科尔马/字段可以采用一列列吗？

Question

I would like to be able to pass a user-defined array of fields which contains a list of all the columns that need fetching. Can korma/fields take an array of columns?

What I am essentially wanting to create is something like this:

(defn fetch [fields]
(->
   (korma/select* foo)

   (as-> query
         (if (not-empty? fields)
           (korma/fields query fields)
           query))

   (korma/select)))

Answer 1

I am assuming this is because I have specified entity-fields in defentity. I am therefore wondering, if it is possible to override the entity-fields specified in defentity ?

I think your assumption is correct, and it's also possible to override this. If you look at the map generated by (defentity foo) it has a :fields key with all the fields. korma.core/entity-fields doesn't replace what's already there, but this will:

(-> foo
    (assoc :fields [:first])
    (korma/select*)
    (korma/as-sql))
=> "SELECT \"foo\".\"first\" FROM \"foo\""

I would like to be able to pass a user-defined array of fields which contains a list of all the columns that need fetching.

(defn fetch [& fields]
  (-> (korma/select* foo)
      (as-> query
        (if (seq fields)
          (assoc query :fields fields)
          query))
      (korma/select)))

I used variadic args in this example to mirror korma.core/entity-fields (and made fetch return the SQL string for my testing rather than execute the query):

(fetch :first :last)
=> "SELECT \"foo\".\"first\", \"foo\".\"last\" FROM \"foo\""
(fetch)
=> "SELECT \"foo\".\"id\", \"foo\".\"first\", \"foo\".\"last\" FROM \"foo\""