Question

I come from a SQL world where lookups are done by several object properties (published = TRUE or user_id = X) and there are no joins anywhere (because of the 1:1 cache layer). It seems that a document database would be a good fit for my data.

I am trying to figure-out if there is a way to pass one (or more) object properties to a CouchDB map/reduce function to find matching documents in a database without creating dozens of views for each document type.

Is it possible to pass the desired document property key(s) to match at run-time to CouchDB and have it return the objects that match (or the count of object that match for pagination)?

For example, on one page I want all posts with a doc.user_id of X that are doc.published. On another page I might want all documents with doc.tags[] with the tag “sport”.

Answer 1

You could build a view that iterates over the keys in the document, and emits a key of [propertyName, propertyValue] – that way you’re building a single index with EVERYTHING prop/value in it. Would be massive, no idea how performance would be to build, and disk usage (probably bad).

Map function would look something like:

// note - totally untested, my CouchDB fu is rusty
function(doc) {
  for(prop in doc) {
    emit([prop, doc[prop]], null);
  }
}

Works for the basic case of simple properties, and can be extended to be smart about arrays, and emit a prop/value pair for each item in the array. That would let you handle the tags.

To query on it, set [prop] as your query key on the view.