create an expression using a visual UI. You’ll see this capability in most of the SSIS tasks.
LOOPING AND SEQUENCE TASKS
First up in the SSIS Toolbox are three container tasks: For Loop, Foreach, and Sequence. These are all Control Flow Tasks that simplify the process of repeated processing of a set of logic. In legacy DTS, looping constructs were not intuitive. If you wanted this type of Control Flow logic, you had to set properties on the tasks directly using code in the ActiveX Scripting Tasks. To achieve the same thing in SSIS, you only need to add one of these containers to your Control Flow and define what is being used to enumerate the loop. Again, these containers are covered in detail in Chapter 6, so they are only briefly covered here.