How to support embedded maps (with custom value types) in MongoDB GORM? - mongodb

Question

I would like to have an embedded document referred to by a map (as in 'class A' below). The environment is Grails + GORM + MongoDB.
is that possible, and if yes, how?
class A { // fails with IllegalArgumentException occurred when processing request: can't serialize class X in line 234 of org.bson.BasicBSONEncoder
static mapWith = "mongo"
Map<String, X> map = new HashMap<String, X>()
}
class B { // works
static mapWith = "mongo"
List<X> list = new ArrayList<X>()
}
class C { // works with primitive type values
static mapWith = "mongo"
Map<String, String> map = new HashMap<String, String>()
}
class X {
String data
public X(String data) {
this.data = data
}
}

Answer 1

The embedding works perfectly,as Art Hanzel advised.
However your problem comes from the fact that you try and use List genericity as a sort of constraint :
Map<String, X>
The problem is that Grails couldn't cope well with this syntax, first because Groovy doesn't support genericity.
However, the MongoDB plugin offers a very powerful functionality that lets you define custom type as Domain Class Properties : see here.
In your case you could have
class A {
static mapWith = "mongo"
MyClass map = new MyClass()
}
Then in your src/java for example you could for example implement a
class MyClass extends HashMap<String,X> { }
Then, of course, you have to define a special AbstractMappingAwareCustomTypeMarshaller to specify how to read and write the property in the DB.
An additional step could also be to add a custom validator to class A to check the validity of data...

Answer 2

The MongoDB Grails plugin documentation describes how to make embedded documents:
class Foo {
Address address
List otherAddresses
static embedded = ['address', 'otherAddresses']
}
Off the top of my head, you should be able to access these via the object graph. I don't see any reason why you shouldn't.
myFoo.address.myAddressProperty...