Hands-On Microsoft SQL Server 2008 Integration Services part 13 pot

98 Hands-On Microsoft SQL Server 2008 Integration Services System task and will see that the variable value is used by the task to create the required folder. 10. Delete the newly created folder FSTdirectory form the C:\SSIS folder and the connection manager from BIDS by simply selecting it and pressing . Click Yes on the pop-up dialog box to confirm deletion of the connection manager. 11. Right-click anywhere on the blank surface of the Control Flow Panel and choose Variables from the context menu. This will open the Variables window. Add a variable by clicking the Add Variable button, which is the leftmost button on the menu bar in the Variables window. In the Name column, type directory and change the Data Type to String. In the Value field, type C:\ SSIS\ FSTdirectory, as shown in the Figure 3-8. 12. Double-click the File System task to open the Task Editor. In the IsSourcePathVariable field’s drop-down list, select True. Note that this converts the SourceConnection field to a SourceVariable field. 13. Click in the SourceVariable field and select the User::directory variable from the list of variables. Click OK to close the File System Task Editor as shown in Figure 3-9. 14. Press 5 to execute the package. The File System task turns green and the Output window shows the Success message. 15. Press -5 to stop debugging the package, or choose Debug | Stop Debugging. Switch to Windows Explorer to see that the folder has been created. 16. In BIDS, choose File | Save All and leave the project open, as you will return to this project later in the chapter. Review You have created a user-defined variable and used its value to populate the SourceVariable field in the File System Task Editor. Because you specified the IsSourcePathVariable as True, so when you run this package, the File System task knows that it has to read the value of the SourceVariable field from the User::directory variable. Though you have defined a static value to the variable, this is a good example of how a variable can affect the task. In real-life scenarios, the variables are populated either by package configurations or by the upstream tasks in the package at run time and the downstream tasks use those variables to get dynamically updated values. Figure 3-8 Adding a variable to the package Chapter 3: Nuts and Bolts of the SSIS Workflow 99 Precedence Constraints While creating the workflow and linking tasks, you can decide the conditions that can affect the running of successive tasks. To do this, you use precedence constraints when linking two or more executables. Within the SSIS world, an executable is defined as a container, a task, or an event handler. The executable for which you define the precedence constraint to be applied after it has run is called the precedence executable, and the executable for which you define a precedence constraint to be applied before it could run is called the constrained executable. The precedence constraints can be affected by the execution result of the precedence executable. For example, you may wish to stop Figure 3-9 Configuring the File System Task Editor to get a value from a user-defined variable 100 Hands-On Microsoft SQL Server 2008 Integration Services the constrained executable from running if the precedence executable fails to complete. The precedence constraints created in a package can also be seen in the Package Explorer tab in BIDS. When you connect two tasks on the Control Flow Panel by dragging the green arrow from a task on to the other task, you actually use a precedence constraint. You can open the Precedence Constraint Editor by double-clicking the green and can specify various options for configuring the constraints. The Editor window is divided into two parts: Constraint Options and Multiple Constraints. Constraint Options The precedence constraint can be based on a combination of the execution results and the evaluation of the expressions. In the Constraint Options section, you can select the execution result and provide an expression to be evaluated. Evaluation Operation c is defines the EvalOp property of the constraint. You have four choices here that you can see when you click the down arrow button. e selection of the option here determines the way the precedence constraint combines execution results and evaluation expressions to determine whether to run the constrained executable. Constraint c Use only the execution result from the precedence executable to determine whether the constrained executable runs. Expression c Use only the Expression property to determine whether the constrained executable runs. When selected, the Expression field becomes available to enable you to define an expression, which must be a valid SSIS expression. Expression And Constraint c Combines the requirements of both the Constraint and the Expression. Expression Or Constraint c Uses either of the two options to decide the execution of the constrained executable. Value c is field refers to the value property of the precedence constraint and specifies the value of the execution result of the precedence executable to determine whether to run the constrained executable. You have three options available here: Completion c e constrained executable will run on the completion of the precedence executable with no regard to the outcome—that is, success or failure. For example, you may want to run a consistency check on your database toward the end of your nightly update operation without regard to whether the data uploading task successfully loaded data or failed to load any data. Chapter 3: Nuts and Bolts of the SSIS Workflow 101 Success c e constrained executable will run only when the precedence executable has completed successfully or has a result of “No Errors Occurred” from the preceding task. e No Errors Occurred result is returned by a disabled task in the control flow to let the work flow continue. Failure c e constrained executable will run only when the precedence executable has failed. For example, you may want to alter the data flow when the data loading task fails. Expression c In this field, you can specify an expression that evaluates to Boolean true to run the constrained executable. is Expression field becomes available only when you choose the Expression and Constraint or Expression Or Constraint option in the Evaluation Operation field. e expression can include functions, operators, and system and custom variables. You can click Test to evaluate the expression or test whether the expression you have specified is syntactically correct. A simple expression is shown in Figure 3-10. Figure 3-10 The Precedence Constraint Editor 102 Hands-On Microsoft SQL Server 2008 Integration Services Multiple Constraints A constrained executable can have multiple constraints—that is, more than one precedence executable may apply precedence constraints on a constrained executable. In situations for which you have multiple constraints on a constrained executable, you can specify the criteria for multiple constraints to control the execution of the constrained executable in the Multiple Constraints section. You can choose one of the two mutually exclusive options—Logical AND or Logical OR. Selecting Logical AND sets the LogicalAnd property of the precedence constraints to True and implies that all the constraints must evaluate to True before running the constrained executable. Selecting Logical OR sets the LogicalAnd property to False and implies that one of the constraints must evaluate to True to run the constrained executable. The precedence constraint behavior is covered in a Hands-On exercise in Chapter 5, where you will be able to see how the constrained executables are affected by your choice of a particular constraint. Integration Services Expressions Integration Services allows you to set task values dynamically using variables that are updated at run time by other tasks. This facility is quite powerful and great in many respects; however, it does not solve all the real-life problems associated with population of configuration values. Developers must often evaluate a value for a task based on a value generated by another task. This requires that they write a custom piece of code to evaluate the required value, as the value generated by the first task can’t be directly used in the second task. For example, if you want to create a folder in which the update files you receive daily are kept, and you want to add a date part in the name of the folder, you must evaluate the folder name using the two values: one for the static part and one for the dynamic date part. This is where Integration Services shows its real power. SSIS allows you to evaluate a value using expressions. SSIS tasks expose some of their properties that can be dynamically updated using expressions. Expressions can be used for the following purposes: Variables and property expressions can use expressions to update values at run time. c Integration Services has a For Loop Container, which you will study in the next c chapter that uses expressions for the looping criteria. As you’ve seen earlier in the chapter, precedence constraints use expressions to c evaluate a condition. Data flow transformations such as the Conditional Split Transformation and the c Derived Column Transformation have an Expression Builder interface. Chapter 3: Nuts and Bolts of the SSIS Workflow 103 Integration Services expressions consist of one or more variables, columns, functions, and operators. You can use all these together to build an expression to evaluate the required value. The language of the Integration Services expressions uses syntax similar to that used in C and C#. The Expression syntax contains identifiers, literals, operators, and functions. The collection of syntax, data type conversion rules, truncation rules, and string padding is called the Expression grammar. SSIS provides GUI tools to help you build expressions. The Expression Builder is present in most of the Control Flow tasks in the Expressions page to help you apply expressions to properties of the tasks. The expressions you apply to properties are called Property Expressions. Figure 3-11 shows the example of property expression for the File System task that you used in the last Hands-On exercise. If you open the package again and open Expression Builder via the Expressions page and build the expression shown (as explained in the next paragraph), you can then click Evaluate Expression to evaluate this expression at design time. In the Expression Builder, you can type information into the Expression box and drag and drop any of the items from the top two panes to the Expression box to build Figure 3-11 Expression Builder user interface 104 Hands-On Microsoft SQL Server 2008 Integration Services your expression. In the top-left pane of this dialog box, you can drag and drop any of the system- or user-defined variables. When you drop variables in the Expression box, the required syntax elements such as the @ prefix are automatically added to the variable names. You can also select columns from this pane if they are applicable to the task and are available there. And from the pane on the right, you can choose from various functions and operators. Figure 3-11 also shows a sample expression, which was built using literals, concatenate operator (+) from the operators, system- and user- defined variables, and a type cast to convert the date type to string. You can evaluate your expression at design time by clicking Evaluate Expression and the result will be shown in the Evaluated Value field. This will not include any values that are not available at design time. Understand that some of the variables will be populated at run time and they will have no value at design time; hence the evaluation may not give you the exact result that will be created at run time. This evaluation of an expression is accomplished by the Expression Evaluator, which also determines whether expressions adhere to the rules of Expression grammar. As mentioned, property expressions can be applied to any of the exposed properties in Control Flow tasks and to some of the data flow components, as not all data flow components support property expressions. The data flow components that support property expressions expose their properties on the parent data flow task. You can find functions and operators listed in the top-right pane of the Expression Builder. Integration Services Expression language has a rich set of syntax rules and functions that cannot be covered in detail in this book. However, detailed explanations for the expressions used will be provided wherever applicable. Refer to Microsoft SQL Server 2008 Books Online for more details on expressions. Following is the brief discussion of these functions and operators. Mathematical Functions c When you expand this folder, you will see 11 functions, such as ABS, LOG, SQUARE, and SQRT. ese functions perform calculations based on numeric input values provided as parameters to the functions and return numeric values. String Functions c is folder contains 14 string functions, such as LEN, LOWER, LTRIM, RIGHT, and SUBSTRING. String functions perform specified operations on string or hexadecimal input values and return a string or numeric value. Date/Time Functions c Eight Date/Time functions here, such as DATEADD, GETDATE, and MONTH, perform operations on date and time values and can return string, numeric, or date and time values. NULL Functions c irty functions, such as ISNULL and NULL, are available for particular data types. ISNULL returns a Boolean result based on whether an expression is null, whereas NULL returns a null value of a requested data type. Chapter 3: Nuts and Bolts of the SSIS Workflow 105 Type Casts c ese twenty-nine functions help you perform data type conversions for a variable, a column, or an expression from one data type to another, such as string to integer or date/time to string. Operators c About twenty-two operators, such as (+) add, (+) concatenate, (/) divide, and (>) greater than. You will be using property expressions in various Hands-On exercises throughout this book, but just to tickle your brain, the following is a simple exercise using property expressions. Hands-On: Using Expressions to Update Properties at Run Time You need to create a directory to keep the update files you receive daily. But this time, you want to keep the daily update files in their own folder—you need to create a folder each night and want to include a date part in the name of the folder. Method You can do this in at least two ways. You can write an expression on the variable’s value property to evaluate the new value and pass that value to the SourceConnection field. Or you can go back to the first part of the last Hands-On exercise, in which you used a connection manager for the SourceConnection field and provided a static value of C:\SSIS\FSTdirectory. As part of the second method, you can add property expression on the FSTdirectory Connection Manager to generate a connection string at run time. You will be using the second method in this exercise so that you can have an introduction to the Expression Builder. Exercise (Configuring the File System Task with Hard-Coded Values) The first part of this exercise is to open the Creating Directory project and change the settings to go back to a hard-coded value for the SourceConnection field. 1. Open the Creating Directory project with BIDS if it is not already open. 2. Double-click the File System Task to open the editor. 3. Click in the IsSourcePathVariable field and change the value to False. 4. Click in the SourceConnection field and choose <New connection…> from the drop-down list. Choose Create Folder in the Usage Type field of the File Connection Manager Editor. Type SSISdirectory in the Folder field. You don’t need to provide a path here, as that will be evaluated at run time using the expression you are going to build. Click OK twice to close the File System Task Editor. 106 Hands-On Microsoft SQL Server 2008 Integration Services Exercise (Using Property Expressions to Evaluate ConnectionString at Run Time) In this part, you will build a property expression on the ConnectionString property of the FSTdirectory Connection Manager to evaluate the directory name, similar to C:\ SSIS\FSTdirectory20091014, having the date attached as a suffix to the folder name. 5. In the Connection Manager area, right-click the FSTdirectory Connection Manager and choose Properties from the context menu. 6. In the Properties window, click in the Expressions field and then click the ellipsis button. This will open the Property Expressions Editor. 7. Click in the Property column and choose ConnectionString Property from the drop-down list. Click the ellipsis button shown on the right to open the Expression Builder. 8. In the top left pane of Expression Builder, expand Variables and drag and drop the User::directory variable in the Expression area. Then do the following in sequence: c Expand Operators and add the concatenate (+) operator. c Expand Type Casts and add (DT_WSTR, <<length>>); then change <<length>> to 4 to make it (DT_WSTR, 4). c Expand Date/Time Functions and add YEAR( <<date>> ); then drop the GETDATE() function on the <<date>> part of the YEAR( <<date>> ) function. Your expression should look like this: @[User::directory] + (DT_WSTR, 4) YEAR( GETDATE() ) 9. Click Evaluate Expression, and you will see a value of current year attached to the User::directory variable (which in my case is C:\ SSIS\FSTdirectory2009 at this point in time). Complete the expression by adding the following so that the complete expression looks like one shown in Figure 3-12: RIGHT("0" + (DT_WSTR, 2) MONTH( GETDATE() ), 2) + RIGHT("0" + (DT_WSTR, 2) DAY( GETDATE() ), 2) 10. Click OK twice to return to the Properties window. If you expand the Expressions field, you should see the expression you developed earlier. 11. Press 5 on the keyboard to execute the package. When the File System task has turned green, press - 5 to stop debugging and go back to design mode. Choose File | Save All and then close the project. 12. Using Windows Explorer, check to see that the required folder has been created. Chapter 3: Nuts and Bolts of the SSIS Workflow 107 Review You’ve learned one of the core skills that will help you create packages that can update themselves using the current values at run time. You’ve used Expression Builder to write an expression. You understand that this can also be written directly without using Expression Builder’s drag and drop feature to speed things up, but Expression Builder helps in providing quick syntax help. Summary This chapter covered the basic components used for building a workflow in an SSIS package. Integration Services provides connection managers that help various tasks in the package to establish connections to the external data stores. Variables provided in SSIS are different from those in DTS 2000; they can have scope and are categorized as system variables that are read-only which you cannot create and modify, or as the user-defined variables that you create to meet the needs of the package. Precedence Figure 3-12 Building a property expression . System Task Editor. 106 Hands-On Microsoft SQL Server 2008 Integration Services Exercise (Using Property Expressions to Evaluate ConnectionString at Run Time) In this part, you will build a property. File System Task Editor to get a value from a user-defined variable 100 Hands-On Microsoft SQL Server 2008 Integration Services the constrained executable from running if the precedence executable. shown in Figure 3-10. Figure 3-10 The Precedence Constraint Editor 102 Hands-On Microsoft SQL Server 2008 Integration Services Multiple Constraints A constrained executable can have multiple