Ruby/Rails: Parsing and inserting partials into text

Question

Suppose I have a body of text (string) like this:

str = 'This is some text. {insertion_1} And this is also some text. {insertion_2}'

The contents of the two curly braces represent a model ( Insertion ) and its ID. The ultimate goal is to parse the string, and replace the curly braced "insertions" with an insertion partial. The insertion partial will simply be a line or two of HTML.

If the insertions were static I could do something like str.gsub!(/\\{insertion_\\d*\\}/, 'some content') , but I need to parse the insertions one-by-one, to insert the appropriate data. Can anyone suggest a best practice for handling a situation like this?

EDIT: I should have mentioned, this is for a WYSIWYG. The end user selects from a list of "insertions" and once selected, it adds the appropriate {insertion_id} placeholder into the body of their post, which will be parsed out later to insert the right content.

Answer 1

You can use regexp captures and gsub with a block to accomplish what you want, like this:

str = 'This is some text. {insertion_1} And this is also some text. {insertion_2}'

replacements = {
  1 => 'HELLO',
  2 => 'WORLD',
}

str.gsub(/\{insertion_(\d*)\}/) {
  id = $1.to_i
  replacements[id]
}
# => "This is some text. HELLO And this is also some text. WORLD" 

Just replace the block body with whatever you need to do. :)

(Sidenote: \\d+ is a better choice than \\d* for matching numbers.)

Answer 2

You could... use partials, and provide data. Those may also be rendered to a string using render_to_string .

You could use raw Erb, which can parse strings; doesn't need to be a template on disk.

You could use normal string interpolation:

t1 = "ohai"
p "This is some text. #{t1}, kthxbai."

Answer 3

An alternative method is to use the %s in your string. Here's an example.

names = %w(chris john robert mike)
welcome = "Hello %s, %s would like to show you around. %s and %s are waiting in the other room" % names
# => "Hello chris, john would like to show you around. robert and mike are waiting in the other room"

Answer 4

If you need something bigger and more versatile than just plain old ruby style "foo #{bar} baz" you might want to look into liquid .

It basically works like erb, but you use {{ some_variable }} for your tags instead of <%= some_variable %> . It also has support for loops and custom tags and all sorts of nifty stuff.