datum-merge

datum-merge is a modern typescript library that simplifies merge and diff operations for deeply nested objects.

Source Code : https://github.com/therohk/datum-merge

NPM library : https://www.npmjs.com/package/datum-merge

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Sample Usage

Merge with default config:

import { merge, detailMerge, UpdateCode } from "datum-merge";
let changed = merge(target, source, UpdateCode.I, UpdateCode.XM, UpdateCode.B);
//same as
changed = customMerge(target, source, { 
    scalar: UpdateCode.I, 
    vector: UpdateCode.XM, 
    nested: UpdateCode.B 
});

Exact nestable config that ignores all other fields:

changed = detailMerge(target, source, {
    mykey: UpdateCode.I, 
    myarr: UpdateCode.XM, 
    anobj: UpdateCode.B,
    myobj: { myid: UpdateCode.I },
});

Deep merge with generic config patterns:

import { customMerge, MergeConfig, UpdateCode } from "datum-merge";
const conf: MergeConfig = {
    "*_id": UpdateCode.I,
    scalar: UpdateCode.B,
    field1: UpdateCode.D,
    "arr*": UpdateCode.XM,
    nested: UpdatedCode.N,
    obj1: {
        scalar: UpdateCode.B,
        vector: UpdateCode.XM,
    },
};
let diff = customMerge(target, source, conf);

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Upcoming Features

1. inline the unmaintained deep-diff library which contains serious bugs. (available)

2. support merging for top level arrays or primitives.

3. option to throw error if field datatype changes during merge.

4. project should compile in strict mode.

5. formalize config schema for deeply nested objects (for v1).

Code contributions are welcome via issues and pull requests.

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Merge Strategy

This string code describes how modifications to an attribute for a PUT/UPDATE operation should be handled. It decides whether a change to the value of the field is allowed during a merge between two entities.

Strategy Codes

The same field within a source and target object is represented by s and t respectively. Whether the strategy requires data to be present for the field, is shown by { 0=no, 1=yes, X=irrelavant }. The value is migrated from the source field to the target field only if the predicate passes.

Code Value	Predicate	Meaning
C	n/a	always create new instance
T	n/a	touch datum ; empty merge
N	0	reject any change ; skip merge
Y	sX & tX	accept any change ; bypass merge
B	s1 & tX	insert or update, no delete
H	s1 & t1	update only if exists
U	sX & t1	update or delete only, no insert
I	sX & t0	insert only, no update or delete
D	s0 & tX	delete only, no update or insert
XR	sX & tX	full vector replacement
XM	s ∪ t	set union, vector merge
XD	s - t	set difference, delete given values
XI	s ∩ t	set intersection, delete missing values
XS	t + s	preserve order insert (allows dupes)
XF	s + t	insert from start (allows dupes)

Diff Codes

Applying the merge results in one of these transitions per primitive value in the target object.

Code Value	Meaning	Transitions
Z	noop / ignore	null <-- null or non-null == non-null
N	new / insert	null <-- non-null
E	edit / update	non-null <-- non-null
D	unset / delete	non-null <-- null
AN	array size increase (tbd)	non-null > non-null
AD	array size decrease (tbd)	non-null < non-null

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