Add support for previews

[vilpersson]

Returns languages and translations when querying post previews.

[esamattis]

Merged master here and added tests.

For some reason the testCanHaveLanguageField passed even without your changes.

wp-graphql-polylang/tests/wpunit/PostPreviewQueryTest.php

Lines 25 to 59 in bebf17a

	public function testCanHaveLanguageField()
	{
	$post_id = $this->factory()->post->create([
	'post_title' => 'Original post',
	'post_content' => '',
	'post_type' => 'post',
	'post_status' => 'publish',
	]);
	pll_set_post_language($post_id, 'fi');
	$preview_id = $this->factory()->post->create([
	'post_title' => 'Preview post',
	'post_content' => 'Preview Content',
	'post_type' => 'revision',
	'post_status' => 'inherit',
	'post_parent' => $post_id,
	]);
	pll_set_post_language($preview_id, 'en');
	$query = "
	query Preview {
	post(id: \"$post_id\", idType: DATABASE_ID, asPreview: true) {
	title
	language {
	code
	}
	}
	}
	";
	wp_set_current_user(1);
	$result = do_graphql_request($query);
	$this->assertArrayNotHasKey('errors', $result, print_r($result, true));
	$this->assertEquals($result['data']['post']['language']['code'], 'EN');
	}

Can you eleborate when it failed before?

[esamattis]

Oh wait. Now it fails in the CI 🤔

[vilpersson]

Are you sure that Polylang is setting the language of the preview post?

After creating preview, the newly created revision does not seem get the term relationship to the language taxomony, and this query will return null

query PREVIEW_QUERY {
    page(id: 7844, idType: DATABASE_ID, asPreview: true) {
        title
        language {
            code
        }
    }
}

If you go and check the post id of the revision, and set the language via pll_set_post_language function, then the you'll get correct language.

[esamattis]

It is explicitly set here in the test:

https://github.com/valu-digital/wp-graphql-polylang/pull/30/files#diff-c9b04d9613c130bcf51b35ed35bf1490R42

But I'll test this in a real WP env. Unit testing Polylang correctly is actually quite hard since it's initialization so tied to the normal WP boot up.

[esamattis]

Ah. It seems that in a real WP instance the language of the preview is not set at all so we need to fallback to the language of the original post.

[esamattis]

Merged, thank you!

Made couple additional fixes to this:

Must remove the original parent from the translations list to avoid duplicate entries
659d101

Also needed to use the parent id for the name and locale fields too
c521f30

[esamattis]

Released in v0.5.0
https://github.com/valu-digital/wp-graphql-polylang/releases/tag/v0.5.0

[vilpersson]

@esamattis Great, thank you!