How to correctly use om/transact! to add a new entry to a list

[Roger Gilliar]

services is a cursor to an array.

The following works:

(let [new-services (conj @services {:name (str "New " (inc (count @services)))})]
(om/update! services new-services))

the following doesn't

(om/transact! services conj {:name (str "New Service ")})

and gives me:

Uncaught Error: Vector's key for assoc must be a number.

Why ?

[Daniel Kersten]

om/transact takes a path as its third argument (a key or a vector of keys), but you are passing in a function (conj):

https://github.com/swannodette/om/wiki/Documentation#transact

With om/update! you are using the 2 parameter variant, which is why that works: https://github.com/swannodette/om/wiki/Documentation#update

The versions of om/transact! are:

(om/transact! cursor function)

(om/transact! cursor path function)

(om/transact! cursor path function tag)

Note that it's not like swap! where you can pass additional arguments to function after the function.

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[Toni Helenius]

(om/transact! services (fn [services] (conj services {:name (str "New service")})))

transact! is a bit different from swap because it is more focused on updating just a part of the map that is the app state.

[Andrew Stoeckley]

On Wednesday, May 7, 2014 2:30:26 PM UTC+8, Daniel Kersten wrote:

> The versions of om/transact! are:
>
> (om/transact! cursor function)
> (om/transact! cursor path function)
> (om/transact! cursor path function tag)
>
> Note that it's not like swap! where you can pass additional arguments to function after the function.
>

I'm trying to understand the line in the documentation that says:

om.core/transact! can be given additional args to pass to f.

This implies there is a multiple arity variant of transact! ? What is meant by this line in the docs, as I've never seen any examples of it.

Andrew

[Dave Della Costa]

Hi Andrew,

I assume what was intended was the same as how update-in behaves:

http://clojure.github.io/clojure/clojure.core-api.html#clojure.core/update-in

However, reading the source for Om makes it clear that this is not
supported:

https://github.com/swannodette/om/blob/master/src/om/core.cljs#L776-L790

So this must be a mistake in the documentation--perhaps transact! used
to do this but no longer does. I suspect whenever David added the tag
argument he removed this functionality.

In any case I've removed this line from the wiki docs.

DD

[Andrew Stoeckley]

Awesome, thanks for clearing this up.

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