# mappedBy

## Purpose

The `mappedBy` static property adds the ability to change how a bidirectional associations is linked

## Examples

    class Airport {
       static mappedBy = [outgoingFlights:'departureAirport',
                          incomingFlights:'destinationAirport']
       static hasMany = [outgoingFlights:Route,
                         incomingFlights: Rout]
    }class Route {
        Airport departureAirport
        Airport destinationAirport
    }

In this example the `Airport` class defines two bidirectional one-to-many associations. Without defining `mappedBy` this is impossible as GORM cannot differentiate which of the two properties on the other end of the association (either `departureAirport` or `destinationAirport` in the `Route` class) each one-to-many should be associated one.

The solution is to define `mappedBy` which tells the `Airport` class how each association relates to the other side.