问题
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?
回答1:
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.
EDIT: Adding one more:
p %{
SELECT * FROM users
ORDER BY users.id DESC
}.gsub(/\s+/, " ").strip
# >> "SELECT * FROM users ORDER BY users.id DESC"
回答2:
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
回答3:
In ruby 2.0 you can now just use %
For example:
SQL = %{
SELECT user, name
FROM users
WHERE users.id = #{var}
LIMIT #{var2}
}
回答4:
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.
回答5:
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
回答6:
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
回答7:
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
回答8:
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
回答9:
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 will let you write multiline in a nice way!
[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
回答10:
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
回答11:
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)
回答12:
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"
回答13:
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.
来源：https://stackoverflow.com/questions/2337510/ruby-can-i-write-multi-line-string-with-no-concatenation