Why my strict comparison returns nothing

You saw this warning:

Routier: 'price' is a number, and this filter compares it against "5", which is a string.
A strict comparison between them is the same answer for every row, so no row matches and
the filter runs in memory.

Your filter compares a column against a value of a different type, with === or !==. JavaScript answers that comparison the same way for every row, so the filter cannot select anything.

The cause

=== compares type as well as value. 5 === "5" is false in JavaScript, whatever the row holds.

// price is s.number()
const price = req.query.price;      // "5" — a string, from the URL

await ctx.products.where(p => p.price === price).toArrayAsync();
// 0 rows, always

The value usually arrives as a string from a form, a URL, a query parameter, or JSON.parse of a field that was serialized as text.

What Routier does

Routier detects the mismatch and runs the filter in memory rather than in the database. The rows you get are the rows JavaScript gives you.

.explain() reports it:

STEP 1 of 1 — memory  [predicate-error]
    filter   price === "5"

Routier does not correct your filter. Correcting it would mean guessing which of the two types you meant, and a wrong guess returns rows you did not ask for.

Both directions

filter	rows returned
p.price === "5"	none
p.price !== "5"	every row

The second one is the dangerous one. It looks like it filters, and it does not.

How to fix it

Convert the value to the column's type before the filter. This is the recommended fix.

const price = Number(req.query.price);

await ctx.products.where(([p, params]) => p.price === params.price, { price }).toArrayAsync();

If you want JavaScript's coercing comparison, use == or !=. Routier coerces the value to the column's type for a loose comparison, and pushes the filter down.

await ctx.products.where(p => p.price == "5").toArrayAsync();
// 1 row, and it runs in the database

Which types Routier checks

schema type	JavaScript type it must be compared against
s.number()	number
s.string()	string
s.boolean()	boolean
s.date()	Date

A null or undefined value is never a mismatch: p.name === null is a legitimate filter.

A bigint compared to a s.number() column is a mismatch, because 5 === 5n is false in JavaScript.

Turning the warning off

The warning goes through Routier's logger, at warn level.

ROUTIER_LOG_LEVEL=error   # or: silent

Turning the warning off does not change the rows. The filter still runs in memory, and still returns what JavaScript returns.

Related

• Filtering
• .explain()
• Creating a schema