Creating a Synchronous Transformation with the Script Component

Artikkeli
12/03/2008

You use a transformation component in the data flow of an Integration Services package to modify and analyze data as it passes from source to destination. A transformation with synchronous outputs processes each input row as it passes through the component. A transformation with asynchronous outputs waits until it has received all input rows to complete its processing. This topic discusses a synchronous transformation. For information about asynchronous transformations, see Creating an Asynchronous Transformation with the Script Component. For more information about the difference between synchronous and asynchronous components, see Understanding Synchronous and Asynchronous Transformations.

For an overview of the Script component, see Extending the Data Flow with the Script Component.

The Script component and the infrastructure code that it generates for you simplify significantly the process of developing a custom data flow component. However, to understand how the Script component works, you may find it useful to read the steps involved in developing a custom data flow component in the section on Developing a Custom Data Flow Component, and especially Developing a Custom Transformation Component with Synchronous Outputs.

Getting Started with a Synchronous Transformation Component

When you add a Script component to the Data Flow pane of SSIS Designer, the Select Script Component Type dialog box opens and prompts you to select a Source, Destination, or Transformation component type. In this dialog box, select Transformation.

Configuring a Synchronous Transformation Component in Metadata-Design Mode

After you select the option to create a transformation component, you configure the component by using the Script Transformation Editor. For more information, see Configuring the Script Component in the Script Component Editor.

A data flow transformation component has one input, and supports one or more outputs. Configuring the input and outputs for the component is one of the steps that you must complete in metadata design mode, by using the Script Transformation Editor, before you write your custom script.

Configuring Input Columns

A transformation component has one input.

On the Input Columns page of the Script Transformation Editor, the column list shows the available columns from the output of the upstream component in the data flow. Select the columns that you want to transform or pass through. Mark any columns that you want to transform in place as Read/Write.

For more information about the Input Columns page of the Script Transformation Editor, see Script Transformation Editor (Input Columns Page).

Configuring Inputs, Outputs, and Output Columns

A transformation component supports one or more outputs.

On the Inputs and Outputs page of the Script Transformation Editor, you can see that a single output has been created, but the output has no columns. On this page of the editor, you may need or want to configure the following items.

Create one or more additional outputs, such as a simulated error output for rows that contain unexpected values. Use the Add Output and Remove Output buttons to manage the outputs of your synchronous transformation component. All input rows are directed to all available outputs unless you indicate that you intend to redirect each row to one output or the other. You indicate that you intend to redirect rows by specifying a non-zero integer value for the ExclusionGroup property on the outputs. The specific integer value entered in ExclusionGroup to identify the outputs is not significant, but you must use the same integer consistently for the specified group of outputs.

Note

You can also use a non-zero ExclusionGroup property value with a single output when you do not want to output all rows. However, in this case, , you must explicitly call the DirectRowTo<outputbuffer> method for each row that you want to send to the output.
Assign a more descriptive name to the input and outputs. The Script component uses these names to generate the typed accessor properties that you will use to refer to the input and outputs in your script.
Leave columns as is for synchronous transformations. Typically a synchronous transformation does not add columns to the data flow. Data is modified in place in the buffer, and the buffer is passed on to the next component in the data flow. If this is the case, you do not have to add and configure output columns explicitly on the transformation's outputs. The outputs appear in the editor without any explicitly defined columns.
Add new columns to simulated error outputs for row-level errors. Ordinarily multiple outputs in the same ExclusionGroup have the same set of output columns. However, if you are creating a simulated error output, you may want to add more columns to contain error information. For information about how the data flow engine processes error rows, see Using Error Outputs in a Data Flow Component. Note that in the Script component you must write your own code to fill the additional columns with appropriate error information. For more information, see Simulating an Error Output for the Script Component.

For more information about the Inputs and Outputs page of the Script Transformation Editor, see Script Transformation Editor (Inputs and Outputs Page).

Adding Variables

If you want to use existing variables in your script, you can add them in the ReadOnlyVariables and ReadWriteVariables property fields on the Script page of the Script Transformation Editor. To add multiple variables, separate the variable names by commas.

For general information about how to use variables with the Script component, see Using Variables in the Script Component.

For more information about the Script page of the Script Transformation Editor, see Script Transformation Editor (Script Page).

Scripting a Synchronous Transformation Component in Code-Design Mode

After you have configured the metadata for your component, open the Visual Studio for Applications (VSA) IDE and write your custom script by using the Visual Basic .NET language. You can open the VSA IDE from the Script page of the Script Transformation Editor by clicking Design Script.

For important information that applies to all kinds of components created by using the Script component, see Coding and Debugging the Script Component.

Understanding the Auto-generated Code

When you open the VSA IDE after you create and configuring a transformation component, the editable ScriptMain class appears in the code editor with a stub for the ProcessInputRow method. The ScriptMain class is where you will write your custom code, and ProcessInputRow is the most important method in a transformation component.

If you open the VSA Project Explorer window, you can see that the Script component has also generated read-only BufferWrapper and ComponentWrapper project items. The ScriptMain class inherits from the UserComponent class in the ComponentWrapper project item.

At run time, the data flow engine invokes the ProcessInput method in the UserComponent class, which overrides the ProcessInput method of the ScriptComponent parent class. The ProcessInput method in turn loops through the rows in the input buffer and calls the ProcessInputRow method one time for each row.

Writing Your Custom Code

A transformation component with synchronous outputs is the simplest of all data flow components to write. For example, the single-output example shown later in this topic consists of the following custom code:

    Row.City = UCase(Row.City)

To finish creating a custom synchronous transformation component, you use the overridden ProcessInputRow method to transform the data in each row of the input buffer. The data flow engine passes this buffer, when full, to the next component in the data flow.

Depending on your requirements, you may also want to write script in the PreExecute and PostExecute methods, available in the ScriptMain class, to perform preliminary or final processing.

Working with Multiple Outputs

Directing input rows to one of two or more possible outputs does not require much more custom code than the single-output scenario discussed earlier. For example, the two-output example shown later in this topic consists of the following custom code:

    Row.City = UCase(Row.City)
    If Row.City = "REDMOND" Then
        Row.DirectRowToMyRedmondAddresses()
    Else
        Row.DirectRowToMyOtherAddresses()
    End If

In this example, the Script component generates the DirectRowTo<OutputBufferX> methods for you, based on the names of the outputs that you configured. You can use similar code to direct error rows to a simulated error output.

Examples

The examples here demonstrate the custom code that is required in the ScriptMain class to create a synchronous transformation component.

Note

These examples use the Person.Address table in the AdventureWorks sample database and pass its first and fourth columns, the intAddressID and nvarchar(30)City columns, through the data flow. The same data is used in the source, transformation, and destination samples in this section. Additional prerequisites and assumptions are documented for each example.

Single Output Synchronous Transformation Example

This example demonstrates a synchronous transformation component with a single output. This transformation passes through the AddressID column and converts the City column to uppercase.

If you want to run this sample code, you must configure the package and the component as follows:

Add a new Script component to the Data Flow designer surface and configure it as a transformation.
Connect the output of a source or of another transformation to the new transformation component in SSIS Designer. This output should provide data from the Person.Address table of the AdventureWorks sample database that contains the AddressID and City columns.
Open the Script Transformation Editor. On the Input Columns page, select the AddressID and City columns. Mark the City column as Read/Write.
On the Inputs and Outputs page, rename the input and output with more descriptive names, such as MyAddressInput and MyAddressOutput. Notice that the SynchronousInputID of the output corresponds to the ID of the input. Therefore you do not have to add and configure output columns.
On the Script page, click Design Script and enter the script that follows. Then close the script development environment and the Script Transformation Editor.
Create and configure a destination component that expects the AddressID and City columns, such as a SQL Server destination, or the sample destination component demonstrated in Creating a Destination with the Script Component. Then connect the output of the transformation to the destination component. You can create a destination table by running the following Transact-SQL command in the AdventureWorks database:
```
CREATE TABLE [Person].[Address2](
    [AddressID] [int] NOT NULL,
    [City] [nvarchar](30) NOT NULL
)
```
Run the sample.

Public Class ScriptMain
    Inherits UserComponent

    Public Overrides Sub MyAddressInput_ProcessInputRow(ByVal Row As MyAddressInputBuffer)

        Row.City = UCase(Row.City)

    End Sub

End Class

Two-Output Synchronous Transformation Example

This example demonstrates a synchronous transformation component with two outputs. This transformation passes through the AddressID column and converts the City column to uppercase. If the city name is Redmond, it directs the row to one output; it directs all other rows to another output.