Wednesday, June 22, 2011

SQL Bulk Copy

In an earlier post I talked about a generic SSIS package for staging data using SQL Bulk Copy. I have been using it extensively without fail . . . until just recently.

I got a new set of files from a new business unit that we were bringing into our data warehouse solution. Of their 20 files 14 loaded without issue and the remaining 6 failed with an error similar to the one below.

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The given value of type String from the data source cannot be converted to type int of the specified target column.

I kept going back to the developers that created the extract process and telling them that they were doing something wrong with their encoding or delimiters but neither us nor them could actually find the issue. Until now.

Turns out the issue is related to SQL Bulk Copy, numeric columns, and null values. Apparently SQL Bulk Copy does not, by default, keep nulls. Instead, it converts them to empty strings. Well, as I'm sure you know, SQL Server doesn't like it when you try to load empty strings, or any strings for that matter, into a numerically typed column.

There are a couple of solutions.

  1. Make sure to replace all nulls with zeros when created flat files with numeric data that will be consumed by BCP.
  2. Use the KeepNulls option when executing BCP. In my SSIS solution I changed my SqlBulkCopy object creation to look like this . . .
Dim bc As SqlBulkCopy = New SqlBulkCopy(dbConn, SqlBulkCopyOptions.KeepNulls, bulkCopyTransaction)

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