Hi Daniel
2016-05-12 20:20 GMT+02:00 <[email protected]>:
> I think I found a problem in the jooq Field type hierarchy.
>
> Lets say I start with a few TableFields. My SQL generation does some
> field filtering based off of fields' tables, so later code needs to be able
> to call .getTable() on them.
>
> Now, lets say I'm joining across two tables and have two columns called
> ID. In certain queries, this will create a "Duplicate column name 'id'"
> error (eg if these are part of an inner subselect that gets selected out).
>
> So, I need to alias one of my TableFields, for example MY_TABLE.ID.as
> ("joinedId").
>
> However, because .as() is part of the Field interface and returns a Field,
> my code that depends on a list of TableFields to do the .getTable() breaks
> apart at the type level. I can't typecast back up to TableField because
> .as() actually returns a different implementation under the hood.
>
That's correct.
> Is there any reason why the TableField interface can't override the
> inherited .as() function and declare it as returning a TableField instead
> of a Field?
>
Yes, because the returned field (expression) is no longer a TableField.
When you declare an aliased field (in the SELECT clause), it does render
the underlying table on the left hand side of the AS keyword, but the
expression itself (e.g. as rendered in the ORDER BY clause) really does not
have any notion of being part of a table. Specifically, there's a use-case
when you use an alias to dereference a column from a nested select /
derived table:
Field<?> joinedId = MY_TABLE.ID.as("joinedId");
Table<?> derivedTable =
table(select(joinedId).from(...)).as("derivedTable");
Field<?> derivedTableJoinedId = derivedTable.field(joinedId); // This is
now "derivedTable"."joinedId"
As you can see, while there was, at some point, the notion of an ID column
that belongs to a MY_TABLE table, that notion cannot be maintained
throughout such expression transformations. In the end, the only thing that
is really guaranteed is the fact that your field's name is "joinedId".
May have to play with the underlying Impl's to get it right, but in theory,
> calling TableField.as() /should/ return a TableField, just with an added
> alias.
>
No, because it would be wrong to fully qualify the alias with the original
table name. The original table name no longer exists. The only thing that
exists now is the alias.
Note, this is different from aliasing a table, which produces a new table
with columns that reference the aliased table.
Alternatively, is there a different way I can alias one of my TableFields
> while still being able to later call .getTable() on it?
>
There are many ways to solve similar problems. I think it would help to
first better understand your use-case, e.g. why you want to disambiguate
(in a generic fashion) the duplicate ID columns. For instance, SQL doesn't
have any problems with duplicate column names in top level selects. Neither
does jOOQ. So, what's the use-case you're trying to solve here?
2016-05-12 20:20 GMT+02:00 <[email protected]>:
> I think I found a problem in the jooq Field type hierarchy.
>
> Lets say I start with a few TableFields. My SQL generation does some
> field filtering based off of fields' tables, so later code needs to be able
> to call .getTable() on them.
>
> Now, lets say I'm joining across two tables and have two columns called
> ID. In certain queries, this will create a "Duplicate column name 'id'"
> error (eg if these are part of an inner subselect that gets selected out).
>
> So, I need to alias one of my TableFields, for example MY_TABLE.ID.as
> ("joinedId").
>
> However, because .as() is part of the Field interface and returns a Field,
> my code that depends on a list of TableFields to do the .getTable() breaks
> apart at the type level. I can't typecast back up to TableField because
> .as() actually returns a different implementation under the hood.
>
> -----
>
> Is there any reason why the TableField interface can't override the
> inherited .as() function and declare it as returning a TableField instead
> of a Field? May have to play with the underlying Impl's to get it right,
> but in theory, calling TableField.as() /should/ return a TableField, just
> with an added alias.
>
> Alternatively, is there a different way I can alias one of my TableFields
> while still being able to later call .getTable() on it?
>
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