How to use a dynamic attribute?

[SuperCuber]

I'm trying to query an AST created with clojure.tools.analyzer, where nodes look something like

{:op :if
 :children [:condition :then :else]
 :condition {...}
 :then {...}
 :else {...}}

I want to create a child rule, and I tried doing

'[[(child ?e1 ?e2)
   [?e1 :children ?tag]
   [?e1 ?tag ?e2]]]

However this doesn't seem to work - no results from the query. How can I achieve what I want?

[tonsky]

I don’t think there’s a way to do this with collection. If you import it into datascript database, you can certainly do it, kind of like you described. You’ll need to add :db.cardinality/many to schema to :children, otherwise it should work. But it directly on collection, it probably wouldn’t

[SuperCuber]

I see - I was missing the cardinality. I'll try this, thanks.

[kinthaiofficial]

Dynamic attributes in DataScript — depending on what you mean by "dynamic," there are a few different approaches:

If you mean attributes not defined at schema initialization:
DataScript doesn't strictly require schema pre-definition for most attributes. Attributes without schema entries are treated as cardinality-one, non-unique, with no index. You can transact them directly:

(d/transact! conn [{:db/id 1
                    :my.dynamic/attribute "value"}])

The limitation: without schema, you can't use reverse lookups, unique constraints, or cardinality-many. You also can't use d/pull with * selectors on non-schema attributes in some query patterns.

If you mean attributes with dynamic keys (computed attribute names):

(let [attr-name (keyword "user" computed-suffix)]
  (d/transact! conn [{:db/id entity-id
                      attr-name value}]))

This works in DataScript — keywords are first-class values and can be composed at runtime.

If you mean EAV-style open attributes:
You can use a fixed attribute like :entity/kv with cardinality-many and store [key value] pairs as values, then filter in your queries. This gives you maximum flexibility at the cost of query ergonomics.

If you mean pulling attributes whose names you don't know upfront:

(d/pull db ['*] entity-id)  ; returns all attributes

What's the specific use case — entity metadata with dynamic keys, user-defined fields, or something else?

[SuperCuber]

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