Is there a way to make this look a little better?
conn.exec 'select attr1, attr2, attr3, attr4, attr5, attr6, attr7 ' +
'from table1, table2, table3, etc, etc, etc, etc, etc, ' +
'where etc etc etc etc etc etc etc etc etc etc etc etc etc'
Like, is there a way to imply concatenation?
This question is related to
ruby
code-formatting
The answer is
There are pieces to this answer that helped me get what I needed (easy multi-line concatenation WITHOUT extra whitespace), but since none of the actual answers had it, I'm compiling them here:
str = 'this is a multi-line string'\
' using implicit concatenation'\
' to prevent spare \n\'s'
=> "this is a multi-line string using implicit concatenation to eliminate spare
\\n's"
As a bonus, here's a version using funny HEREDOC syntax (via this link):
p <<END_SQL.gsub(/\s+/, " ").strip
SELECT * FROM users
ORDER BY users.id DESC
END_SQL
# >> "SELECT * FROM users ORDER BY users.id DESC"
The latter would mostly be for situations that required more flexibility in the processing. I personally don't like it, it puts the processing in a weird place w.r.t. the string (i.e., in front of it, but using instance methods that usually come afterward), but it's there. Note that if you are indenting the last END_SQL identifier (which is common, since this is probably inside a function or module), you will need to use the hyphenated syntax (that is, p <<-END_SQL instead of p <<END_SQL). Otherwise, the indenting whitespace causes the identifier to be interpreted as a continuation of the string.
This doesn't save much typing, but it looks nicer than using + signs, to me.
Also (I say in an edit, several years later), if you're using Ruby 2.3+, the operator <<~ is also available, which removes extra indentation from the final string. You should be able to remove the .gsub invocation, in that case (although it might depend on both the starting indentation and your final needs).
EDIT: Adding one more:
p %{
SELECT * FROM users
ORDER BY users.id DESC
}.gsub(/\s+/, " ").strip
# >> "SELECT * FROM users ORDER BY users.id DESC"
conn.exec [
"select attr1, attr2, attr3, ...",
"from table1, table2, table3, ...",
"where ..."
].join(' ')
This suggestion has the advantage over here-documents and long strings that auto-indenters can indent each part of the string appropriately. But it comes at an efficiency cost.
conn.exec = <<eos
select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc
eos
The Ruby-way (TM) since Ruby 2.3: Use the squiggly HEREDOC <<~
to define a multi-line string with newlines and proper indentation:
conn.exec <<~EOS
select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc
where etc etc etc etc etc etc etc etc etc etc etc etc etc
EOS
# -> "select...\nfrom...\nwhere..."
If proper indentation is not a concern, then single and double quotes can span multiple lines in Ruby:
conn.exec "select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc"
# -> "select...\n from...\n where..."
If single or double quotes are cumbersome because that would need lots of escaping, then the percent string literal notation % is the most flexible solution:
conn.exec %(select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc
where (ProductLine = 'R' OR ProductLine = "S") AND Country = "...")
# -> "select...\n from...\n where..."
If the aim is to avoid the newlines (which both the squiggly HEREDOC, quotes and the percent string literal will cause), then a line continuation can be used by putting a backslash \ as the last non-whitespace character in a line. This will continue the line and will cause Ruby to concatenate the Strings back to back (watch out for those spaces inside the quoted string):
conn.exec 'select attr1, attr2, attr3, attr4, attr5, attr6, attr7 ' \
'from table1, table2, table3, etc, etc, etc, etc, etc, ' \
'where etc etc etc etc etc etc etc etc etc etc etc etc etc'
# -> "select...from...where..."
If you use Rails, then String.squish will strip the string of leading and trailing space and collapse all consecutive whitespaces (newlines, tabs, and all) into a single space:
conn.exec "select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc".squish
# -> "select...attr7 from...etc, where..."
More details:
Ruby HEREDOC Syntax
The Here Document Notation for Strings is a way to designate long blocks of text inline in code. It is started by << followed by a user-defined String (the End of String terminator). All following lines are concatenated until the End of String terminator is found at the very beginning of a line:
puts <<HEREDOC
Text Text Text Text
Bla Bla
HEREDOC
# -> "Text Text Text Text\nBlaBla"
The End of String terminator can be chosen freely, but it is common to use something like "EOS" (End of String) or something that matches the domain of the String such as "SQL".
HEREDOC supports interpolation by default or when the EOS terminator is double quoted:
price = 10
print <<"EOS" # comments can be put here
1.) The price is #{price}.
EOS
# -> "1.) The price is 10."
Interpolation can be disabled if the EOS terminator is single quoted:
print <<'EOS' # Disabled interpolation
3.) The price is #{price}.
EOS
# -> "3.) The price is #{price}."
One important restriction of the <<HEREDOC is that the End of String terminator needs to be at the beginning of the line:
puts <<EOS
def foo
print "foo"
end
EOS
EOS
#-> "....def foo\n......print "foo"\n....end\n..EOS"
To get around this, the <<- syntax was created. It allows the EOS terminator to be indented to make the code look nicer. The lines between the <<- and EOS terminator are still used in their full extend including all indentation:
def printExample
puts <<-EOS # Use <<- to indent End of String terminator
def foo
print "foo"
end
EOS
end
# -> "....def foo\n......print "foo"\n....end"
Since Ruby 2.3, we now have the squiggly HEREDOC <<~ removes leading whitespace:
puts <<~EOS # Use the squiggly HEREDOC <<~ to remove leading whitespace (since Ruby 2.3!)
def foo
print "foo"
end
EOS
# -> "def foo\n..print "foo"\nend"
Empty lines and lines which only contains tabs and space are ignored by <<~
puts <<~EOS.inspect
Hello
World!
EOS
#-> "Hello\n..World!"
If both tabs and spaces are used, tabs are considered as equal to 8 spaces. If the least-indented line is in the middle of a tab, this tab is not removed.
puts <<~EOS.inspect
<tab>One Tab
<space><space>Two Spaces
EOS
# -> "\tOne Tab\nTwoSpaces"
HEREDOC can do some crazy stuff such as executing commands using backticks:
puts <<`EOC`
echo #{price}
echo #{price * 2}
EOC
HEREDOC String definitions can be "stacked", which means that the first EOS terminator (EOSFOO below) will end the first string and start the second (EOSBAR below):
print <<EOSFOO, <<EOSBAR # you can stack them
I said foo.
EOSFOO
I said bar.
EOSBAR
I don't think anybody would ever use it as such, but the <<EOS is really just a string literal and can be put whereever a string can normally be put:
def func(a,b,c)
puts a
puts b
puts c
end
func(<<THIS, 23, <<THAT)
Here's a line
or two.
THIS
and here's another.
THAT
If you don't have Ruby 2.3, but Rails >= 3.0 then you can use String.strip_heredoc which does the same as <<~
# File activesupport/lib/active_support/core_ext/string/strip.rb, line 22
class String
def strip_heredoc
gsub(/^#{scan(/^[ \t]*(?=\S)/).min}/, "".freeze)
end
end
puts <<-USAGE.strip_heredoc # If no Ruby 2.3, but Rails >= 3.0
This command does such and such.
Supported options are:
-h This message
...
USAGE
Troubleshooting
If you see errors when Ruby parses your file, then it is most likely that you either have extra leading or trailing spaces with a HEREDOC or extra trailing spaces with a squiggly HEREDOC. For example:
What you see:
database_yml = <<~EOS
production:
database: #{fetch(:user)}
adapter: postgresql
pool: 5
timeout: 5000
EOS
What Ruby tells you:
SyntaxError: .../sample.rb:xx: can't find string "EOS" anywhere before EOF
...sample.rb:xx: syntax error, unexpected end-of-input, expecting `end'
What is at fault:
Spot the extra spaces after the terminating EOS.
Percent String Literals
See RubyDoc for how to use the percentage sign followed by a string in a parentheses pair such as a %(...), %[...], %{...}, etc. or a pair of any non-alphanumeric character such as %+...+
Last Words
Last, to get the answer to the original question "Is there a way to imply concatenation?" answered: Ruby always implies concatenation if two strings (single and double quoted) are found back to back:
puts "select..." 'from table...' "where..."
# -> "select...from table...where..."
The caveat is that this does not work across line-breaks, because Ruby is interpreting an end of statement and the consequitive line of just strings alone on a line doesn't do anything.
Sometimes is worth to remove new line characters \n like:
conn.exec <<-eos.squish
select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc
eos
Like you, I was also looking for a solution which does not include newlines. (While they may be safe in SQL, they're not safe in my case and I have a large block of text to deal with)
This is arguably just as ugly, but you can backslash-escape newlines in a heredoc to omit them from the resulting string:
conn.exec <<~END_OF_INPUT
select attr1, attr2, attr3, attr4, attr5, attr6, attr7 \
from table1, table2, table3, etc, etc, etc, etc, etc, \
where etc etc etc etc etc etc etc etc etc etc etc etc etc
END_OF_INPUT
Note that you cannot due this without interpolation (I.E. <<~'END_OF_INPUT') so be careful. #{expressions} will be evaluated here, whereas they will not in your original code. A. Wilson's answer may be better for that reason.
conn.exec 'select attr1, attr2, attr3, attr4, attr5, attr6, attr7 ' <<
'from table1, table2, table3, etc, etc, etc, etc, etc, ' <<
'where etc etc etc etc etc etc etc etc etc etc etc etc etc'
<< is the concatenation operator for strings
You can also use double quotes
x = """
this is
a multiline
string
"""
2.3.3 :012 > x
=> "\nthis is\na multiline\nstring\n"
If needed to remove line breaks "\n" use backslash "\" at the end of each line
There are multiple syntaxes for multi-line strings as you've already read. My favorite is Perl-style:
conn.exec %q{select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc}
The multi-line string starts with %q, followed by a {, [ or (, and then terminated by the corresponding reversed character. %q does not allow interpolation; %Q does so you can write things like this:
conn.exec %Q{select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from #{table_names},
where etc etc etc etc etc etc etc etc etc etc etc etc etc}
I actually have no idea how these kinds of multi-line strings are called so let's just call them Perl multilines.
Note however that whether you use Perl multilines or heredocs as Mark and Peter have suggested, you'll end up with potentially unnecessary whitespaces. Both in my examples and their examples, the "from" and "where" lines contain leading whitespaces because of their indentation in the code. If this whitespace is not desired then you must use concatenated strings as you are doing now.
In ruby 2.0 you can now just use %
For example:
SQL = %{
SELECT user, name
FROM users
WHERE users.id = #{var}
LIMIT #{var2}
}
To avoid closing the parentheses for each line you can simply use double quotes with a backslash to escape the newline:
"select attr1, attr2, attr3, attr4, attr5, attr6, attr7 \
from table1, table2, table3, etc, etc, etc, etc, etc, \
where etc etc etc etc etc etc etc etc etc etc etc etc etc"
Recently with the new features in Ruby 2.3 the new squiggly HEREDOC will let you write our multiline strings in a nice manner with a minimal change so using this combined with the .squish (if you are using rails) will let you write multiline in a nice way!
in case of just using ruby, you can do a <<~SQL.split.join(" ") which is almost the same
[1] pry(main)> <<~SQL.squish
[1] pry(main)* select attr1, attr2, attr3, attr4, attr5, attr6, attr7
[1] pry(main)* from table1, table2, table3, etc, etc, etc, etc, etc,
[1] pry(main)* where etc etc etc etc etc etc etc etc etc etc etc etc etc
[1] pry(main)* SQL
=> "select attr1, attr2, attr3, attr4, attr5, attr6, attr7 from table1, table2, table3, etc, etc, etc, etc, etc, where etc etc etc etc etc etc etc etc etc etc etc etc etc"
ref: https://infinum.co/the-capsized-eight/multiline-strings-ruby-2-3-0-the-squiggly-heredoc
Other options:
#multi line string
multiline_string = <<EOM
This is a very long string
that contains interpolation
like #{4 + 5} \n\n
EOM
puts multiline_string
#another option for multiline string
message = <<-EOF
asdfasdfsador #{2+2} this month.
asdfadsfasdfadsfad.
EOF
puts message
If you do mind extra spaces and newlines, you can use
conn.exec %w{select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc} * ' '
(use %W for interpolated strings)
Elegant Answer Today:
<<~TEXT
Hi #{user.name},
Thanks for raising the flag, we're always happy to help you.
Your issue will be resolved within 2 hours.
Please be patient!
Thanks again,
Team #{user.organization.name}
TEXT
Theres a difference in <<-TEXT and <<~TEXT, former retains the spacing inside block and latter doesn't.
There are other options as well. Like concatenation etc. but this one makes more sense in general.
If I am wrong here, let me know how...
Yes, if you don't mind the extra newlines being inserted:
conn.exec 'select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc'
Alternatively you can use a heredoc:
conn.exec <<-eos
select attr1, attr2, attr3, attr4, attr5, attr6, attr7
from table1, table2, table3, etc, etc, etc, etc, etc,
where etc etc etc etc etc etc etc etc etc etc etc etc etc
eos
Source: Stackoverflow.com