[lneves]

Yes I've looked at them. I use them every day. The example you posted its difficult to parse because it deals with multidimensional arrays and also populating one in the inner query. The simple, and much more common case of one dimension arrays is very straightforward. Can you show me the equivalent in MongoDB?

About the performance/scalability warning; I don't deal with very large arrays, a couple hundred items max, and when using a GIN index over the array field, search queries are screamingly fast.

[w1nk]

Sure, check out:

http://www.mongodb.org/display/DOCS/Dot+Notation+%28Reaching...

[lneves]

I do not think that this is equivalent, it looks like querying complex JSON objects and not "simple" arrays.

From the "Array Element by Position" example:

  db.blogposts.find( { "comments.0.by" : "Abe" } )

PostgreSQL doesn't have JSON support but it does have XML/Xpath support.

If you stored XML documents in PostgreSQL the similar query to the MongoDB one would be something like this:

  select * from blogposts where (xpath('/comments[0]/@by', doc))::text[] = array['Abe']

Yes it's a little more verbose but not terrible so... at least in my opinion.