Optional column update if provided value for column is not null - sql

Question

I have following table:
CREATE TABLE IF NOT EXISTS categories
(
id SERIAL PRIMARY KEY,
title CHARACTER VARYING(100) NOT NULL,
description CHARACTER VARYING(200) NULL,
category_type CHARACTER VARYING(100) NOT NULL
);
I am using pg-promise, and I want to provide optional update of columns:
categories.update = function (categoryTitle, toUpdateCategory) {
return this.db.oneOrNone(sql.update, [
categoryTitle,
toUpdateCategory.title, toUpdateCategory.category_type, toUpdateCategory.description,
])
}
categoryName - is required
toUpdateCategory.title - is required
toUpdateCategory.category_type - is optional (can be passed or undefined)
toUpdateCategory.description - is optional (can be passed or undefined)
I want to build UPDATE query for updating only provided columns:
UPDATE categories
SET title=$2,
// ... SET category_type=$3 if $3 is no NULL otherwise keep old category_type value
// ... SET description=$4 if $4 is no NULL otherwise keep old description value
WHERE title = $1
RETURNING *;
How can I achieve this optional column update in Postgres?

Answer 1

You could coalesce between the old and the new values:
UPDATE categories
SET title=$2,
category_type = COALESCE($3, category_type),
description = COALESCE($4, description) -- etc...
WHERE title = $1

Answer 2

The helpers syntax is best for any sort of dynamic logic with pg-promise:
/* logic for skipping columns: */
const skip = c => c.value === null || c.value === undefined;
/* reusable/static ColumnSet object: */
const cs = new pgp.helpers.ColumnSet(
[
'title',
{name: 'category_type', skip},
{name: 'description', skip}
],
{table: 'categories'});
categories.update = function(title, category) {
const condition = pgp.as.format(' WHERE title = $1', title);
const update = () => pgp.helpers.update(category, cs) + condition;
return this.db.none(update);
}
And if your optional column-properties do not even exist on the object when they are not specified, you can simplify the skip logic to just this (see Column logic):
const skip = c => !c.exists;
Used API: ColumnSet, helpers.update.
See also a very similar question: Skip update columns with pg-promise.