Overriding the default settings

A transformation can be defined that overrides the topic, partition and message key settings defined in the General tab.

To define a transformation:

1. Open the task you defined.
2. If you are defining a transformation for a single table, select one of the source tables. Otherwise, skip to Step 3.

3. Define a transformation that adds one of the following columns:

   Information note

   The columns listed below (prefixed with a $) instruct Replicate to route the message to the desired topic and/or partition, and will not be included in the actual message itself.

   • $topic - To write messages to a specific topic.
   • $partition - To write messages to a specific partition.
   • $key - To create a custom message key.

   For information on creating a transformation for a single table, see Defining transformations for a single table/view.

   For information on creating a global transformation rule, see Starting the Global Transformation Rules wizard.

4. Define an expression for the new column that returns the following values:
   • For a $topic column, the expression should return the topic name.
   • For a $partition column, the expression should return the partition number. Note that an error will be returned during runtime if the partition number does not exist.
   • For a $key column, the expression should return the message key contents. Note that the expression must return a non-empty value.

   For information on creating expressions, see Using the Expression Builder.