使用Clojure / Hugsql处理nil参数

Question

I'm using Hugsql with Clojure to access a Postgresql db. Several of my database tables have optional columns - for a simple example consider a "users" table with various address columns - address1, address2, city, etc.

When I write the Hugsql query specification for an "update" I don't know which values will be present in the map I pass in. So if I write a query:

-- :name update-user! :! :n
UPDATE users set firstname = :firstname, address1 = :address1 where id = :id

but pass in a user map

(update-user! {:id "testuser" :firstname "Bartholamew"})

then an exception is thrown. I'd expect it to create something like

UPDATE users SET firstname='Bartholamew', address1=NULL where id='testuser'

I've looked at the Hugsql source - it calls a (validate-parameters) function that throws the exception that I can't see a way around. I'm sure I'm missing something obvious: this doesn't seem like an unusual requirement, and I sure don't want to write a distinct SQL query spec for every possible combination of optional columns.

Is there a way to handle missing parameters that I'm missing? Am I abusing the database by having optional columns?

Answer 1

You can use HugSQL's Clojure Expressions to support conditionally including your desired SQL based on the parameters provided at runtime. So, you can write something like this:

-- :name update-user! :! :n
UPDATE users SET
id = id
--~ (when (contains? params :firstname) ",firstname = :firstname")
--~ (when (contains? params :address1) ",address1 = :address1")
WHERE id = :id

Note: The id=id is a bit silly here to deal with the commas. You can certainly do something more robust and generic with this example from the HugSQL docs:

SQL:

-- :name clj-expr-generic-update :! :n
/* :require [clojure.string :as string]
            [hugsql.parameters :refer [identifier-param-quote]] */
update :i:table set
/*~
(string/join ","
  (for [[field _] (:updates params)]
    (str (identifier-param-quote (name field) options)
      " = :v:updates." (name field))))
~*/
where id = :id

Clojure:

(clj-expr-generic-update db {:table "test"
                             :updates {:name "X"}
                             :id 3})

I'd also encourage you to look at and know what's available in the underlying jdbc library. HugSQL's default adapter is clojure.java.jdbc, and its update! function has similar functionality.