From 9d4054c62db3b3d92c24fc6e58d40b3011f74ba4 Mon Sep 17 00:00:00 2001
From: Rasmus Kaj <kaj@kth.se>
Date: Sun, 7 Aug 2016 00:43:17 +0200
Subject: [PATCH] Add support for ordering with NULLS FIRST or NULLS LAST in
 postgres.

---
 CHANGELOG.md                                  |  4 +
 .../src/pg/expression/expression_methods.rs   | 92 +++++++++++++++++++
 diesel/src/pg/expression/predicates.rs        |  3 +
 3 files changed, 99 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 390ebeff51..cf9ef5e51e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,10 @@ for Rust libraries in [RFC #1105](https://github.com/rust-lang/rfcs/blob/master/
 
 ## Unreleased
 
+* Added support for PostgreSQL `NULLS FIRST` and `NULLS LAST` when sorting.
+  See http://docs.diesel.rs/diesel/prelude/trait.SortExpressionMethods.html
+  for details.
+
 ## [0.7.0] - 2016-08-01
 
 ### Added
diff --git a/diesel/src/pg/expression/expression_methods.rs b/diesel/src/pg/expression/expression_methods.rs
index 77baeb3584..eca9018f0e 100644
--- a/diesel/src/pg/expression/expression_methods.rs
+++ b/diesel/src/pg/expression/expression_methods.rs
@@ -211,3 +211,95 @@ impl<T, ST> ArrayExpressionMethods<ST> for T where
     T: Expression<SqlType=Array<ST>>,
 {
 }
+
+use expression::predicates::{Asc, Desc};
+
+pub trait SortExpressionMethods : Sized {
+    /// Specify that nulls should come before other values in this ordering.
+    /// Normally, nulls come last when sorting in ascending order and first
+    /// when sorting in descending order.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # #[macro_use] extern crate diesel;
+    /// # include!("src/doctest_setup.rs");
+    /// #
+    /// # table! {
+    /// #     users {
+    /// #         id -> Integer,
+    /// #         name -> VarChar,
+    /// #     }
+    /// # }
+    /// #
+    /// # table! {
+    /// #     foos {
+    /// #         id -> Integer,
+    /// #         foo -> Nullable<Integer>,
+    /// #     }
+    /// # }
+    /// #
+    /// # fn main() {
+    /// #     let connection = connection_no_data();
+    /// #     connection.execute("DROP TABLE IF EXISTS foos").unwrap();
+    /// connection.execute("CREATE TABLE foos (id SERIAL PRIMARY KEY, foo INTEGER)").unwrap();
+    /// connection.execute("INSERT INTO foos (foo) VALUES (NULL), (1), (2)").unwrap();
+    ///
+    /// #     use self::foos::dsl::*;
+    /// assert_eq!(Ok(vec![Some(1), Some(2), None]),
+    ///            foos.select(foo).order(foo.asc()).load(&connection));
+    /// assert_eq!(Ok(vec![None, Some(1), Some(2)]),
+    ///            foos.select(foo).order(foo.asc().nulls_first()).load(&connection));
+    /// #     connection.execute("DROP TABLE foos").unwrap();
+    /// # }
+    /// ```
+    fn nulls_first(self) -> NullsFirst<Self> {
+        NullsFirst::new(self)
+    }
+
+    /// Specify that nulls should come after other values in this ordering.
+    /// Normally, nulls come last when sorting in ascending order and first
+    /// when sorting in descending order.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # #[macro_use] extern crate diesel;
+    /// # include!("src/doctest_setup.rs");
+    /// #
+    /// # table! {
+    /// #     users {
+    /// #         id -> Integer,
+    /// #         name -> VarChar,
+    /// #     }
+    /// # }
+    /// #
+    /// # table! {
+    /// #     foos {
+    /// #         id -> Integer,
+    /// #         foo -> Nullable<Integer>,
+    /// #     }
+    /// # }
+    /// #
+    /// # fn main() {
+    /// #     let connection = connection_no_data();
+    /// #     connection.execute("DROP TABLE IF EXISTS foos").unwrap();
+    /// connection.execute("CREATE TABLE foos (id SERIAL PRIMARY KEY, foo INTEGER)").unwrap();
+    /// connection.execute("INSERT INTO foos (foo) VALUES (NULL), (1), (2)").unwrap();
+    ///
+    /// #     use self::foos::dsl::*;
+    /// assert_eq!(Ok(vec![None, Some(2), Some(1)]),
+    ///            foos.select(foo).order(foo.desc()).load(&connection));
+    /// assert_eq!(Ok(vec![Some(2), Some(1), None]),
+    ///            foos.select(foo).order(foo.desc().nulls_last()).load(&connection));
+    /// #     connection.execute("DROP TABLE foos").unwrap();
+    /// # }
+    /// ```
+    fn nulls_last(self) -> NullsLast<Self> {
+        NullsLast::new(self)
+    }
+}
+
+impl<T> SortExpressionMethods for Asc<T> {}
+
+impl<T> SortExpressionMethods for Desc<T> {}
diff --git a/diesel/src/pg/expression/predicates.rs b/diesel/src/pg/expression/predicates.rs
index f058e612c4..b9274fff93 100644
--- a/diesel/src/pg/expression/predicates.rs
+++ b/diesel/src/pg/expression/predicates.rs
@@ -1,6 +1,9 @@
 use pg::Pg;
+use query_builder::QueryBuilder;
 
 infix_predicate!(IsNotDistinctFrom, " IS NOT DISTINCT FROM ", backend: Pg);
 infix_predicate!(OverlapsWith, " && ", backend: Pg);
 infix_predicate!(Contains, " @> ", backend: Pg);
 infix_predicate!(IsContainedBy, " <@ ", backend: Pg);
+postfix_expression!(NullsFirst, " NULLS FIRST", ());
+postfix_expression!(NullsLast, " NULLS LAST", ());