Make a query to both "id" or "slug" with a single variable - sql

Question

I have a table "articles" where there're "id" and "slug" among other things. On an html page I have a list of links to articles. A link can contain either "id" or "slug" in it.
But if in a URL there's only a number, it doesn't still mean that it's an id -- therefore, casting to int to determine whether or not it's slug or id, won't work.
/articles/my_article
/articles/35
/articles/666 --> still may be slug
I have this sql query:
import (
"github.com/jackc/pgx/v4"
//.........
)
// [..........]
vars := mux.Vars(req)
q1 := `
SELECT
ar.id,
[.........]
FROM
articles AS ar
WHERE ar.slug = $1 OR ar.id = $1`
ar := Article{}
row := db.QueryRow(context.Background(), q1, vars["id_or_slug"])
switch err := row.Scan(&ar.Id, /*[.......]*/); err {
case pgx.ErrNoRows:
wrt.WriteHeader(http.StatusNotFound)
wrt.Write([]byte("article not found"))
case nil:
// good, article found
I get:
ERROR: operator does not exist: bigint = text (SQLSTATE 42883)

Answer 1

You can "attempt" to convert the value to an integer and if the conversion fails just ignore the error and provide an id value known to not be present in the db.
Doing the conversion with Go:
slug := mux.Vars(req)["id_or_slug"]
// option 1:
id, err := strconv.ParseInt(slug, 10, 64)
if err != nil {
id = -1 // provide a value that you're certain will not be present in the db
}
// option 2:
// if id 0 is good enough, you can skip error checking
// and use the following instead of the above.
id, _ := strconv.ParseInt(slug, 10, 64)
query := `SELECT ... FROM articles AS a
WHERE a.slug = $1
OR a.id = $2`
row := db.QueryRow(query, slug, id)
Doing the conversion with postgres: (the following postgres snippet was taken from here.
)
-- first create a postgres function that will do the conversion / cast
create or replace function cast_to_int(text, integer) returns integer as $$
begin
return cast($1 as integer);
exception
when invalid_text_representation then
return $2;
end;
$$ language plpgsql immutable;
... and then utilizing that in go:
slug := mux.Vars(req)["id_or_slug"]
query := `SELECT ... FROM articles AS a
WHERE a.slug = $1
OR a.id = cast_to_int($1::text, -1)` // use the postgres function in the go query string
row := db.QueryRow(query, slug)