具有一对多关系的Grails数据绑定-链接回父级的链接丢失

Question

In a Grails 2.2.2 application, I have a one-to-many relationship that looks something like this:

Parent:

class Client {
    ...
    String name
    static hasMany = [modelFieldInstances: ModelFieldInstance]
    ...
}

Child:

class ModelFieldInstance {
    ...
    String name
    String value
    static belongsTo = [client: Client]
    ...
}

I'm trying to create a data importer so that users can import a spreadsheet or csv containing their client records. To do this, I inspected the parameters that grails scaffolding uses when it creates a new Client instance in the save method of the standard scaffolding controller.

The problem is that when I try to create and save a new Client instance with my importer, the child ModelFieldInstance s are saved without their reference to the parent Client (the Client and the ModelFieldInstance s all get persisted though).

In my importer, I'm doing the data binding like this:

Client client = new Client()
client.modelFieldInstances = ListUtils.lazyList(new ArrayList(), {new ModelFieldInstance()} as org.apache.commons.collections.Factory)
client.properties = properties
...
client.save()

I think the only real difference between how the Grails scaffolding controller works and how my importer works is that in my importer I'm initially setting the modelFieldInstances collection as a LazyList . However, before I added the LazyList assignment the data binding was blowing with an error like this:

Invalid property 'modelFieldInstances[31]' of bean class [com.myapp.Client]: Illegal attempt to get property 'modelFieldInstances' threw exception; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'modelFieldInstances[31]' of bean class [com.myapp.Client]: Cannot get element with index 31 from Set of size 0, accessed using property path 'modelFieldInstances[31]'**

So, I guess the question is, why doesn't the data binding work in my data importer when I can see that it does work in the scaffolding controller for a given properties map.

Answer 1

As a sort of work around, I implemented a method that iterates over all the items in the modelFieldInstances collection and manually assigns the parent ( client ) to each one. This seems to work fine, however I'm still unsure as to why grails data binding doesn't do this for me. I wonder if there's some magic happening in GrailsParameterMap ...