6 Groovy Preconditions

General format

This is general format of a Groovy-based precondition:

databaseChangeLog = {
   changeSet(author: '...', id: '...') {
      preConditions {
         grailsPrecondition {
            check {
               // use an assertion
               assert x == x
               // use an assertion with an error message
               assert y == y : 'value cannot be 237'
               // call the fail method
               if (x != x) {
                  fail 'x != x'
               }
               // throw an exception (the fail method is preferred)
               if (y != y) {
                  throw new RuntimeException('y != y')
               }
            }
         }
      }
   }
}

As you can see there are a few ways to indicate that a precondition wasn't met:

• use a simple assertion
• use an assertion with a message
• call the fail(String message) method (throws a PreconditionFailedException)
• throw an exception (shouldn't be necessary - use assert or fail() instead)

Available variables

• database
• the current Liquibase Database instance
• databaseConnection
• the current Liquibase DatabaseConnection instance, which is a wrapper around the JDBC Connection (but doesn't implement the Connection interface)
• connection
• the real JDBC Connection instance (a shortcut for database.connection.wrappedConnection)
• sql
• a groovy.sql.Sql instance which uses the current connection and can be used for arbitrary queries and updates
• resourceAccessor
• the current Liquibase ResourceAccessor instance
• ctx
• the Spring ApplicationContext
• application
• the GrailsApplication
• changeSet
• the current Liquibase ChangeSet instance
• changeLog
• the current Liquibase DatabaseChangeLog instance

Utility methods

• createDatabaseSnapshotGenerator()
• retrieves the DatabaseSnapshotGenerator for the current Database
• createDatabaseSnapshot(String schemaName = null)
• creates a DatabaseSnapshot for the current Database (and schema if specified)