Partial Model Population by DAO

[Neil Chaudhuri]

Just curious if there is a way to only populate a portion of the model class. I'm aware of projections, but I am curious if it is possible to return the model class itself populated with a subset of components rather than the individual components themselves.

Trying projection[MyModel](MongoDBObject("field" -> field), "_id") didn't work for me.

Thanks.

[rose katherine toomey]

Hi Neil,

The answer is: yes. As long as the fields you're not bringing back all have default values, you can include or exclude whatever you like.  This can really speed up retrieval. 

Best,

Rose. 

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[Neil Chaudhuri]

That was why I was looking into it. Now I'm going to check all my excluded fields have defaults.

Thanks.

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[Neil Chaudhuri]

I have added defaults for all my fields, but I still can't get a partial projection to work.

This does work: MyModelDao.projection[Files](MongoDBObject("uniqueIdentifier" -> "identifier"), "files")

where Files is a component case class of MyModel.

This does not work: MyModelDao.projection[MyModel](MongoDBObject("uniqueIdentifier" -> "identifier"), "")

And by "not work," I mean the preceding call returns None while the other returns Some.

If we assume I haven't missed a default value somewhere, can you point out where my call is flawed? I have a feeling empty string (I also tried "{}" and "*") isn't the way to go.

Thanks.

[rose katherine toomey]

You don't need to project - just do a find it findOne, the first argument is the query and the second is the inclusions/exclusions. See the docs for the syntax since my phone will mangle it for sure....

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[Neil Chaudhuri]

I've scoured the documentation, Scaladoc, and the tests, but whatever I try in the REPL doesn't work for me (in various ways). Please let me know the syntax at your convenience.

Thanks.

[Neil Chaudhuri]

Any chance you can give me the syntax for a partially loaded model? Or at least point me to a resource (doc, test, whatever) that shows an example?

Thanks.

[rose katherine toomey]

Hi Neil,

http://docs.mongodb.org/manual/reference/method/db.collection.find/#db.collection.find

object Bar {

  val empty = Bar(/*etc*/)

}

case class Bar(/* bar stuff*/)

object Baz {

  val empty = Baz(/*etc*/)

}

case class Baz(/* baz stuff */)

case class Foo(_id: ObjectId, bar: Bar = Bar.empty, baz: Baz = Baz.empty)

// whitelist: bring back foo documents with just _id and bar fields

FooDAO.find(MongoDBObject(/*query*/), MongoDBObject("bar" -> 1, "_id" -> 1))

// blacklist: bring back foo documents without baz field

FooDAO.find(MongoDBObject(/*query*/), MongoDBObject("baz" -> 0))

Does this help?

Best,

Rose

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[Neil Chaudhuri]

Yes. That worked great. Thanks for your help, Rose. 

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Neil Chaudhuri, M.S., PMP, CSM, CSP
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