Allow now to be used as a Nullable<Timestamptz>

Fixes diesel-rs#1031

Author: Eijebong

diesel/src/expression/functions/date_and_time.rs

@@ -69,3 +69,12 @@ impl AsExpression<Timestamptz> for now {
         Coerce::new(self)
     }
 }
+
+#[cfg(feature="postgres")]
+impl AsExpression<Nullable<Timestamptz>> for now {
+    type Expression = Coerce<now, Nullable<Timestamptz>>;
+
+    fn as_expression(self) -> Self::Expression {
+        Coerce::new(self)
+    }
+}

diesel_tests/tests/expressions/date_and_time.rs

@@ -2,6 +2,7 @@ use schema::{connection, TestConnection};
 use diesel::*;
 use diesel::data_types::*;
 use diesel::expression::dsl::*;
+use diesel::types::Nullable;
 
 table! {
     has_timestamps {
@@ -59,6 +60,25 @@ fn now_can_be_used_as_timestamptz() {
     assert_eq!(Ok(vec![1]), before_now);
 }
 
+#[test]
+#[cfg(feature = "postgres")]
+// FIXME: Replace this with an actual timestamptz expression
+fn now_can_be_used_as_nullable_timestamptz() {
+    use self::has_timestamps::dsl::*;
+    use diesel::types::Timestamptz;
+
+    let connection = connection();
+    setup_test_table(&connection);
+    connection.execute("INSERT INTO has_timestamps (created_at) VALUES \
+                        (NOW() - '1 day'::interval)").unwrap();
+
+    let created_at_tz = sql::<Nullable<Timestamptz>>("created_at");
+    let before_now = has_timestamps.select(id)
+        .filter(created_at_tz.lt(now))
+        .load::<i32>(&connection);
+    assert_eq!(Ok(vec![1]), before_now);
+}
+
 #[test]
 #[cfg(feature = "sqlite")]
 fn now_executes_sql_function_now() {