Expose validate()

[wolfgangwalther]

Currently, only is_valid() is exposed, which just returns a bool.

It would be great to expose validate(), too, to get actual validation errors thrown (with information about why the validation is failing...).

[duguorong009]

@wolfgangwalther @olirice
I would like to contribute to the project, and take this issue.
Can you take a look at PR #32 ?

[zakandrewking]

I wonder if this would make it possible to return meaningful validation errors for CHECK constraints. For now, all we get for an invalid insert is:

ERROR:  new row for relation "node" violates check constraint "node_column_check"
DETAIL:  Failing row contains (... some data ...).

[olirice]

resolved by #32