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

Review You have created a user-defined variable and used its value to populate the SourceVariable field in the File System Task Editor.. Value c This field refers to the value property o

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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 delete 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 f5 to execute the package The File System task turns green and the Output window shows the Success message

15. Press shift-f5 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

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

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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

have four choices here that you can see when you click the down arrow button The 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

determine whether the constrained executable runs

Expression

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

Constraint and the Expression

Expression Or Constraint

execution of the constrained executable

Value

c This 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

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

executable has completed successfully or has a result of “No Errors Occurred”

from the preceding task The No Errors Occurred result is returned by a

disabled task in the control flow to let the work flow continue

Failure

c The 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 This Expression field becomes

available only when you choose the Expression and Constraint or Expression

Or Constraint option in the Evaluation Operation field The 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

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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

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

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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

such as ABS, LOG, SQUARE, and SQRT These functions perform calculations based on numeric input values provided as parameters to the functions and return numeric values

String Functions

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

GETDATE, and MONTH, perform operations on date and time values and can return string, numeric, or date and time values

NULL Functions

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

Type Casts

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

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

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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 f5 on the keyboard to execute the package When the File System task has turned green, press shift-f5 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

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