Add a method to remove resources from graph

[claudiu-cristea]

Fixes #43

[k00ni]

@claudiu-cristea thank you, its a helpful addition. Would you mind adding a unit test that covers the new code?

[claudiu-cristea]

I will add but very busy ATM

[k00ni]

I didn't check it thoroughly, but do you cover the following cases?

1. Resource A is subject
2. Resource A is predicate
3. Resource A is object

If I understand #43 correctly, all existing instances of a given resource are to be removed. Correct?

[claudiu-cristea]

If you have these triples:

<http://example.com/subject/1> <http://example.com/predicate/1> "value 1.1.1"
<http://example.com/subject/1> <http://example.com/predicate/1> "value 1.1.2"
<http://example.com/subject/1> <http://example.com/predicate/2> "value 1.2.1"
<http://example.com/subject/1> <http://example.com/predicate/3> "value 1.3.1"
<http://example.com/subject/2> <http://example.com/predicate/1> "value 2.1.1"
<http://example.com/subject/2> <http://example.com/predicate/2> "value 2.2.1"

and I run `$graph->deleteEntireResource('http://example.com/subject/1');

the graph will contain only:

<http://example.com/subject/2> <http://example.com/predicate/1> "value 2.1.1"
<http://example.com/subject/2> <http://example.com/predicate/2> "value 2.2.1"

I'm not sure I understand your case

[k00ni]

I'm not sure I understand your case

Lets suppose you have:

<http://foo/1> <http://bar/1> <http://baz/1> .
<http://example/2> <http://foo/1> <http://example/3> .
<http://example/a> <http://example/b> <http://foo/1> .

After calling deleteEntireResource('http://foo/1'); all these triples are gone, because http://foo/1 is part of them. Is that how you want deleteEntireResource to work?

[k00ni]

@claudiu-cristea I refined your function based on my last comment. Does it act the way you described it?

[claudiu-cristea]

Initially I didn't think about the triples referring the deleted resources. I really don't know whether we need to delete also those triples. I'm thinking that they can be referred from other graphs (???). No strong opinion. However, if we follow those related resources, I think we need to make this optional (i.e., with an option). Let's not rush, I need to reflect more on this

[zozlak]

I guess what you want is to only delete all triples having a given subject.

In such a case I would suggest to make it the easyrdf\Resource::deleteAll() method or adjust the already existing easyrdf\Resource::delete() in a way it can be called with no parameters (which would be interpreted as "delete all").

The tricky part about it is the state of the easyrdf\Resource object after the removal of all triples having it as a subject. If a given easyrdf\Resource was only used as a subject, it will be left in an "existing but not-used" state. From the pragmatic perspective I don't think it's an issue though. The user doesn't care as (s)he got what (s)he wanted and we already can create easyrdf\Resource in such a state:

$graph = new easyrdf\Graph();
$resource = $graph->resource('https://foo');

so it would not any new corner case to the library.

The problem with the easyrdf\Graph::deleteWholeResource() is as outlined by @k00ni - in the easyrdf data model a resource represents both triples' subjects, predicates (properties) and objects so the easyrdf\Graph::deleteWholeResource() sounds quite ambiguous.

[claudiu-cristea]

@zozlak

I guess what you want is to only delete all triples having a given subject.

Yes, this is exactly what I need.

In such a case I would suggest to make it the easyrdf\Resource::deleteAll() method...

Sounds better. I will provide shortly some commits on this direction

[k00ni]

Closed for now to avoid stale PRs. Also, @zozlak made some good points.

Please get back to me if you wanna continue here.