feat: Implement custom handling for Option<T> in ODBC arguments

This commit adds a custom implementation for encoding and decoding Option<T> types in the ODBC arguments module. It enhances the handling of null values by allowing for proper encoding of optional parameters, ensuring compatibility with the ODBC API. Additionally, a new test is introduced to verify the binding of null string parameters in SQL queries.

Author: lovasoa

sqlx-core/src/odbc/arguments.rs

@@ -8,6 +8,7 @@ pub struct OdbcArguments<'q> {
     pub(crate) values: Vec<OdbcArgumentValue<'q>>,
 }
 
+#[derive(Debug, Clone)]
 pub enum OdbcArgumentValue<'q> {
     Text(String),
     Bytes(Vec<u8>),
@@ -116,3 +117,40 @@ impl<'q> Encode<'q, Odbc> for Vec<u8> {
         crate::encode::IsNull::No
     }
 }
+
+impl<'q, T> Encode<'q, Odbc> for Option<T>
+where
+    T: Encode<'q, Odbc> + Type<Odbc> + 'q,
+{
+    fn produces(&self) -> Option<crate::odbc::OdbcTypeInfo> {
+        if let Some(v) = self {
+            v.produces()
+        } else {
+            T::type_info().into()
+        }
+    }
+
+    fn encode(self, buf: &mut Vec<OdbcArgumentValue<'q>>) -> crate::encode::IsNull {
+        match self {
+            Some(v) => v.encode(buf),
+            None => {
+                buf.push(OdbcArgumentValue::Null);
+                crate::encode::IsNull::Yes
+            }
+        }
+    }
+
+    fn encode_by_ref(&self, buf: &mut Vec<OdbcArgumentValue<'q>>) -> crate::encode::IsNull {
+        match self {
+            Some(v) => v.encode_by_ref(buf),
+            None => {
+                buf.push(OdbcArgumentValue::Null);
+                crate::encode::IsNull::Yes
+            }
+        }
+    }
+
+    fn size_hint(&self) -> usize {
+        self.as_ref().map_or(0, Encode::size_hint)
+    }
+}

sqlx-core/src/odbc/connection/worker.rs

@@ -265,7 +265,7 @@ fn execute_sql_with_params(
 
     let mut params: Vec<Box<dyn odbc_api::parameter::InputParameter>> =
         Vec::with_capacity(args.len());
-    for a in args {
+    for a in dbg!(args) {
         params.push(to_param(a));
     }
     dispatch_execute(conn, sql, &params[..], tx);
@@ -280,7 +280,7 @@ fn to_param(
         OdbcArgumentValue::Text(s) => Box::new(s.into_parameter()),
         OdbcArgumentValue::Bytes(b) => Box::new(b.into_parameter()),
         OdbcArgumentValue::Null | OdbcArgumentValue::Phantom(_) => {
-            Box::new(Option::<i32>::None.into_parameter())
+            Box::new(Option::<String>::None.into_parameter())
         }
     }
 }

sqlx-core/src/odbc/mod.rs

@@ -47,5 +47,4 @@ impl_column_index_for_statement!(OdbcStatement);
 impl_acquire!(Odbc, OdbcConnection);
 impl_into_maybe_pool!(Odbc, OdbcConnection);
 
-// required because some databases have a different handling of NULL
-impl_encode_for_option!(Odbc);
+// custom Option<..> handling implemented in `arguments.rs`

tests/odbc/odbc.rs

@@ -210,3 +210,21 @@ async fn it_can_bind_heterogeneous_params() -> anyhow::Result<()> {
     assert_eq!(last, 42);
     Ok(())
 }
+
+#[tokio::test]
+async fn it_binds_null_string_parameter() -> anyhow::Result<()> {
+    let mut conn = new::<Odbc>().await?;
+    let stmt = (&mut conn).prepare("SELECT ?, ?").await?;
+    let row = stmt
+        .query()
+        .bind("abc")
+        .bind(Option::<String>::None)
+        .fetch_one(&mut conn)
+        .await?;
+
+    let a = row.try_get_raw(0)?.to_owned().decode::<String>();
+    let b = row.try_get_raw(1)?.to_owned();
+    assert_eq!(a, "abc");
+    assert!(b.is_null());
+    Ok(())
+}