Spring Data + MongoDB GridFS access via Repository possible?

Question

I recently discovered GridFS which I'd like to use for file storage with metadata. I just wondered if it's possible to use a MongoRepository to query GridFS? If yes, can someone give me an example?

I'd also take a solution using Hibernate, if there is some.

The reason is: My metadata contains a lot of different fields and it would be much easier to query a repository than to write some new Query(Criteria.where(...)) for each scenario. And I hopefully could also simply take a Java object and provide it via REST API without the file itself.

EDIT: I'm using

• Spring 4 Beta
• Spring Data Mongo 1.3.1
• Hibernate 4.3 Beta

Answer 1

There is a way to solve this:

@Document(collection="fs.files")
public class MyGridFsFile {

    @Id
    private ObjectId id;
    public ObjectId getId() { return id; }

    private String filename;
    public String getFilename() { return filename; }

    private long length;
    public long getLength() { return length; }

    ...

}

You can write a normal Spring Mongo Repo for that. Now you can at least query the fs.files collection using a Spring Data Repo. But: You cannot access the file contents this way.

For getting the file contents itself, you've got (at least) 2 options:

1. Use file = gridOperations.findOne(Query.query(Criteria.where("_id").is(id))); InputStream is = file.getInputStream();

2. Have a look at the source code of GridFSDBFile. There you can see, how it internally queries the fs.chunks collection and fills the InputStream.

(Option 2 is really low level, Option 1 is a lot easier and this code gets maintained by the MongoDB-Java-Driver devs, though Option 1 would be my choice).

---

Updating GridFS entries:

• GridFS is not designed to update file content!
• Though only updating the metadata field can be useful. The rest of the fields is kinda static.

You should be able to simply use your custom MyGridFsFileRepo's update method. I suggest to only create a setter for the metadata field.

---

Different metadata for different files:

I solved this using an abstract MyGridFsFile class with generic metadata, i.e.:

@Document(collection="fs.files")
public abstract class AbstractMyGridFsFile<M extends AbstractMetadata> {

    ...

    private M metadata;
    public M getMetadata() { return metadata; }
    void setMetadata(M metadata) { this.metadata = metadata; }

}

And of course each impl has its own AbstractMetadata impl associated. What have I done? AbstractMetadata always has a field called type. This way I can find the right AbstractMyGridFsFile impl. Though I have also a generic abstract repository.

Btw: In the meantime I switched here from using Spring Repo, to use plain access via MongoTemplate, like:

protected List<A> findAll(Collection<ObjectId> ids) {
    List<A> files = mongoTemplate.find(Query.query(Criteria
            .where("_id").in(ids)
            .and("metadata.type").is(type) // this is hardcoded for each repo impl
    ), typeClass); // this is the corresponding impl of AbstractMyGridFsFile
    return files;
}

Hope this helps. I can write more, if you need more information about this. Just tell me.