Question

I have a mapping in MongoDB as type hash, named “meta_info” which simply holds a key/value list of something, I’d like to make it to a form in Symfony2 which can be enhanced dynamically (with js), to have it look (basically) like this:

<input type="text" name="meta_info[key][]" /><input type="text" name="meta_info[field][]">   [- remove row]
<input type="text" name="meta_info[key][]" /><input type="text" name="meta_info[field][]">   [+ add row]

My first ideas were to make two textfields (key/value) which can be duplicated using js (thats not the problem) and which get converted to a json string onSubmit and converted back to an array inside my setter method of my Document class.. But this seems kinda dirty..

I was also thinking about embedding forms (which works very well with embedded documents now in sf2.1!) – but I don’t know how to achieve this for a simple key/value hash (which should also be stored like that in mongodb)

Thanks for any ideas and approaches!

Answer 1

Thinking about this in terms of Symfony forms, you likely want to have a dynamic collection of inner forms, each of which has key and value input fields. I can’t think of another implementation to handle this case, as you’re essentially foregoing any notion of a schema by using a hash field. That’s mainly what distinguishes this case from embedded documents in ODM (which would have mappings), even though MongoDB is going to store in the same manner (nested objects).

One alternative implementation is to have an EmbedMany relationship of documents that contain key and value properties. OpenSky uses this internally to represent product attributes. It consumes a bit more storage in the MongoDB document, since you have an array of objects with key and value fields instead of a single object of key/value pairs, but there are some clear benefits:

• The structure can be mapped, which plays nicely with your existing ODM schema.
• Since you have a model for each key/value pair, it’s more natural to represent this with Symfony forms.
• Perhaps most importantly if you’re going to query by this data, you can take advantage of multi-key indexing to index dynamic keys and values and then use $elemMatch queries for key/value lookups. If you were just using a hash field with dynamic keys, there would be no straightforward way to index multiple keys (each distinct field path would require an explicit index, or explicit mention in a compound index).