Select from a sql function

[fluxxu]

Now diesel has a sql_function! macro which allows we map a SQL function to query DSL, but I can't figure out a way to map a function to return a table.

For example, it seems that there is no way to select from this function:

CREATE TABLE tbl_function_return_data (
  id serial,
  text_value text,
  int_value integer,
  PRIMARY KEY(id)
);

CREATE FUNCTION function_return_table(v1 integer, v2 text)
  RETURNS TABLE(
    id integer,
    text_value text,
    int_value integer
  )
AS
$$
  SELECT * FROM tbl_function_return_data WHERE int_value > v1 OR text_value = v2
$$
LANGUAGE 'sql' IMMUTABLE;

To make diesel compiles, we can

sql_function!(function_return_table, function_return_table_t, (v1: Integer, v2: VarChar) -> (i32, String, i32));

diesel::select(tbl_function_return_data(1, "string")).load::<(i32, String, i32)>(conn);

But this generates a query as

SELECT tbl_function_return_data(1, 'string');

which returns a tuple instead of a record set, which causes a DeserializationError.
The query we actually need is:

SELECT * FROM tbl_function_return_data(1, 'string');

To generate this query, I tried

diesel::expression::SelectStatement::simple(tbl_function_return_data(1, "string")).load::<(i32, String, i32)>(conn);

To make this compiles, I need to impl QuerySource for function_return_table_t:

impl<A: Clone, B: Clone> QuerySource for function_return_table_t<A, B> {
  type FromClause = Self;
  type DefaultSelection = SqlLiteral<(Integer, VarChar, Integer)>;

  fn from_clause(&self) -> Self::FromClause {
    self.clone()
  }

  fn default_selection(&self) -> Self::DefaultSelection {
    SqlLiteral::new("*".to_owned())
  }
}

My question is should we have a macro like

sql_function_query_souce!(
  function_return_table, function_return_table_t, (v1: Integer, v2: VarChar) -> (i32, String, i32)
);

which impl QuerySource?
sql_function + impl QuerySource works, but the return type of sql_function is useless for this use case.

Thanks!

[sgrif]

I think for now sql_query is the best bet for something like this. Support for this is roughly the same as supporting selecting from a subselect, which will come at some point in the future.