12:23 p.m.
On 27 May 2015, at 5:49, Steve Ebersole wrote:
If anyone is interested, the issue is here:
https://hibernate.atlassian.net/browse/HHH-9820
I do wonder overall about the interplay that should happen between a
Dialect and the JdbcEnvironment.
I reckon your issue is that you need access to Dialect before you might
have a DatabaseMetaData so you can't give that to the Dialect to hold on
to ?
Thus having some parameter to Dialect that allows access to
DatabaseMetaData
would be most sensible I would think.
One concern about DatabaseMetaData that hit the tools a few times is
that
getting this can be extremely expensive for some drivers (I don't recall
which
exactly, but Oracle comes to mind ;)
Thus if you do add it as a parameter to Dialect calls, it might be worth
proxying or wrap DatabaseMetaData. Also be aware that DatabaseMetaData
might
actually *require* a connection to a database which is not optimal
for tools that might want to just get a script generated without
requiring
full access to a database.
/max
On Tue, May 26, 2015 at 10:29 PM, Steve Ebersole <steve(a)hibernate.org>
wrote:
> What follows is solely an issue with schema update and schema
> validation,
> 2 tools that to date we have not "really" supported, but I am trying
> to
> change that with 5.0.
>
> We discussed before the idea of auto-quoting and who should be the
> authority in regards to keywords. We decided that it would be
> Dialect, for
> Dialects that chose to do it, rather than the JDBC DatabaseMetaData.
> However there is another piece to this that we currently miss. It
> has to
> do with the following methods:
>
> * java.sql.DatabaseMetaData#storesMixedCaseQuotedIdentifiers
> * java.sql.DatabaseMetaData#storesLowerCaseQuotedIdentifiers
> * java.sql.DatabaseMetaData#storesUpperCaseQuotedIdentifiers
> * java.sql.DatabaseMetaData#storesMixedCaseIdentifiers
> * java.sql.DatabaseMetaData#storesUpperCaseIdentifiers
> * java.sql.DatabaseMetaData#storesLowerCaseIdentifiers
>
> We already have bug reports that come directly from drivers not
> implementing these "properly".
>
> They come into play in the implementation of the following methods
> (on
> org.hibernate.engine.jdbc.env.spi.IdentifierHelper):
>
> * toMetaDataCatalogName
> * toMetaDataSchemaName
> * toMetaDataObjectName
> * fromMetaDataCatalogName
> * fromMetaDataSchemaName
> * fromMetaDataObjectName
>
> The to* methods are used when binding the Identifiers to the metadata
> queries (DatabaseMetaData#getTables method e.g.). The from* methods
> are
> used when extracting values from the results. We currently rely on
> the
> answers to the referenced DatabaseMetaData methods to determine the
> quoting->case conversion and case->quoting conversions.
>
> My proposal is that we go a step further than what we did for Dialect
> and
> auto-quoting. For that, we defined a
> Dialect#determineKeywordsForAutoQuoting method and allowed Dialects
> to
> override it if they wanted. The only time that method is used
> actually is
> in building the IdentifierHelper instance. So my proposal is that we
> drop
> Dialect#determineKeywordsForAutoQuoting and instead define a
> Dialect#buildIdentifierHelper method. This could work one of 2 ways.
>
> First, the Dialect#buildIdentifierHelper method accepts a
> DatabaseMetaData
> and the base implementation would do what we do today. However,
> DatabaseMetaData can very well be null. When we initialize
> IdentifierHelper atm we assume some (H2 based) defaults. So going
> this
> first route would mean each Dialect impl that wants to override this
> method
> having to handle nulls there. Not ideal.
>
> A second approach would be to have Dialect#buildIdentifierHelper
> accept
> either no parameters or just one parameter which would be the same as
> what
> is passed to Dialect#determineKeywordsForAutoQuoting. This would
> work such
> that null returned from this method would mean to use a fallback
> approach
> based on DatabaseMetaData.
>
> What do y'all think?
>
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/max
http://about.me/maxandersen