add official API to have naming conventions work for alternate constraint types

[CaselIT]

Using them is poorly tested and the use case seems quite limited.

[zzzeek]

as stated, how do we supply naming conventions for ExcludeConstraint as well as any other third party constraint? that was likely why I had it supporting this style

[CaselIT]

are they supported at the moment?

This #3011 seems also related

[zzzeek]

i dont know, not sure if we have tests. we'd want to see if there are excludeconstraint naming convention tests in PG (I dont think there are)

[CaselIT]

I guess the objective of the issue is then:

• verify if other contraints work when passed aw type
• if they do properly test the feature/improve typing as needed
• if not then we could probably consider deprecating this

[zzzeek]

if we deprecate then we need a new way to support naming conventions for other constraint types

[CaselIT]

well the thinking was if it does not work at the moment then chances are no-one wants-uses it

[zzzeek]

constraint types that are not in the immediate schema.py hierarchy are pretty major. some way to register a new two letter code, something like that. just cant be a brick wall

[zzzeek]

I guess the idea here was the naming convention dict allows arbitrary keys and can't use TypedDict? I definitely think custom letter codes should be allowed in that dict, in any case. A full expansion of naming convention stuff to other constraints would be nice also but not priority.

unless we want to move this to "make an official extensibility API for naming conventions" I would say we close this

[puc9]

I actually use the naming conventions a lot and, not realizing it is not supported, I have custom ones added.
To add a custom constraint naming convention:

# Define the custom naming convention
CONSTRAINTS_NAMING_CONVENTION: _NamingSchemaParameter = {
    'ix': 'IX_%(column_0_label)s',
    'uq': 'UQ_%(table_name)s_%(column_0_N_name)s',
    'ck': 'CK_%(table_name)s_%(constraint_name)s',
    'fk': 'FK_%(table_name)s_to_%(referred_table_name)s',
    'pk': 'PK_%(table_name)s',
    'ctcn_cols': ctcn_columns,
    'ctcn': 'UQ_%(table_name)s[%(ctcn_cols)s]_per_%(referred_table_name)s',
}

# Define the custom constraint
class CustomConstraint(UniqueConstraint): ...

# Add the prefix and the type:
_prefix_dict[CustomConstraint] = 'ctcn'

# Define the callback function
def ctcn_columns(constraint: Constraint, table: Table) -> str:
    if not isinstance(constraint, CustomConstraint):
        return ''

    str_tokens = # add your logic here
    return '_'.join(str_tokens)

I think this was working fine in alembic as well, but I don't have any code handy to double check.

I don't know what would need to be added to make this supported, but I don't think that it should be that much since it is working just fine using the private variable _prefix_dict.

Other than that, I think that the _NamingSchemaParameter should be public since you would need it to properly document the dictionary that defines the custom rules.