Thread

1. Re: Question about inheritance

   Dmitry G. Mastrukov Дмитрий Геннадьевич Мастрюков <dmitry@taurussoft.org> — 2001-06-05T10:17:33Z

    > "Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
    > > Am I misunderstanding how the mechanism works, or is this a big, not
    easily
    > > solved, problem?
    >
    > The latter.  Check the list archives for previous debates about this.
    > It's not real clear whether an inherited primary key should be expected
    > to be unique across the whole inheritance tree, or only unique per-table
    > (IIRC, plausible examples have been advanced for each case).  If we want
    > uniqueness across multiple tables, it'll take considerable work to
    > create an index mechanism that'd enforce it.
    >
    IMHO current behaviour of PostgreSQL with inherited PK, FK, UNIQUE is
   simply
    bug not only from object-oriented but even object-related point of view.
   Now
    I can violate parent PK by inserting duplicate key in child!
   
    Inherited tables should honours all constraints from parent. If I change
    some constraint (seems only FK, but not PK or UNIQUE) I should be able to
   do
    it in more restrictive manner. For example, two base table is connected via
    FK. I can change such FK in childs from base1->base2 to child1->child2 (or
    child3) but not to child1->not_inherited_from_base2. CHECK, DEFAULT, NOT
    NULL are more free to changes, isn't it?
   
    IMHO last message in doc/TODO.details/inheritance from Oliver Elphick is a
    good direction for implementing with exception on more rectrictive child FK
    constraint (p.3 of message).
   
    As for me, I was pushed to rollback to scheme with no inheritance at all in
    my project for now. So I'm very interesting in implementing of right
    inheritance and I wanted to ask similar question in one of the lists in
   near
    future.
   
    Regards,
    Dmitry
   
   
   
   
   

2. Re: Question about inheritance

   Bruce Momjian <pgman@candle.pha.pa.us> — 2001-06-10T03:48:30Z

   I have added this thread to TODO.detail/inheritance.
   
   >  > "Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
   >  > > Am I misunderstanding how the mechanism works, or is this a big, not
   >  easily
   >  > > solved, problem?
   >  >
   >  > The latter.  Check the list archives for previous debates about this.
   >  > It's not real clear whether an inherited primary key should be expected
   >  > to be unique across the whole inheritance tree, or only unique per-table
   >  > (IIRC, plausible examples have been advanced for each case).  If we want
   >  > uniqueness across multiple tables, it'll take considerable work to
   >  > create an index mechanism that'd enforce it.
   >  >
   >  IMHO current behaviour of PostgreSQL with inherited PK, FK, UNIQUE is
   > simply
   >  bug not only from object-oriented but even object-related point of view.
   > Now
   >  I can violate parent PK by inserting duplicate key in child!
   > 
   >  Inherited tables should honours all constraints from parent. If I change
   >  some constraint (seems only FK, but not PK or UNIQUE) I should be able to
   > do
   >  it in more restrictive manner. For example, two base table is connected via
   >  FK. I can change such FK in childs from base1->base2 to child1->child2 (or
   >  child3) but not to child1->not_inherited_from_base2. CHECK, DEFAULT, NOT
   >  NULL are more free to changes, isn't it?
   > 
   >  IMHO last message in doc/TODO.details/inheritance from Oliver Elphick is a
   >  good direction for implementing with exception on more rectrictive child FK
   >  constraint (p.3 of message).
   > 
   >  As for me, I was pushed to rollback to scheme with no inheritance at all in
   >  my project for now. So I'm very interesting in implementing of right
   >  inheritance and I wanted to ask similar question in one of the lists in
   > near
   >  future.
   > 
   >  Regards,
   >  Dmitry
   > 
   > 
   > 
   > 
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