Add a way to use multi-indexes in Horizon

[mlucy]

My proposal is that we add a new findContaining command, which behaves like findAll but on a multi-index.

So if you have a document {foo: 'a', bar: ['b', 'c']}, you could look it up with any of these commands

.findAll(foo: 'a')
.findAll(bar: ['b', 'c'])
.findContaining(bar: 'b')

---

I ran into the need for this while working on the web backend for Horizon cloud (@mglukhovsky is using Horizon to write the web interface), where every project has a set of users allowed to push to it, and we need to be able to look up all the projects a user is allowed to push to.

I'm not sure where this should go scheduling-wise, but I think it's pretty important. If we could get it in before we ship Horizon cloud that would save us some really ugly hacks, but I realize that's difficult.

[deontologician]

This looks pretty good. I think the name findContaining is confusing, but having the ability to look up by tags seems like a really common use case we completely ignored.

[deontologician]

maybe containing or findTag ?

[marshall007]

I don't think the object notation is useful in this case because AFAIK we can't support multiple fields in a single query. I'm thinking something like .contains(<field>, <value>, [, <value>... ]), which would check for the presence of any of the specified <value>s.

[mlucy]

I'm not super attached to passing an object, but I think the syntax being the same as for findAll, above, below, etc. is probably valuable. We should probably also support .contains({field: 'foo'}, {field: 'bar'}) if you want to get everything matching either tag. (Also, if we wanted to it's totally possible to support .contains({field: 'foo'}, {field2: 'bar'}) -- we just implement the index on the backend like table.index_create('idx', multi: true){|row| row['field'].map{|x| ['field', x]} + row['field2'].map{|x| ['field2', x]}} and then we turn that query into .getAll(['field', 'foo'], ['field2', 'bar'], index: 'idx').)

[marshall007]

@mlucy 👍 good call, I'm sold on the object notation then. It's a little clunky in the case where you already have an array of values (i.e. .contains(field, values...)), but I'm not sure if it's worth overloading or not.