Rails load YAML to hash and reference by symbol

问题:

I am loading a YAML file in Rails 3.0.9 like this:

APP_CONFIG = YAML.load(File.read(File.expand_path('../app.yml', __FILE__)))

It loads the all of the contents like hierarchical hashes, no problem. The part I don't like is the fact that the hashes can only be accessed with single or double quotes but not a symbol.

APP_CONFIG['mailer']['username']  # works fine
APP_CONFIG[:mailer][:username]    # doesn't

Any thoughts?

回答1:

Try using the HashWithIndifferentAccess like

APP_CONFIG = HashWithIndifferentAccess.new(YAML.load(File.read(File.expand_path('../app.yml', __FILE__))))

回答2:

An alternative solution is to have the keys which you wish to access as a symbol prepended with a colon. For example:

default: &default
  :symbol: "Accessed via a symbol only"
  string: "Accessed via a string only"

development:
  <<: *default

test:
  <<: *default

production:
  <<: *default

Later you can then access these like so:

APP_CONFIG[:symbol]
APP_CONFIG['string']

Note that I am using YAML::ENGINE.yamler = "syck". Not sure if this works with psych. (Psych definitely won't support key merging as I showed in the example though.)

About using HashWithIndifferentAccess: using it has the side effect of creating duplicate keys: one for symbol access and one for string access. This might be nefarious if you pass around YAML data as arrays. Be aware of this if you go with that solution.

回答3:

If you are working in Ruby on Rails, You might want to take a look at symbolize_keys(), which does exactly what the OP asked for. If the hash is deep,you can use deep_symbolize_keys(). Using this approach, the answer is

APP_CONFIG = YAML.load(File.read(File.expand_path('../app.yml', __FILE__))).deep_symbolize_keys

回答4:

This is the same from the selected answer, but with a better syntax:

YAML.load(File.read(file_path)).with_indifferent_access 

回答5:

There is another potential answer I discovered while digging around.

You can forgo HashWithIndifferentAccess.new by instead adding this to the top of your YAML files:

--- !map:HashWithIndifferentAccess

then simply YAML.load like normal. The only trick is that rails needs to already be loaded if you are doing this in your environment for use in initializers, etc. (like I am).

回答6:

1. Rails has a special method to symbolize keys.
2. You can use load_file method and get rid of File.read
3. Not sure if you need expand_path also, the default directory is rails root.

I'd write it that simple:

YAML::load_file('app.yml').symbolize_keys

回答7:

You are probably used to the params hash in Rails, which is actually a HashWithIndifferentAccess rather than a standard ruby Hash object. This allows you to use either strings like 'action' or symbols like :action to access the contents.

With a HashWithIndifferentAccess, you will get the same results regardless of what you use, but keep in mind this only works on HashWithIndifferentAccess objects.

So to make this work with YAML, you'll have to load the result of YAML.load into a HashWithIndifferentAccess, like so:

APP_CONFIG = HashWithIndifferentAccess.new(   YAML.load(File.read(File.expand_path('../app.yml', __FILE__)))   )

回答8:

If you're using pure Ruby (i.e. no Rails), you could intermediately change to JSON format. The JSON lib's parse method can symbolize keys.

http://ruby-doc.org/stdlib-2.0.0/libdoc/json/rdoc/JSON.html#method-i-parse

Here's what I mean:

JSON.parse(JSON.dump(YAML.load_file(File.expand_path('../app.yml', __FILE__))), symbolize_names: true)

Note: This adds overhead of conversion to and from json.

回答9:

I usually don't use HashWithIndifferentAccess just to avoid confusion and prevent inconsistencies in the way that it is accessed, so what I would do instead is tack on a .deep_symbolize_keys to get the whole thing in symbol key form.