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Add ability to select without a from clause #97

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sgrif opened this Issue Jan 15, 2016 · 0 comments

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sgrif commented Jan 15, 2016

I'm trying to more thoroughly test some cases, and I've got a lot of code that looks like:

connection.query_sql_params::<Bool, bool, Timestamp, SystemTime>(
    "SELECT $1::timestamp = '1970-01-01'", &UNIX_EPOCH)
.unwrap().nth(0).unwrap()

I'd like to instead be able to write

select(sql("'1970-01-01'").eq(UNIX_EPOCH))
    .first(&connection).unwrap()

This will require some changes to SelectStatement which make the from clause optional. I'm unsure if I want to allow select(foo).from(bar)

@sgrif sgrif added the enhancement label Jan 15, 2016

@sgrif sgrif referenced this issue Jan 16, 2016

Merged

Implement FromSql and ToSql for `chrono::NaiveTime` #101

@sgrif sgrif closed this in c26d299 Jan 16, 2016

mcasper added a commit to mcasper/diesel that referenced this issue Jan 17, 2016

@sgrif @mcasper
Add a bare `select` function for select statements with no from clause 
In addition to this function, I have also added a `sql` function, which
is shorthand for `SqlLiteral` (but only takes `&str`, not `String`), and
`in_time_zone` which is not part of the public API.

`sql` takes `&str`, instead of `T: Into<String>`, because the first type
parameter is always going to need to be passed, and I find
`sql::<Timestamp, _>` ugly. There's always `SqlLiteral::new` if you need
to pass a `String`, or you can just deref it to `str` and accept the
copying.

I had hoped to eliminate `query_sql_params`, but there's one test we
have that's using it which requires a where clause. I can't just hack it
and do `select(sql("1 WHERE ..."))` because it uses bind params. I'll
implement `FilterDsl` for `BareSelectStatement` at some point. I'd also
like to remove `query_sql`, as I think that `select(sql` covers it
suffciently.

I've opted to leave `in_time_zone` out of the public API, as it should
actually have the return type of `Timestamptz`, and I'm really unsure
how various infix predicates with the lhs being `Timestamp` and the rhs
being `Timestamptz` are going to interact. We might be able to get away
with just not allowing it and have it be a non-issue, similarly to
`VarChar` and `Text`, but it needs further exploration.

Fixes diesel-rs#97.
b0946bf
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