Document::Transform - Pull and transform documents from a NoSQL backend


version 1.110530


    use Try::Tiny;
    use Document::Transform;
    use Document::Transform::Backend::MongoDB;

    my $backend = Document::Transform::Backend::MongoDB->new(
        host => $ENV{MONGOD}
        database_name => 'foo',
        transform_collection => 'transforms',
        document_collection => 'documents');

    my $transform = Document::Transform->new(backend => $backend);

    my $result;

        $result = $transform->fetch(
            MongoDB::OID->new(value => 'SOME_DOCUMENT'));
        warn 'Failed to fetch the document';


Ever need to fetch a document from some NoSQL source, and wanted a way to store only the specific changes to that document in a separate document and magically combine the two when you ask for the more specific document? Then this module will help you get that pony you've always wanted.

Consider the following JSON document:

        "document_id": "QWERTY1",
        "foo": "bar",
        "blarg": "sock puppets rock"

This is an awesome, typical document stored in something like MongoDB. Now, what if we had hundreds of other documents that were all the same except the "blarg" attribute was slightly different? It would be wasteful to store all of those whole complete documents. And what if we wanted to update them all? That could potentially be expensive. So what is the solution? Store a core document, and store the set of changes to morph it into the more specific or different document separately. Then when you update the core document, everything else continues to work without manually touching all of the other documents.

So what does a transform look like? Like this:

        "transform_id": "YTREWQ1",
        "document_id": "QWERTY1",
                "path": "/yarg/*[0]",
                "value": "ONE"
                "path": "/foo",
                "value": "BAR"
                "path": "/qwak/farg",
                "value": { "yarp": 1, "narp": 0 }

Jumpin' jehosaphat! What is all of that line noise? So, you can see how this transform references the core document via the document_id attribute. The transform_id is what we use to fetch this transform. The operations attribute holds an array of tuples. Each tuple is merely a Data::DPath path specification and a value to be used at that location. What is a Data::DPath path? Well, it is like XPath but for data structures. It is some good stuff.

So the first two operations look simple enough. We reference locations that exist and replace those values with all caps versions, but what about the last operation? The original document doesn't have anything that matches that path. Well, you're in luck. If your path is simple enough, the transformer will create that path for you and dump your value there for you. Now, let me stress "simple enough." It needs to be straight hashes, no filters, no array access, etc. So, '/this/path/rocks' will work just fine. '/this/*[4]/path/sucks' will not work. If you would like it to work, you are more than welcome to implement your own transformer. Simply consume the interface role Document::Transform::Role::Transformer and implement the transform method and pass in an instance and you are set.

Something else this module does is allow you to have transforms reference other transforms that reference other transforms, and so on until it reaches a source document. Please be careful that the transforms dont ultimately make a giant circular linked list that will never resolve to a document. There are checks in place to throw an exception if a transform has already been seen when attempting to get a document, but the checks are naive and only look at the "transform_id_key" in Document::Transform::Role::Backend. If this key is not unique in your NoSQL store, then you are screwed. You've been warned.

This module ships with one backend and one transformer implemented but you aren't married to either if you don't like MongoDB or think the transformer semantics are subpar. This module and its packages are all very Bread::Board friendly.



    is: ro, does: Document::Transform::Role::Backend, required: 1

The backend attribute is required for instantiation of the Document::Transform object. The backend object is what talks to whichever NoSQL resource to fetch and store documents and transforms.

You are encouraged to implement your own backends. Simply consume the interface role Document::Transform::Role::Backend and implement the required methods.


    is: ro, does: L<Document::Transform::Role::Transformer>
    builder: '_build_transformer', lazy: 1

The transformer is the object to which transformation responsibilities are delegated. By default, the Document::Transform::Transformer class is instantiated when none is provided. Please see its documentation on the expectations of document and transform formats.

If you would like to implement your own transformer (to support your own document and transform formats), simply consume the interface role Document::Transform::Role::Transformer and implement the transform method.


    is: ro, isa: CodeRef

post_fetch_callback simply provides a way to do additional processing after the document has been fetched and transform executed. One good use for this is if validation of the result needs to take place. This coderef is called naked with a single argument, the final document. Throw an exception if execution should stop. The return value is discarded.




fetch performs a transform lookup using the provided key argument, then a document lookup based information inside the transform(which can recurse as transforms can reference other transforms until a document is reached). Once it has both pieces (all of the transforms and the document), it passes them on to the transformer via the transform method. The result is then passed to the callback "post_fetch_callback" before finally being returned.

If for whatever reason there isn't a transform with that key, but there is a document with that key, the document will be fetched and not transformed. It is still subject to the "post_fetch_callback" though.

In list context, the transformed document along with the transforms executed are returned. Otherwise, just the transformed document is returned.


    (Backend constrained document or transform)

store takes a single item as an argument and depending on the the type constraints from the backend it will execute the appropriate store method on the backend. See "document_constraint" in Document::Transform::Role::Backend and "transform_constraint" in Document::Transform::Role::Backend for more information



A document fetch is attempted with the provided argument. If successful, it returns true.



A transform fetch is attempted with the provided argument. If successful, it returns true.


Nicholas R. Perez <>


This software is copyright (c) 2010 by Infinity Interactive.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.