Comments (8)
Great, in that case maybe we can do them all as versions of a single "write type" that is something like
WriteField a = Omitted | SetToDefault | SetToValue a
from haskell-opaleye.
Just to check I understand, do the writing parts of these behave as indicated in the following?
-- Generates "field = value"
requiredTableField :: String -> TableFields (Field_ n a) (Field_ n a)
writeOnlyRequiredTableField :: String -> TableFields (Field_ n a) ()
-- Just: Generates "field = value"
-- Nothing: Generates "field = DEFAULT"
optionalTableField :: String -> TableFields (Maybe (Field_ n a)) (Field_ n a)
writeOnlyOptionalTableField :: String -> TableFields (Maybe (Field_ n a)) ()
-- Generates nothing for "field"
readOnlyTableField :: String -> TableFields () (Field_ n a)
missingTableField :: TableFields () ()
from haskell-opaleye.
Correct!
from haskell-opaleye.
I just noticed a related issue on rel8: circuithub/rel8#193
from haskell-opaleye.
Yeah I think many Haskell db libraries handle this type of stuff poorly. I don't think persistent
handles default/generated columns well either.
from haskell-opaleye.
As a side note
readOnlyTableField
does actually work correctly for generated columns due to them allowing the keywordDEFAULT
for inserts and updates even though all other values are rejected due to their read-only nature.
For updates, Opaleye generates a syntactically valid query that will actually "typecheck" against the schema, so to speak, but unless the DEFAULT
value is a constant, the semantics of that query is likely not what you want:
db=# create temp table t(
id integer primary key generated always as identity,
created_at timestamptz not null default now(),
v integer not null
);
CREATE TABLE
db=# insert into t(v) values(1);
INSERT 0 1
db=# select * from t;
id | created_at | v
----+-------------------------------+---
1 | 2024-05-20 08:13:51.872027+00 | 1
db=# update t set v = 2;
UPDATE 1
db=# select * from t;
id | created_at | v
----+-------------------------------+---
1 | 2024-05-20 08:13:51.872027+00 | 2
db=# update t set v = 3, id = default, created_at = default;
UPDATE 1
db=# select * from t;
id | created_at | v
----+-------------------------------+---
2 | 2024-05-20 08:14:21.103436+00 | 3
The query updates the field by recomputing the DEFAULT
expression. In particular, this means that a table with a DEFAULT
ed foreign key target cannot be updated in this manner (since that would violate referential integrity).
(Which is just to say that the "nothing generated, not even DEFAULT
" case is vital.)
from haskell-opaleye.
Ah, I see this was mentioned in #590 (comment) and you were talking about generated columns, not theβ¦serial
thing.
from haskell-opaleye.
Yes just GENERATED ALWAYS AS ( generation_expr ) STORED
from haskell-opaleye.
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