From the rails postgresql_adapter.rb. I get what it's trying to do, I just don't get how it happens. It's really to do with the <<-SQL that I'm lost.
exec_query(<<-SQL, 'SCHEMA', binds).rows.first[0].to_i > 0
SELECT COUNT(*)
FROM pg_tables
WHERE tablename = $1
#{schema ? "AND schemaname = $2" : ''}
SQL
I've seen code before where you could say:
blah = <<-X
some
lines
of
test
X
But I've never seen this done within the argument to a function call. I'm really confused by this. Can someone explain to me what exactly is going on here?
You can use a heredoc-marker (like <<-SQL
in your example) anywhere (or even multiple times) in a line and the heredoc will then start on the following line and continue until the end-marker is met (in case of multiple markers, the (n+1)th heredoc will start after the nth end-marker and continue up to the (n+1)th end-marker). The content of each heredoc will then be inserted at the place where the corresponding marker was used.
So
foo(<<BAR, 42)
bar
BAR
is the same as
foo("bar\n", 42)
and
foo(<<BAR, <<BAZ)
bar
BAR
baz
BAZ
is the same as
foo("bar\n", "baz\n")
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