Re: [apps-discuss] draft-snell-merge-patch-08 in Ruby

["Manger, James H" <[e-mail]>]

> Given James M's example cases, the results should be:
> 
> > Document + patch = ?
> 
> > [1,2]  +  {"a":"foo","b":null}
> 
>   Result: {"a":"foo"}

The JavaScript in draft-snell-merge-patch-08 incorrectly gives the result as [1,2].


> > {"a":"foo"}  +  {"b":[3,null,{"x":null}]}
> 
>   Result: {"a":"foo", "b":[3,{}]}

NO. The result should be: {"a":"foo", "b":[3,null,{"x":null}]}.
Merge-patch does NOT merge arrays; it treats them like other primitives (strings, numbers, booleans) so a merge-patch implementation should NOT be looking inside an array for nulls.

The JavaScript in draft-snell-merge-patch-08 gives neither of these results. It incorrectly gives {"a":"foo", "b":[3,{"x":null}]}


> > {"a":"foo"}  +  null
> 
>   Result: Invalid. The patch document MUST be a valid JSON document,
> which means the root must be either a JSON object or array. A null
> patch document is invalid.

I thought the one non-controversial change planned for RFC4627 "JSON" was to allow any JSON value (not just arrays and objects) as a JSON-text.

A patch of null certainly should not return the original unchanged (as the JavaScript in draft-snell-merge-patch-08 does). Either throw an error, or return an undefined value.


> If there is an error in the javascript impl in the draft, I'll make
> sure that gets corrected in the next iteration.

My suggested JavaScript implementation:

function merge(orig, patch) {
	var result;
	if (patch === null) {
		// leave result undefined
	}
	else if (typeof patch === 'string' ||
		typeof patch === 'number' ||
		typeof patch === 'boolean' ||
		Array.isArray(patch))
	{
		result = patch;
	}
	else { // patch is an object
		result = {};
		if (orig instanceof Object && !Array.isArray(orig)) {
			for (m in orig)
				result[m] = orig[m];
		}
		for (m in patch) {
			result[m] = merge(result[m], patch[m]);
		}
	}
	return result;
}

See it in action at http://id.cto.telstra.com/json/merge.html

--
James Manger