Question

I was previously using sqlite3 for my ruby code and it worked fine for the following code

def existsCheck( db, id )
    temp = db.exec( 'SELECT 1 WHERE EXISTS(
        SELECT 1
        FROM Products
        WHERE promoID = ?
    ) ', [id] ).length > 0
end


def writeDB( db, product )
    db.exec( 'INSERT INTO Products ( promoID, name, price, shipping, condition, grade, included, not_included, image, time_added )
                        VALUES ( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)', [product.promoID, product.name, product.price, product.shipping, product.condition, product.grade, product.included, product.notIncluded, product.image, product.time] )
end

Does Postgresql not support the idea of “?” or am I doing something wrong?

Answer 1

From the fine PG::Connection manual:

- (PG::Result) exec(sql[, params, result_format ])
- (Object) exec(sql[, params, result_format ]) {|pg_result| ... }
[…]
PostgreSQL bind parameters are represented as $1, $1, $2, etc., inside the SQL query. The 0th element of the params array is bound to $1, the 1st element is bound to $2, etc. nil is treated as NULL.

So you want to use numbered placeholders with PostgreSQL:

def existsCheck( db, id )
    temp = db.exec( 'SELECT 1 WHERE EXISTS(
        SELECT 1
        FROM Products
        WHERE promoID = $1
    ) ', [id] ).to_a.length > 0
    # You'll also need to .to_a the result before you can
    # treat it as an array...
end