db4o update behavior is regulated by Update Depth. Understanding update depth will help you to improve performance and avoid unnecessary memory usage. A common pitfall is that the update-depth is to small and that the objects are not updated. In such cases you either need to explicitly store the related objects individually or increase the update-depth.
For example in this code we add a new friend and store the object. Since a collection is also handled like a regular object, it is affected by the update-depth. In this example we only store the person-object, but not the friend-collection-object. Therefore with the default-update depth of one the update isn't store. In order to update this properly, you either need to set the update depth to two or store the friend-list explicitly.
using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile)) { Person jodie = QueryForJodie(container); jodie.Add(new Person("Jamie")); // Remember that a collection is also a regular object // so with the default-update depth of one, only the changes // on the person-object are stored, but not the changes on // the friend-list. container.Store(jodie); } using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile)) { Person jodie = QueryForJodie(container); foreach (Person person in jodie.Friends) { // the added friend is gone, because the update-depth is to low Console.WriteLine("Friend=" + person.Name); } }
Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile) Dim jodie As Person = QueryForJodie(container) jodie.Add(New Person("Jamie")) ' Remember that a collection is also a regular object ' so with the default-update depth of one, only the changes ' on the person-object are stored, but not the changes on ' the friend-list. container.Store(jodie) End Using Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile) Dim jodie As Person = QueryForJodie(container) For Each person As Person In jodie.Friends ' the added friend is gone, because the update-depth is to low Console.WriteLine("Friend=" & person.Name) Next End Using
So for this example setting the update-depth to two will fix the issue. For lots of operation a update-depth of two is pretty reasonable. This allows you to update collections without storing them explicitly.
IEmbeddedConfiguration config = Db4oEmbedded.NewConfiguration(); config.Common.UpdateDepth = 2; using (IObjectContainer container = Db4oEmbedded.OpenFile(DatabaseFile)) {
Dim config As IEmbeddedConfiguration = Db4oEmbedded.NewConfiguration() config.Common.UpdateDepth = 2 Using container As IObjectContainer = Db4oEmbedded.OpenFile(DatabaseFile)
When the update depth is set to a big value on objects with a deep reference hierarchy it will cause each update on the top-level object to trigger updates on the lower-level objects, which can impose a huge performance penalty.
Try transparent persistence, which removes the issue of the update-depth completly.