#jwalk ##Helper module for working with Erlang Proplist, EEP18 Mochi-style aand Map representations of JSON

This work is inspired by ej, but handles map, eep-18, mochijson-style and proplist representations of JSON - the types returned by jsone or jiffy, for example. Anything good about this is probably due to the contributors and maintainers of ej, anything bad or awkward is completely my fault.

###Dependencies The source code is a single file, and there are no dependencies other than:

• Erlang 17.0 +
• Rebar3, for building

Hex package manager is used for package management.

###QuickStart

clone

$ git clone git://github.com/jr0senblum/jwalk.git

$ cd jwalk

compile

$ make compile

run tests

$ make eunit

dialyze

$ make dialyze

Erlang shell

$ make start

1> jwalk:get({"one"},#{<<"one">> => 1}).

1

##Functions Functions always take at least two parameters: a first parameter which is a tuple of elements representing a Path into a JSON Object, and a second parameter which is expected to be a valid JSON representation (map, proplist, etc.).

• jwalk:delete(Path, Object) - Removes the value at the location specified by Path from Object and returns a new structure
• jwalk:get(Path, Object), jwalk:get(Path, Object, Default) - Returns the Value at the specificed Path from Object, or undefined or Default if not found
• jwalk:set(Path, Object, Value) - Sets a Value in Object at the specified Path and returns the new structure
• jwalk:set_p(Path, Object, Value) - Sets a Value in an Object at the specified Path creating intermediate nodes as necessary and returns the new structure

###Paths Paths into JSON Objects are expressed using a tuple of Path elements, a representation of a javascript-like path: i.e., Obj.weapons.edged.distance would be expressed as {"weapons","edged","distance"}. Path elements representing JSON Member Names can be strings or binary, they will be internally converted to binary regardless.

In addition to the string/binary representations of Member Names, a Path element can be

• An integer index, or the atoms first and last, which will select an element out of a JSON Array.
• {select, {"name","value"|value}} which will select a subset of JSON objects from an Array that have a Member {"Name": "Value"|Value}
• new for set/2 and set_p/2, when the final element of a Path is the atom new, the supplied value is added to the stucture as the first element of an Array, the Array is created if necessary

Path, string elements can be binary or not

Examples follow.

###Usage Examples Weapons = [{<<"edged">>, [[{<<"type">>, <<"swords">>}, {<<"distance">>, <<"medium">>}],
[{<<"type">>, <<"bayonets">>}, {<<"distance">>, <<"medium">>}], [{<<"type">>, <<"daggers">>}, {<<"distance">>, <<"close">>}]
]
}].

then

1> jwalk:get({"edged", {select, {"distance","medium"}}},Weapons).
[[{<<"type">>,<<"swords">>},{<<"distance">>,<<"medium">>}],
[{<<"type">>,<<"bayonets">>},{<<"distance">>,<<"medium">>}]]

2> jwalk:get({"edged",{select,{"distance","medium"}},1},Weapons).
[{<<"type">>,<<"swords">>},{<<"distance">>,<<"medium">>}]

3> jwalk:get({"edged",{select,{"distance","medium"}},1,"type"},Weapons).
<<"swords">>

% setting an element ...
4> W2 = jwalk:set({"edged",3, "distance"}, Weapons, <<"very close">>).
[{<<"edged">>,
 [[{<<"type">>,<<"swords">>},{<<"distance">>,<<"medium">>}],
  [{<<"type">>,<<"bayonets">>},{<<"distance">>,<<"medium">>}],
  [{<<"type">>,<<"daggers">>},{<<"distance">>,<<"very close">>}]]}]

5> jwalk:get({"edged","distance"},W2).
[<<"medium">>,<<"medium">>,<<"very close">>]

Given a map:

Obj = #{<<"widget">> => 
        #{<<"debug">> => <<"on">>,
          <<"image">> => 
              #{<<"alignment">> => <<"center">>,
                <<"hOffset">> => 250,
                <<"name">> => <<"sun1">>,
                <<"src">> => <<"Images/Sun.png">>,
                <<"vOffset">> => 250},
          <<"keys">> => [],
          <<"text">> => 
              #{<<"alignment">> => <<"center">>,
                <<"data">> => <<"Click Here">>,
                <<"hOffset">> => 250,
                <<"name">> => <<"text1">>,
                <<"onMouseUp">> => <<"sun1.opacity = (sun1.opacity / 100) * 90;">>,
                <<"size">> => 36,
                <<"style">> => <<"bold">>,
                <<"vOffset">> => 100},
          <<"values">> => [1,2,3,4,5],
          <<"version">> => <<"1">>,
          <<"window">> => 
              #{<<"height">> => 500,
                <<"name">> => <<"main_window">>,
                <<"title">> => <<"Sample Konfabulator Widget">>,
                <<"width">> => 500}}}.

then

1> jwalk:get({"widget","debug"},Obj).
<<"on">>

2> jwalk:get({"widget","text"},Obj).
#{<<"alignment">> => <<"center">>,
  <<"data">> => <<"Click Here">>,
  <<"hOffset">> => 250,
  <<"name">> => <<"text1">>,
  <<"onMouseUp">> => <<"sun1.opacity = (sun1.opacity / 100) * 90;">>,
  <<"size">> => 36,
  <<"style">> => <<"bold">>,
  <<"vOffset">> => 100}

set_p creates intermediary nodes:

1> jwalk:set_p({"users", {select, {"name", "sebastian"}}, "location"}, #{}, <<"Germany">>).
#{<<"users">> => [#{<<"location">> => <<"Germany">>,<<"name">> => <<"sebastian">>}]}

2> jwalk:set_p({"users", {select, {"name", "sebastian"}}, "location"}, [{}],    <<"Germany">>).	[{<<"users">>,
  [[{<<"name">>,<<"sebastian">>},
        {<<"location">>,<<"Germany">>}]]}]

3> jwalk:set_p({"users", {select, {"name", "sebastian"}}, "location"}, {[]},    <<"Germany">>).
{[{<<"users">>,
  [{[{<<"name">>,<<"sebastian">>},
         {<<"location">>,<<"Germany">>}]}]}]}

4> jwalk:set_p({"users", {select, {"name", "sebastian"}}, "location"}, {struct,[]}, <<"Germany">>).
{struct,[{<<"users">>,
    [{struct,[{<<"name">>,<<"sebastian">>},
              {<<"location">>,<<"Germany">>}]}]}]}