Jsonpatch

An implementation of RFC 6902 in pure Elixir.

Features:

• Creating a patch by comparing to maps and lists
• Apply patches to maps and lists - supports operations:
  • add
  • replace
  • remove
  • copy
  • move
  • test
• Escaping of "/" (by "~1") and "~" (by "~0")
• Allow usage of - for appending things to list (Add and Copy operation)
• Smart list diffing with object_hash for efficient patches on collections with unique identifiers

Getting started

Installation

The package can be installed by adding jsonpatch to your list of dependencies in mix.exs:

def deps do
  [
    {:jsonpatch, "~> 2.2"}
  ]
end

The docs can be found at https://hexdocs.pm/jsonpatch.

Create a diff

iex> source = %{"name" => "Bob", "married" => false, "hobbies" => ["Sport", "Elixir", "Football"]}
iex> destination = %{"name" => "Bob", "married" => true, "hobbies" => ["Elixir!"], "age" => 33}
iex> Jsonpatch.diff(source, destination)
[
  %{path: "/married", value: true, op: "replace"},
  %{path: "/hobbies/2", op: "remove"},
  %{path: "/hobbies/1", op: "remove"},
  %{path: "/hobbies/0", value: "Elixir!", op: "replace"},
  %{path: "/age", value: 33, op: "add"}
]

Smart List Diffing with object_hash

Use object_hash to generate efficient patches for lists of objects with unique identifiers, producing minimal operations instead of cascading replacements.

iex> original = [
  %{id: 1, name: "Alice"},
  %{id: 2, name: "Bob"}
]
iex> updated = [
  %{id: 99, name: "New"},
  %{id: 1, name: "Alice"},
  %{id: 2, name: "Bob"}
]

# Traditional pairwise diff - multiple replace operations
# >> Jsonpatch.diff(original, updated)
[
  %{op: "add", path: "/2", value: %{id: 2, name: "Bob"}}
  %{op: "replace", path: "/0", value: %{id: 99, name: "New"}},
  %{op: "replace", path: "/1", value: %{id: 1, name: "Alice"}},
]

# With object_hash - single add operation
iex> Jsonpatch.diff(original, updated, object_hash: fn %{id: id} -> id end)
[
  %{op: "add", path: "/0", value: %{id: 99, name: "New"}}
]

Apply patches

iex> patch = [
  %{op: "add", path: "/age", value: 33},
  %{op: "replace", path: "/hobbies/0", value: "Elixir!"},
  %{op: "replace", path: "/married", value: true},
  %{op: "remove", path: "/hobbies/1"},
  %{op: "remove", path: "/hobbies/2"}
]
iex> target = %{"name" => "Bob", "married" => false, "hobbies" => ["Sport", "Elixir", "Football"]}
iex> Jsonpatch.apply_patch(patch, target)
{:ok, %{"name" => "Bob", "married" => true, "hobbies" => ["Elixir!"], "age" => 33}}

Important sources

• Official RFC 6902
• Inspiration: python-json-patch