Last updated: 2020-02-28

CustomSelect / CustomCols

The customselect feature allows you to control what rows & columns get synchronized from one database to another. This functionality works both on the fly (when CRUD invokes a trigger), and when doing a fullcopy.

The command takes a SELECT statement, and is helpful in the following scenarios:

  • Tables differ in structure and/or field names between the source and destination databases
  • You want to join different tables from the source, into a single table in the destination
  • You want to apply a filter on what actually gets synchronized (by adding a WHERE clause)
  • Any combination of the above!

The test file t/20-postgres.t has a working example (grep for ‘customcols’).

Example Usage

The basic idea is to replace the default SELECT * FROM table with a modified select list, by calling:

bucardo add customcols mytable "SELECT a,b, foo AS bar"

You can optionally constrain to a certain sync:

bucardo add customcols mytable "SELECT a,b, foo AS bar" sync=mysync

And/or to a certain database (which is probably what you want to do here):

bucardo add customcols mytable "SELECT a,b, foo AS bar" db=mymongodb


  1. You can’t sync from a view, you can only sync from tables
  2. The same view definition can be adapted to become the “customcols” query

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