update queries: allow to copy fields

[dbu]

It would be awesome if this query would work:

UPDATE [nt:unstructured] AS a INNER JOIN [nt:unstructured] AS t ON ISCHILDNODE(t, a) SET t.linkCaption = a.linkCaption WHERE a.[phpcr:class] = 'Liipch\MagazineBundle\Document\Article' ;

but the update processor would need to evaluate the value side, we get

[PHPCR\ValueFormatException] Invalid value for property "originalLinkCaption": Object values must implement PHPCR\NodeInterface, PHPCR\PropertyInterface or be \DateTime, supplied argument is of class: PHPCR\Shell\Query\ColumnOperand

[dantleech]

Might be easy, depends on the parser. I started writing a new parser implementation but it seems it was one of the few things I pushed to github before I lost the contents of my harddrive :(

[dantleech]

This should be possible with the EXPR function btw.