Continuing a Loop After an Error

A common question on the SSIS forums is how to continue a loop after an error occurs. For example, you might have a For Each Loop container that iterates through a set of files in a folder. If one file is invalid, you want to continue processing the remaining files. Fortunately, there is a simple pattern that allows this to be accomplished.

I created a package to illustrate this. Basically, the package implements the scenario above. It consists of a For Each Loop to iterate through all the files in a folder. There is a data flow task that processes each input file, and runs it through a row count (just for illustration purposes). The Script task is there to illustrate an error handling task could be attached to the data flow, but it’s empty in the example package. It would need to be replaced with the appropriate task to handle a failure, such as a File System task to move the file to another folder.


The key to handling the errors is the Sequence container, or more specifically, how the Sequence container is set up. The OnError event handler for the Sequence container has been enabled. You can do this by selecting the Sequence container, then clicking the Event Handlers tab. Select the OnError event in the drop down, then click the link in the designer to create an empty event handler. It’s not necessary to add anything to event handler.


Once it has been created, go to the Variables window, and select the option to show System variables. Select the Propagate variable, and set the value to FALSE. This prevents any errors occurring on tasks inside the Sequence container from being raised to the For Each loop.


This is all that really needs to be done, but if you run the package with only this set, you’ll notice that the Data Flow task and the Sequence container both report an error. To prevent the Sequence Container from reporting an error, set the MaximumErrorCount property of the container to 0.


Note that you do not have to use a sequence container to accomplish this. You could make the same settings on individual tasks inside the For Each loop. However, the Sequence container gives you a common place to make the settings, and you can have as many tasks inside it as you’d like.

The example package is posted on my Skydrive. The zip file contains a folder call Import. The package expects this folder to be located in C:Temp. It contains 4 text files for the package to process. The 2nd file contains an error (one of the rows has fewer columns than it is supposed to), so that you can see the error behavior.

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