I want to check if a record already exist in my database. In my function i have this code:
mailcode = params[:q] check = User.where("custom_mailcode = 'mailcode'").first Now i'm in trouble with the if statement. I think to do something like that:
if check == nil doing something else doing something end But it doesn't work because check is never nil. How can i fix that?
You could try
User.where("custom_mailcode = 'mailcode'").any?
If you intend to use the user record you can instead use find_by
user = User.find_by(custom_mailcode: params[:q]) # User / nil if user # ... else # ... end find_by unlike where returns the first record or nil.
If you do not plan on using the database values than use .any? it will issue a COUNT SQL query which is slightly faster and uses less memory.
# ActiveRecord only loads a boolean into memory if User.where(custom_mailcode: params[:q]).any? # ... else # ... end You could do
if check.present? ... else ... end 
.first on a relation will either return nil or the first object, so while this more readable, how does this fix the question?You can do the following:
if check = User.where(custom_mailcode: params[:q]).first p check else doing something else end Ha I see the error, the error is not in your check, but in your where-clause. You are always looking for a fixed string called mailcode, not the value of the variable. The easiest fix is just to write the where differently:
check = User.where(custom_mailcode: params[:q]).first Or use proper string interpolation
check = User.where("custom_mailcode = '#{mailcode}'").first which you should avoid, because this makes your application vulnerable to SQL injection attacks; just showing the proper way to do string interpolation.
And then you just test
if check == nil But I personally prefer check.nil?.
find_by(ustom_mailcode: params[:q]) instead of .where(custom_mailcode: params[:q]).first the latter is just bad style.any? or count which issues a count query.where-first combination very readable, and it allows to combine various where clauses, as you usually do, and it results in the same query as the find_by. So imho it is just a matter of personal taste to use either one. But it is a good suggestion.I assume you want to modify or read the user if it's found. That can be accomplished like this:
mailcode = params[:q] user = User.find_by(custom_mailcode: mailcode) if user # do something with the user else # backup logic end Or, as is often needed, you may want to create the object, if it's not already found. There's a find_or_create_by shorthand for that purpose:
mailcode = params[:q] user = User.find_or_create_by(custom_mailcode: mailcode) user.update(meaning_of_life: 42) 
.firstwould returnnilso it should just work.where(...).firstis typically done viafind_by(...).