Allow gradle plugin to create multiple migrate tasks for different (database) schemas

[aldas]

Currently "FlywayMigrateTask" depends on hard coded "project.flyway" property and it is really difficult to use gradle plugin when you need to migrate multiple different database instance schemas.

a la requirement: gradle build should be able to migrate 2 different (database instance) schemas before application/tests are run

task flywayMigrateA(type: org.flywaydb.gradle.task.FlywayMigrateTask) {
    extension = new org.flywaydb.gradle.FlywayExtension()
    extension.driver = "oracle.jdbc.OracleDriver"
    extension.schemas = ['DB1_SCHEMA_A']
    extension.locations = ['filesystem:database/A/']
    extension.sqlMigrationPrefix = "V"
    extension.initOnMigrate = true
    extension.outOfOrder = true
    extension.url = $databaseA_jdbc_connection_string
}

task flywayMigrateB(type: org.flywaydb.gradle.task.FlywayMigrateTask) {
    extension = new org.flywaydb.gradle.FlywayExtension()
    extension.driver = "oracle.jdbc.OracleDriver"
    extension.schemas = ['DB2_SCHEMA_B']
    extension.locations = ['filesystem:database/B/']
    extension.sqlMigrationPrefix = "V"
    extension.initOnMigrate = true
    extension.outOfOrder = true
    extension.url = $databaseB_jdbc_connection_string
}

so you could ./gradlew flywayMigrateA flywayMigrateB

It is curretly not possible so I changed org.flywaydb.gradle.task.AbstractFlywayTask extension property from private to protected.

private FlywayExtension extension

to

protected FlywayExtension extension

Now you'll be able to override extension from your custom tasks. There is probably nicer ways to to this but I'm not that good at Gradle/Groovy and this seems simple small change.

p.s. maybe it would be also good addition to change "prop" method from private to protected so if you need your own logic to get properties you do not need to reimplement almost all AbstractFlywayTask class as "createFlyway" method does not see your extended class prop method.

[axelfontaine]

Thanks for issue and the pull request! Looks like an easy improvement. Merged into 3.1 due out before the end of this month.

Cheers
Axel