Tag: second level cahce

Recently we were hunting a strange bug. Take the following domain model:

class Computer {
  Coder coder
}

class Coder {
  static hasMany = [projects:Project]
}

Querying the computer and iterating over the respective coder and projects sometimes resulted in strange number of projects: 1. Looking into the underlying database we quickly found out that the number of 1 was not correct. It got even more strange: getting the coder in question via Coder.get in the loop yielded the correct results. What was the problem?
After some code reading and debugging another query which was called after the first one but before accessing the coder in the loop gave some insight:

  Coder.withCriteria {
    projects {
      idEq(projectId)
    }
  }

This second query also queried the Coder but constrained the projects to a specific one. These coders were populated into the second level cache and when we called computer.coder the second level cache returned the before queried coder. But this coder had only one project!
Since we only needed the number of coders with this project we changed the second
query to using count, so no instances of Coder are returned and thus saved in the second level cache. Bug fixed.