JSON Patch

Patch json documents. This set of functions presents an R-ish interface to all the json patch verbs (add, remove, copy, replace, move, and test). It does not implement the json-format patch (i.e., a patch represented itself as a json document). The primary use case here is to allow expressing modifications to a json document from R without having to deserialise the document into R's data structures, so that a "json -> R -> json" roundtrip can be done losslessly, with modification in R.

json_patch_remove(json, path)

json_patch_replace(json, path, value)

json_patch_add(json, path, value)

json_patch_copy(json, from, path)

json_patch_move(json, from, path)

json_patch_test(json, path, value)

Arguments

json

The json document to work with

path

The patch to modify (or for json_patch_test, to test)

value

The value to add (json_patch_add), replace an existing value with (json_patch_replace) or test (json_patch_test)

from

The source value for json_patch_move and json_patch_copy

Value

The modified json document (in parsed form) or throws if impossible

Details

This interface is designed to play nicely with R's piping operator, see examples.

The verbs are:

Add (json_patch_add)

Adds a value to an object or inserts it into an array. In the case of an array, the value is inserted before the given index. The - character can be used instead of an index to insert at the end of an array. Note that the first element has index 0 (not 1).

Remove (json_patch_remove)

Removes a value from an object or array.

Replace (json_patch_replace)

Replaces a value. Equivalent to a remove followed by an add.

Copy (json_patch_copy)

Copies a value from one location to another within the JSON document.

Move (json_patch_move)

Moves a value from one location to the other.

Test (json_patch_test)

Tests that the specified value is set in the document. If the test fails, then an error is thrown, so can be used within a pipeline to prevent a patch applying.

See also

The json patch specification for more details, at https://jsonpatch.com/

Examples

# The example doc used in https://jsonpatch.com/
doc <- tinyjson::from_json('{
  "biscuits": [
    { "name": "Digestive" },
    { "name": "Choco Leibniz" }
   ]
}')

# add
tinyjson::json_patch_add(doc, "/biscuits/1", '{"name": "Ginger Nut"}') |>
  tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Digestive\"},{\"name\":\"Ginger Nut\"},{\"name\":\"Choco Leibniz\"}]}"

# remove
tinyjson::json_patch_remove(doc, "/biscuits") |> tinyjson::to_json()
#> [1] "{}"
tinyjson::json_patch_remove(doc, "/biscuits/0") |> tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Choco Leibniz\"}]}"

# replace (note the extra quotes here, the 'value' gets parsed as
# json and is not an R string)
tinyjson::json_patch_replace(
  doc, "/biscuits/0/name", '"Chocolate Digestive"') |> tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Chocolate Digestive\"},{\"name\":\"Choco Leibniz\"}]}"

# copy
tinyjson::json_patch_copy(doc, "/biscuits/0", "/best_biscuit") |>
  tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Digestive\"},{\"name\":\"Choco Leibniz\"}],\"best_biscuit\":{\"name\":\"Digestive\"}}"

# move
tinyjson::json_patch_copy(doc, "/biscuits", "/cookies") |>
  tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Digestive\"},{\"name\":\"Choco Leibniz\"}],\"cookies\":[{\"name\":\"Digestive\"},{\"name\":\"Choco Leibniz\"}]}"

# test
tinyjson::json_patch_test(doc, "/biscuits/1/name", '"Choco Leibniz"') |>
  tinyjson::to_json()
#> [1] "{\"biscuits\":[{\"name\":\"Digestive\"},{\"name\":\"Choco Leibniz\"}]}"