Getting Started | API | Elements | Actions | Validators | Handlers | Configuration Options | Advanced Guides | Troubleshooting | About

Config Handler

The config handler controls how the configuration settings are loaded. This is probably not something that's likely to get changed.

Behavior Functions

init(Config, State)

Initialize the handler

• /Return Value/ - {ok, NewState}

finish(Config, State)

Clean up the handler

• /Return Value/ - {ok, NewState}

get_value(Key, DefaultValue, Config, State)

Search the configuration for the key and return the value

• Key - The configuration key to find

• DefaultValue - If the Key is not found, return the provided value

• /Return Value/ - The value of the found key

get_values(Key, DefaultValue, Config, State)

Search the configuration and return a list of found values, if the configuration system you're using can return multiple values for a single key.

• Key - The configuration key to find

• DefaultValue - If the Key is not found, return the provided value

• /Return Value/ - The values of the found key

Example

-module (default_config_handler).
-include_lib ("wf.hrl").
-behaviour (config_handler).
-export ([
    init/2,
    finish/2,
    get_value/4,
    get_values/4
]).

init(_Config, _State) ->
    {ok, []}.

finish(_Config, _State) ->
    {ok, []}.

get_value(Key, DefaultValue, Config, State) ->
    case get_values(Key, [DefaultValue], Config, State) of
        [Value] ->
            Value;
        Values ->
            error_logger:error_msg("Too many matching config values for key: ~p~n", [Key]),
            throw({nitrogen_error, too_many_matching_values, Key, Values})
    end.

get_values(Key, DefaultValue, _Config, _State) ->
    case application:get_env(nitrogen, Key) of
        {ok, Value} ->
            [Value];
        undefined ->
            DefaultValue
    end.

See Also

• Handler Overview

• API: Configuration