How to select default fields in korma?

Question

Assume you have already done a defdb. I have a table "items" which has two fields, "id" (PK) and "item". I want to set up an entity so that whenever I select it, I only get the entries in "item". Judging by the documentation I thought korma/entity-fields was the way to do this.

(require '[korma.core :as korma])

(korma/defentity items
  (korma/entity-fields :item))

(korma/select items)
;; Wanted: [{:item "foo"}]
;; Received: [{:id 1, :item "foo"}]

I'm using korma 0.3.0-beta7. How can I make korma/select do what I want?

Eve Freeman · Accepted Answer · 2012-10-25T18:14:16.583

1

I don't think you can do this from the defentity--the way select works without passing a list of fields explicitly is just select *.

How about a helper-macro based on korma/select:

(defmacro select-without-id
  [ent & body]
  `(let [query# (-> (korma/select* ~ent)
                (korma/fields (vec (:fields ~ent)))
                 ~@body)]
     (korma/exec query#)))

edited Oct 25 '12 at 18:14

answered Oct 25 '12 at 17:57

Eve Freeman

32,467
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Do you know what "entity-fields" does then? The doc says "Set the fields to be retrieved by default in select queries for the entity." – ToBeReplaced Oct 25 '12 at 18:12
Maybe I'm totally off, but I don't see how it does that. It looks like it defines the fields for the entity (the columns in the table). Unless you send a `(fields)` to `(select)`, it looks like it just does `select items.*`. I added a helper macro that might work for you. I'm kind of a korma noob, though, so don't take anything I say as gospel. – Eve Freeman Oct 25 '12 at 18:18

score 0 · Answer 2 · answered Oct 25 '12 at 17:22

0

id is a defauld PK column name in Korma. That's why you see it in result list. You can remove it by using transform definition:

(korma/defentity items
  (korma/entity-fields :item)
  (korma/transform #(dissoc % :id)))

answered Oct 25 '12 at 17:22

zvez

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If you change my example to `(korma/entity-fields :id)` you still get the same result (that is, the :item is still in the result). Your answer is incorrect, though it is true that transforms could be used to remove unwanted keys. – ToBeReplaced Oct 25 '12 at 17:29

dizzystar · Answer 3 · 2012-11-03T23:34:20.390

Try creating a new namespace with the following dependencies:

(ns yourproject.path.kormastuff
    (:use [korma.core]
          [korma.db]))

Then create your entities as such:

(defentity items
  (entity-fields :item))

I think you're probably hitting a wall because you are trying to alias a core and you are missing the db. It's much better to push this stuff into its own file and call the queries you want, with aliases if you chose, from other namespaces, ie:

(ns project.core
    (:use [project.path.kormastuff :as kormadb]))

Then:

(select kormadb/items)

to get your results. That should work.

In the REPL, simply enter

items

into the command prompt to see the output Korma will give you. There should be no other fields showing up. If you run (select items) in the REPL it will show up everything whether you want that to happen or not. To get the real output you probably have to do a (format "%s" items) in a browser window or something.

If all that doesn't work, there's no shame in using the normal (select db (fields [:item])) clause. You'll find you'll be forced to destructure to use the information anyways.

EDIT:::::::

I'm sorry, I didn't explain myself clearly.

You aren't supposed to do

(select kormadb/items)

to get what you want. You only need to call the entity itself, so you only need to call items in the REPL, NOT (select items) in the REPL.

You would want to do something like

(def myQuery kormadb/items)

$ myQuery

and you will see that there are no other fields selected by default.

You can also do

(let [myQuery kormadb/items] 
    (format "%s" myQuery))

I'm modifying here, but what I get is similar to this:

{:table "items", :name "items", :pk :id, :db nil, :transforms (), :prepare
s (), :fields ("\"items\".\"item\""), :rel {}}

In order to use myQuery, you need to destructure the above hash-map. I'll leave that as an exercise for you to learn because destructuring is important and hard to learn unless you get your own hands dirty, but I'll give you a little place to start that won't give you an answer, but won't throw an error either:

(let [{myAlias :fields} myQuery]
    (format "%s" myAlias))

What do you mean by alias a core, and what do you mean by missing the db? I just set a project up as you suggested with "use" and separate files, and got the same result as before. Can you confirm that when you do `(select kormadb/items)` you get only the item column? — ToBeReplaced, Nov 01 '12 at 12:53
I added some more clarification to the answer. I think I've given you plenty. I strongly encourage you to just use (select items (fields....)) because it should be much easier. — dizzystar, Nov 03 '12 at 23:36

How to select default fields in korma?

3 Answers3