[hibernate-dev] Naming and "naming strategies"

[Gunnar Morling]

> Do we need a contract for LogicalNamingStrategy?

As you say it's an internal concept only. Based on your description I don't
see why a user would want to customize it. So I'd internally make
consistently use of the LogicalNamingStrategy for resolving references, but
I'd not make it pluggable. Should someone really need this, it's easy to
make it pluggable later on.

> So I also propose to shift this to use that Identifier class

I like that idea.

Is it correct to say it represents a logical name basically? If so, how
about naming it "LogicalName"? "Identifier" seems too generic to me (e.g.
easily to be mixed up with entity identifiers). Would that class/interface
define a method String getPhysicalName()? That should nicely encapsulate
the quote handling.

> But is poses a problem when the same table name is used from different
schemas. [... ] The only other option I can see is to define a limitation
that says that a table name must
be unique for a given entity across all catalogs/schemas. [...] that is
generally a restrictive limitation.  What are y'alls thoughts? Perhaps this
is one argument for allowing pluggable LogicalNamingStrategy?

I'd work with that restriction. I would not make LogicalNamingStrategy
pluggable just for this, until someone comes up with really compelling use
case why they'd need that sort of mapping.

--Gunnar


2015-01-13 19:43 GMT+01:00 Steve Ebersole <steve at hibernate.org>:

> As I am working on 5.0, one of the things I am trying to accomplish is to
> make the handling of table/column names more consistent and better
> defined.  The first step in that is to properly define the terms used often
> throughout the codebase.
>
> The first level of naming is the "given" name of a table/column.  The given
> name might be:
> * explicit - explicitly specified by the user, as in @Table(
> name="explicit_name" )
> * implicit - not explicitly specified by the user and thus implicitly
> determined (by JPA rules, "naming strategy", etc).
>
> Next, we have a logical name which is a normalized form of the "given"
> name.  This is the form used to reference tables/columns internally.  E.g.,
> its how we resolve @Column(..., table="xyz").  More on this form later.
>
> Finally we have the physical name of the thing, which is the actual name of
> the table/column in the database.  Again, this is generally a normalization
> of the given name based on Dialect, "naming strategy", etc.
>
> Today, we have a very messy concept called a NamingStrategy.  I say it is
> messy because it tries to combine unrelated concerns.  So I still plan to
> split this as I have outlined elsewhere into:
> 1) ImplicitNamingStrategy
> 2) PhysicalNamingStrategy
>
> Which brings up my first question to y'all.  Do we need a contract for
> LogicalNamingStrategy?  As I have said, the logical names are the things
> used to resolve references.  Allowing people to plug in custom strategies
> for how that normalization works could be very dangerous.  But even more
> than that, is it really interesting to be able to hook into that process?
>
> Historically, these names are all represented by String.  So I also propose
> to shift this to use that Identifier class we developed for the metamodel
> redesign.  For those that may be unfamiliar, it essentially combines the
> String name with a "quoted" boolean:
>
> public class Identifier {
>   private final String text;
>   private final boolean isQuoted;
>     ...
> }
>
> Table names, then, are an aggregation of 3 Identifiers: one for catalog,
> one for schema, one for table name.  Same for named constraints
> (ultimately, which is part of a improvement for 6.0 to allow indexes,
> constraints, etc to be created in a separate schema from tables).
>
> Since a major goal for 5.0 is to continue to use the org.hibernate.mapping
> package as the representation of the mapping information, we obviously want
> to minimize changes there to only what is completely essential.  To that
> end, if we are going to use Identifier over String stuff in the
> org.hibernate.mapping package will need to deal with both; internally they
> will hold the Identifier and use that to implement the String-based
> name-related methods they expose.
>
> Lastly I wanted to discuss the details of the logical names.  For tables,
> we currently qualify the table name with the catalog/schema info.  There is
> a mismatch in this regard when it comes to remaining a pure JPA
> implementation.  Consider @Column( ..., table="some_table").  Ultimately we
> need to be able to qualify that with catalog/schema in order to be able to
> construct a matching logical name (to be able to pair that with the
> referenced org.hibernate.mapping.Table later).  This is trivial when table
> names are unique across all the catalogs/schemas (when there is only one
> "some_table" in all the mapped catalogs/schemas).  But is poses a problem
> when the same table name is used from different schemas (e.g., when
> "some_table" is mapped from both "schema1" and "schema2").  So we have a
> choice.  Since JPA does not say what is legal/illegal for the @Column.table
> attribute, it is feasible for us to allow @Column.table to contain the
> catalog/schema information in these cases as a selector.  The only other
> option I can see is to define a limitation that says that a table name must
> be unique for a given entity across all catalogs/schemas.  I don't think
> that is generally a restrictive limitation.  What are y'alls thoughts?
> Perhaps this is one argument for allowing pluggable LogicalNamingStrategy?
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