Grails / GORM: difference between lazy: false & fetchMode impatience

Question

In Grails / GORM, what is the difference between static mapping = {xyz lazy: false} and static fetchMode = [xyz: 'eager'] ?

Example:

 class Book { static belongsTo = [author: Author] static mapping = {author lazy: false} static fetchMode = [author: 'eager'] } 

Answer 1

Difference between lazy: false and fetchMode 'eager'

• lazy: false will get the linked domain object, querying the database again with Select Query, but the fetchMode 'eager' that is deprecated now (use fetch: 'join') will try to join the linked tables (using an external join) and select the related objects in one request.
• lazy: false will have another database query to retrieve the associated domain object and, therefore, will have more interaction with the database, while fetching “join” will have less interaction to retrieve the same data.
• FetchMode Join overrides the lazy property. This will simply ignore the lazy: false.

If you are interested in a detailed explanation about Fetchmodes, see http://www.solidsyntax.be/2013/10/17/fetching-collections-hibernate/ . This article describes the Hibernate fibmate models and the output that they produce.

Hope this helps.