Add a Slice adapter type

Until impl specialization exists, we can't define this implementaion
directly on &[T] because of the existing implementation for &[u8].

Closes rust-postgres#92

Author: sfackler

src/lib.rs

@@ -82,6 +82,8 @@ use url::Url;
 pub use error::{Error, ConnectError, SqlState, DbError, ErrorPosition};
 #[doc(inline)]
 pub use types::{Oid, Type, ToSql, FromSql};
+#[doc(inline)]
+pub use types::Slice;
 use io::{InternalStream, Timeout};
 use message::BackendMessage::*;
 use message::FrontendMessage::*;

src/types/mod.rs

@@ -1,4 +1,6 @@
 //! Traits dealing with Postgres data types
+pub use self::slice::Slice;
+
 use serialize::json;
 use std::collections::HashMap;
 use std::old_io::net::ip::IpAddr;
@@ -132,6 +134,7 @@ macro_rules! to_raw_to_impl {
 #[cfg(feature = "uuid")]
 mod uuid;
 mod time;
+mod slice;
 
 /// A Postgres OID
 pub type Oid = u32;

src/types/slice.rs

@@ -0,0 +1,56 @@
+use byteorder::{BigEndian, WriterBytesExt};
+
+use {Type, ToSql, Result, Error};
+
+/// An adapter type mapping slices to Postgres arrays.
+///
+/// `Slice`'s `ToSql` implementation maps the slice to a one-dimensional
+/// Postgres array of the relevant type. This is particularly useful with the
+/// `ANY` operator to match a column against multiple values without having
+/// to dynamically construct the query string.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// # fn foo() -> postgres::Result<()> {
+/// # use postgres::{Connection, SslMode, Slice};
+/// # let conn = Connection::connect("", &SslMode::None).unwrap();
+/// let values = &[1i32, 2, 3, 4, 5, 6];
+/// let stmt = try!(conn.prepare("SELECT * FROM foo WHERE id = ANY($1)"));
+/// for row in try!(stmt.query(&[&Slice(values)])) {
+///     // ...
+/// }
+/// # Ok(()) }
+/// ```
+pub struct Slice<'a, T: 'a + ToSql>(pub &'a [T]);
+
+impl<'a, T: 'a + ToSql> ToSql for Slice<'a, T> {
+    fn to_sql(&self, ty: &Type) -> Result<Option<Vec<u8>>> {
+        let member_type = match ty.element_type() {
+            Some(member) => member,
+            None => return Err(Error::WrongType(ty.clone())),
+        };
+
+        let mut buf = vec![];
+        let _ = buf.write_i32::<BigEndian>(1); // number of dimensions
+        let _ = buf.write_i32::<BigEndian>(1); // has nulls
+        let _ = buf.write_u32::<BigEndian>(member_type.to_oid());
+
+        let _ = buf.write_i32::<BigEndian>(self.0.len() as i32);
+        let _ = buf.write_i32::<BigEndian>(0); // index offset
+
+        for e in self.0 {
+            match try!(e.to_sql(&member_type)) {
+                Some(inner_buf) => {
+                    let _ = buf.write_i32::<BigEndian>(inner_buf.len() as i32);
+                    let _ = buf.write_all(&inner_buf);
+                }
+                None => {
+                    let _ = buf.write_i32::<BigEndian>(-1);
+                }
+            }
+        }
+
+        Ok(Some(buf))
+    }
+}

tests/types/mod.rs

@@ -6,7 +6,7 @@ use std::fmt;
 use std::num::Float;
 use std::old_io::net::ip::IpAddr;
 
-use postgres::{Connection, SslMode};
+use postgres::{Connection, SslMode, Slice, Error};
 use postgres::types::{ToSql, FromSql};
 
 #[cfg(feature = "uuid")]
@@ -223,3 +223,28 @@ fn test_pg_database_datname() {
     or_panic!(next.get_opt::<usize, String>(0));
     or_panic!(next.get_opt::<&str, String>("datname"));
 }
+
+#[test]
+fn test_slice() {
+    let conn = Connection::connect("postgres://postgres@localhost", &SslMode::None).unwrap();
+    conn.batch_execute("CREATE TEMPORARY TABLE foo (id SERIAL PRIMARY KEY, f VARCHAR);
+                        INSERT INTO foo (f) VALUES ('a'), ('b'), ('c'), ('d');").unwrap();
+
+    let stmt = conn.prepare("SELECT f FROM foo WHERE id = ANY($1)").unwrap();
+    let result = stmt.query(&[&Slice(&[1i32, 3, 4])]).unwrap();
+    assert_eq!(&["a".to_string(), "c".to_string(), "d".to_string()][],
+               result.map(|r| r.get::<_, String>(0)).collect::<Vec<_>>());
+}
+
+#[test]
+fn test_slice_wrong_type() {
+    let conn = Connection::connect("postgres://postgres@localhost", &SslMode::None).unwrap();
+    conn.batch_execute("CREATE TEMPORARY TABLE foo (id SERIAL PRIMARY KEY)").unwrap();
+
+    let stmt = conn.prepare("SELECT * FROM foo WHERE id = ANY($1)").unwrap();
+    match stmt.query(&[&Slice(&["hi"])]) {
+        Ok(_) => panic!("Unexpected success"),
+        Err(Error::WrongType(..)) => {}
+        Err(e) => panic!("Unexpected error {}", e),
+    }
+}