Lua sqlite Select statement

Question

I have the following code to create a database table if it does not already exist then check if the current user is in the database or not. I do this by selecting the user with id equal to their device id. The code right now should print hello world and then go to forms. However when I run the code nothing happens, no errors and no print statement. Any ideas why this might be happening?

local tablesetup = [[CREATE TABLE IF NOT EXISTS User (id VARCHAR(255) PRIMARY KEY, name);]]
    db:exec(tablesetup)

    --Check if the user is in the database already
    for row in db:nrows("SELECT * FROM User WHERE id = " .. "'" .. system.getInfo("deviceID") .. "'") do
        print("hello")
        if(row.id == nil) then
            print("world")
            storyboard.gotoScene("forms")
        end
    end

Nicol Bolas · Accepted Answer · 2012-05-27 20:02:07Z

3

nrows returns all of the rows produced by a query. If no rows were produced in a query (because, for example, the item(s) you were looking for was not found), then the loop will not start. Because there was no row that matched the query.

If you're looking to detect if a query succeeded or not, then you'll need to actually check that.

Also, please stop building queries with string concatenation. Learn how to use prepared statements with proper value binding. It's much cleaner and has the benefit of not leaving you open to SQL injection attacks.

answered May 27, 2012 at 20:02

Nicol Bolas

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3 Comments

ewein Over a year ago

well what I am trying to do is check if the user is in the database or not. So if they are not in the database the loop will just be skipped?

Nicol Bolas Over a year ago

@ewein: Yes. Just like if you loop over an empty list, you don't go into the loop.

engineerX Over a year ago

How do you "actually check that"? lua.sqlite.org/index.cgi/doc/tip/doc/lsqlite3.wiki there is no method which obviously tells you whether the result set is empty.

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