Property 'length' does not exists on type ... OkPacket in mysql2 module

Question

I have code similar to this - very simple just to show the case.

this.getCode = (code: string): Promise<codeObject | false> => {
        return new Promise((resolve, reject) => {
            pool.query('SELECT * FROM ?? WHERE code = ?', [TABLE, code], function (err, result) {
                if (err) {
                    return reject(err);
                }

                if (result.length === 0) {
                    return resolve(false);
                }
            });
        });
    };

Problem is in line if (result.length === 0) {, the error is error TS2339: Property 'length' does not exist on type 'RowDataPacket[] | RowDataPacket[][] | OkPacket | OkPacket[]'.

I can not find any way to redefine OkPacket to at least have length?: number that would be enought for ignore that error (most selects do not get OkPackets anyway and i dont wanna have to check type on each select if what i got is not OkPacket when i know it isnt)...

What is your objection to type checking? Seems like the most straight forward way to deal with this. — etarhan, Apr 05 '19 at 09:51
In every function that deals with select (most of them) i would need to find out which result is not OkPacket, when i cannot even get that class to make instanceof check. And i dont want to have milions of lines just checking if constructor name is 'OkPacket' as its quite lame really — Seti, Apr 05 '19 at 11:01

score 7 · Answer 1 · answered Jul 03 '21 at 00:16

I faced a similar issue and was able to fix the warning that TypeScript gives, "Property 'length' does not exist on type 'OkPacket'" by checking to see if the resulting rows from the query was an array. This was a lot easier for me to do than converting the rows to a string with JSON.stringify().

Using the original example above, I'd change the result.length comparison to this:

if (Array.isArray(result) && result.length === 0) {
   return resolve(false);
}

Thank you! This solution worked form me, as well. – Alex_Lima84 Oct 11 '22 at 14:02 — Alex_Lima84, Oct 11 '22 at 14:02

Alexander Reshytko · Answer 2 · 2020-10-20T11:44:39.613

I couldn't find a proper way to handle this either, so ended up with this workaround for my similar case:

const [rows,] = await connection.execute("SELECT id FROM users WHERE email = ?", [profile.email]);
if ((rows as any).length === 1) {
   return (rows as any)[0].id;
}
logger.error("Unexpected query response", rows);
throw Error("This code should never be executed");

You can also use user defined type-guards. Like this:

const isRowDataPacket = (rows: RowDataPacket[] | RowDataPacket[][] | OkPacket | OkPacket[] | ResultSetHeader): rows is RowDataPacket[] | RowDataPacket[][] => {
    return (rows as RowDataPacket[] | RowDataPacket[][]).length !== undefined
}

But you would still need to make a typecast further to interpret each row correctly:

const [rows,] = await connection.execute("SELECT id FROM users WHERE email = ?", [profile.email]);
if (isRowDataPacket(rows) && rows.length === 1) {
    return (rows[0] as { id: string }).id;
}

I ended up checking that damn thing - just checked with as any. — Seti, Oct 21 '20 at 20:44

score 0 · Answer 3 · answered Oct 27 '20 at 07:09

0

I hate this error as well. This is my workaround:

const [rows] = await db.query(`mySqlHere`);
let tempResult: any = rows;

console.log(tempResult.length); // OK

answered Oct 27 '20 at 07:09

Javohir Mirzo Fazliddinov

181
5
15

1

But this makes tempResult as `any` which is not really better for typescript – Seti Oct 27 '20 at 22:59
yes, i know, but i couldn't find a way to make that warning go away. still a lot to learn about typescript – Javohir Mirzo Fazliddinov Oct 28 '20 at 07:12
It's still better than having a type returned you cannot use in my opinion. If youre library is useless but typings are great... it's silly. – Romain Bruckert Jun 30 '21 at 12:29

score 0 · Answer 4 · answered Jun 30 '21 at 12:32

0

I also dislike the design choice on this, but i usually use :

const [rows, fields] = await conn.execute(QUERY_STRING) as any
console.log(rows.length)

answered Jun 30 '21 at 12:32

Romain Bruckert

2,546
31
50

Gogol · Answer 5 · 2023-07-08T08:23:13.880

For my own use case, the map was not defined in OkPacket, because I needed the following

function (error, results, fields) {

            const data = results.map((item: any) => {
                //... do stuffs..
                return {
                    name: item.name,
                    username: item.username,
                    image: item.image,
                    bio: item.bio,
                    url: item.url,
                }
            })
            resolve([results, fields]);
}

To get rid of the error, I ended up checking if map exists in the results object, and making an early return if not (just the reject() won't fix the error). Modified the code as following

function (error, results, fields) {
            if(!('map' in results)) {
                reject(results);
                return;
            }
            const data = results.map((item: any) => {
                // ...do stuff...
                return {
                    name: item.name,
                    username: item.username,
                    image: item.image,
                    bio: item.bio,
                    url: item.url,
                }
            })
            resolve([results, fields]);
}

For your case you could check for the length, for example, and make an early return if it does not exist.

if(!('length' in results)) {
     reject(results);
     return;
}

Property 'length' does not exists on type ... OkPacket in mysql2 module

5 Answers5