Passing function to Knex select method breaks querying - node.js

Question

The code:
const knex = require("../../db/knex");
module.exports = (request, response) => {
knex
.select((builder) => {
const select = request.query.select;
if (select) {
if (select.constructor === String) {
builder.select(select);
} else if (select.constructor === Array) {
builder.select(...select);
}
} else {
/* Anything that goes here or inside this function, breaks it. */
}
})
.from("tags")
.where((builder) => {
const filter = request.query.filter;
if (filter) {
if (filter.constructor === Object) {
builder.where(filter);
} else if (filter.constructor === Array) {
builder.where(...filter);
}
} else {
builder.clear("where");
}
})
.then((result) => response.json(result))
.catch((error) => response.json({ ...error, message: error.stack }));
};
The full error:
{
"length": 180,
"name": "error",
"severity": "ERROR",
"code": "42601",
"position": "16",
"file": "d:\\pginstaller_13.auto\\postgres.windows-x64\\src\\backend\\parser\\parse_target.c",
"line": "1296",
"routine": "ExpandAllTables",
"message": "error: select (select *) from \"tags\" - SELECT * with no tables specified is not valid\n at Parser.parseErrorMessage (C:\\Users\\Lucas\\Desktop\\Repositories\\projeto-integrador-dh-g1\\node_modules\\pg-protocol\\dist\\parser.js:278:15)\n at Parser.handlePacket (C:\\Users\\Lucas\\Desktop\\Repositories\\projeto-integrador-dh-g1\\node_modules\\pg-protocol\\dist\\parser.js:126:29)\n at Parser.parse (C:\\Users\\Lucas\\Desktop\\Repositories\\projeto-integrador-dh-g1\\node_modules\\pg-protocol\\dist\\parser.js:39:38)\n at Socket.<anonymous> (C:\\Users\\Lucas\\Desktop\\Repositories\\projeto-integrador-dh-g1\\node_modules\\pg-protocol\\dist\\index.js:10:42)\n at Socket.emit (events.js:315:20)\n at addChunk (internal/streams/readable.js:309:12)\n at readableAddChunk (internal/streams/readable.js:284:9)\n at Socket.Readable.push (internal/streams/readable.js:223:10)\n at TCP.onStreamRead (internal/stream_base_commons.js:188:23)"
}
I'm using Express to manage the Node server and Knex to manage the database. In this route, if I remove the function from select, everything works. Tried everything, I can't understand why isn't working. Can anyone help me understand why is it breaking?

Answer 1

The select() method in Knex takes in column names to select from your table. I don't think you can properly pass in a function like you're trying to do. You can do that in the .where() like you have. But I'd start by removing all of the if/else logic from inside of select().
If you need to transform the data you're receiving, do that prior to building a query. Perhaps there might be other query building methods that would help you get the result that you're looking for.

Answer 2

As stated in the comment, what is being done is considered by Knex a sub query. I've found out that the proper way to handle these conditions are by using modify.
I got to something like this now:
const knex = require("../../db/knex");
module.exports = (request, response, next) => {
knex
.from("tags")
.modify((builder) => {
const filter = request.query.filter;
const select = request.query.select;
const order = request.query.order;
const id = request.params.id;
if (select) {
if (select.constructor === String || select.constructor === Object) {
builder.select(select);
} else if (select.constructor === Array) {
builder.select(...select);
}
}
if (id) {
builder.where({ id: id }).first();
} else if (filter) {
if (filter.constructor === Object) {
builder.where(filter);
} else if (filter.constructor === Array) {
builder.where(...filter);
}
}
if (!id) {
if (order) {
if (order.constructor === String) {
builder.orderBy(order);
} else if (order.constructor === Array) {
builder.orderBy(...order);
}
}
}
})
.then((result) => response.json(result))
.catch((error) => next(error));
};