Knex.js SQL syntax error near 'select' - postgresql

Question

I'm getting an odd error:
{ __cid: '__cid9',
method: 'insert',
options: undefined,
bindings:
[ 500,
'Dinner',
'10/02/2015 7:57 PM',
'09/29/2015 8:00 PM',
'Grand Plaza',
1 ],
sql: 'insert into "expense" ("amount", "description", "due_date", "payment_date", "vendor_id") values ($1, $2, $3, $4, select "vendor_id" from "vendor" where "name" = $5 limit $6)',
returning: undefined }
error: syntax error at or near "select"
at [object Object].Connection.parseE (/.../node_modules/pg/lib/connection.js:534:11)
at [object Object].Connection.parseMessage (/.../node_modules/pg/lib/connection.js:361:17)
at Socket.<anonymous> (/.../node_modules/pg/lib/connection.js:105:22)
at Socket.emit (events.js:107:17)
at readableAddChunk (_stream_readable.js:163:16)
at Socket.Readable.push (_stream_readable.js:126:10)
at TCP.onread (net.js:538:20)
I have run the raw SQL with those value cut and paste and it works just fine.
This is the code thats generating the error:
Promise.each subbudget.expenses, (expense) ->
vendor.get(expense.vendor).then (vendor_id) ->
knex('expense').insert(
due_date: expense.dueDate
vendor_id: (knex.first("vendor_id").from("vendor").where({name: vendor_id}))
amount: expense.amount
description: expense.description
payment_date: expense.paidDate
)
Edit (Partial Solution):
The issue seems to be parentheses missing around the SELECT statement. Knex offers .wrap(), which only works on raw, and .as(), which only works on nested statements; for some reason this does not qualify as a nested statement, so I can't get parentheses around it. Any ideas?

Answer 1

knex.raw("(" + knex.first("vendor_id").from("vendor").where({name: vendor_id}).toString() + ")")
Not the cleanest, but use .toString(), then wrap it in .raw()