Hi,
In past years I've spend quite some time converting MMBase node graphs
to strongly typed object graphs. One of the reasons for doing this is
to define 'meta' models on top of the cloud. 'What is a
newsitem?' (i.e. which rules need to be applied to get all the needed
data from MMBase).
Due to recent developments within the VPRO I decided to have another
go at it. And I came up with a working prototype of something which I
think might be useful to others; or where others might be able to
provide valuable feedback!
The small framework I created is annotation based; i.e. you specify
the bindings to MMBase using annotations:
// --------- NewsItem.java
@Entity(builder = "news", root = true)
public class NewsItem {
private Long number;
private String title;
private String subtitle;
private String credits;
@Field(nodeField = "intro")
private String description;
private String body;
@Embedded(builder = "mmevents", field = "start", convertor =
EpochDateConvertor.class)
private Date created;
@PosRel(orderDirection = Direction.DESC, queryDirection =
QueryDirection.BOTH)
private List<Image> image;
@Rel(orderDirection = Direction.DESC, orderField = "value",
queryDirection = QueryDirection.DESTINATION)
private List<Tag> tag;
// --------- Image.java
@Entity(builder = "images")
public class Image {
private Long number;
private String title;
// --------- Tag.java
@Entity(builder = "tags")
public class Tag {
private Long number;
private String value;
The implementation is still in concept phase, but as you can see it is
already possible to define mappings for associations (works for type
collections only), fields (populated by default, @Field annotation use
to override properties) and associations which are treated as embedded
objects. Note: at the moment I'm only considering read operations.
Entity definitions are automatically retrieved at startup of a simple
MMBase module, after which binding can be done as follows:
// retrieve node from mmbase
Node node = cloud.getNode(nodeNumber);
// find the root entity in the registry
Object newEntityInstance =
entityRegistry.get(builderName).newInstance();
// transform the node to the specified entity
Populator.unmarshallNode(newEntityInstance, node);
There is still a lot of ground to cover, but the basics work, and the
populator class is still less then 200 lines of code! No public
sourcecode yet, but I'd be more than happy to contribute it in the
near future if others are interested.
looking forwards to ideas, criticism etc.
Peter
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