2600Hz JSON

Manipulating JSON objects in Erlang.

Accessors

Getters

The kz_json module provides a generic accessor, get_value(Path, JObj[, Default]) that will return the value at Path ('undefined' or Default if missing).

There are also a number of accessors that will make sure the value retrieved is of a certain type; otherwise the Default is used. Functions like get_ne_binary_value will make sure the Value is a non-empty binary, for instance.

Another accessor is get_first_defined(Paths, JObj[, Default]) which takes a list of paths to search, returning the first non-'undefined' value found iterating through Paths; otherwise 'undefined' or Default is returned.

  • get_keys(JObj): returns the top-level keys of the JObj.
  • get_values(JObj): will return a tuple {Values, Keys} from the object (similar to lists:unzip/2).
  • values(JObj): returns just the top-level Values of the object.
  • new(): returns an empty JSON object.

Setters

  • set_value(Path, Value, JObj) will put Value at Path (including creating nested objects as necessary).
  • set_values([{Path, Value}], JObj) will put Values at Paths (including creating nested objects as necessary).
  • insert_value(Path, Value, JObj) will only put Value at Path if there isn’t a value there already.
  • insert_values([{Path, Value}], JObj) will only put Value at Path if there isn’t a value there already.

Deleting keys

  • delete_key(Path, JObj[, 'prune' | 'no_prune']): will delete the value at Path from the JObj. You can optionally prune the resulting empty object ('no_prune' is the default).
  • delete_keys(Paths, JObj): will delete Paths using 'no_prune'. Use prune_keys(Paths, JObj) if you want empty objects pruned.

Note that set_value(Path, 'null', JObj) is equivalent to delete_key(Path, JObj).

Predicates

Several predicates exist that will return booleans.

  • is_true(Path, JObj[, Default]): returns if the value at Path is “true” in some form (atom, list, binary). is_false exists as well for “false”.
  • is_defined(Path, JObj): Returns if the value at Path is not 'undefined'.
  • is_empty(JObj): returns true if JObj is the empty JSON object ({[]} currently but could be #{} if the switch to maps is made).
  • is_json_object(JObj), are_json_objects(JObjs): Superficial check for the internal JSON structure. Use is_valid_json_object(JObj) to recurse into the data structure.
  • is_json_term(Term): returns if the Term is a JSON-able term. Terms like pid(), reference(), and such have no parallel in JSON and are thus considered to not be JSON terms.
  • are_equal(JObj1, JObj2): compares two objects for equality, irrespective of how the underlying ordering of keys.

Converters

Away from JSON objects

  • to_proplist(JObj): Returns the top-level object as a proplist instead (nested objects remain objects).
  • to_map(JObj): Returns a map representation of the object
  • recursive_to_proplist(JObj): Converts nested objects to proplists as well

To JSON objects

  • from_list(Proplist): Top-level change from proplist to object
  • from_map(Map): Converts map back to JSON object data structure
  • from_list_recursive(Proplist): Equivalent to from_list_recursive/2 with default option: #{ascii_list_enforced => 'true', invalid_as_null => 'true'}
  • from_list_recursive(Proplist, #{}=Options): Converts nested proplists to objects as well. Options are:
    • ascii_list_enforced: If the value of a proplist item is list and all of the elements are ASCII characters, convert the value to binary. This also converts empty list [] to binary. If you are sure that you don’t have any string value, but expect and empty list as value, set this option to false to not convert the empty list to binary
    • invalid_as_null: If the value of a proplist item is not any of list(), binary(), atom(), integer(), float(), kz_time:date(), kz_time:datetime(), kz_json:object() or kz_term:proplist() then set the value to null, otherwise throw {'error', kz_term:ne_binary()}

Merging Objects

You can merge two (or more) objects together and specify which objects’ value will be used when there are conflicting keys.

  • merge([JObj1, JObj2,...]): Defaults to using the merge_right strategy where the object on the “right” will have its value used when both objects have a value at a given key path.
  • merge(Strategy, JObjs): Choose a strategy, either fun kz_json:merge_right/2 or fun kz_json:merge_left/2 (or define your own), and apply it to the list of objects.

Both merge_left/2 and merge_right/2 will keep the left or right empty objects (respectively) when they exist at a given key path if the other value is also an object (empty or not). To override this behavior and always recursively merge the values when both are objects, specify 'recursive' => 'true' in the Options map passed in merge(JObjs, Options), merge(JObj1, JObj2, Options), merge(Strategy, JObjs, Options), or merge(JObj1, JObj2, Options), as arg 4 to merge/4, or as arg 5 to merge/5.

Handling null

Sometimes it is beneficial to include the null atom as a value (for downstream processing perhaps) versus triggering a delete_key equivalent.

set_value and merge can take an optional map #{'keep_null' => 'true'} to ensure null is kept in the resulting data structure.

List-like operations

JSON objects are iterable and kz_json has equivalents to the lists module for filter/{2,3}, filtermap/2, map/2, fold{l,r}/3, foreach/2, all/2, and any/2 among others.

Another of note is find(Path, JObjs[, Default]) which searchs a list of JSON objects for a key path. There is also a find_first_defind(Paths, JObjs[, Default]) which will find(Path, JObjs), continuing to the next Path if 'undefined' is returned.

There is also a find_value(Path, Value, JObjs[, Default]) which will find the first JObj in the list that has Value at Path.

Lifting common JSON properties

Basic usage

kz_json:lift_common_properties([JObj1, JObj2]) ->
    {CommonJObj, [UniqueJObj1, UniqueJObj2]}.

All key/value pairs common to each JObj in the list will be collected into CommonJObj and removed from each JObj.

Blacklists

Sometimes you know there are keys that shouldn’t be lifted (like leg-only variables on endpoints vs channel variables):

kz_json:lift_common_properties([JObj1, JObj2,...], [Key1, Path2]) ->
    {CommonJObj, [UniqueJObj1, UniqueJObj2,...]}.

This will not allow Key1 and Path2 to be in CommonJObj and will remain in the objects that have it set. Note that the blacklist can be keys (<<"key">>) or paths ([<<"key">>, <<"subkey">>]).

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