feat(core): add ColumnIndex

sqlx-core/src/lib.rs

@@ -70,7 +70,7 @@ pub use isolation_level::IsolationLevel;
 pub use options::ConnectOptions;
 pub use query_result::QueryResult;
 pub use r#type::{Type, TypeDecode, TypeEncode};
-pub use row::Row;
+pub use row::{ColumnIndex, Row};
 #[cfg(feature = "actix")]
 pub use runtime::Actix;
 #[cfg(feature = "async")]

sqlx-core/src/row.rs

@@ -1,6 +1,7 @@
 use crate::database::HasRawValue;
 use crate::{Database, Decode};
 
+/// A single row from a result set generated from the database.
 pub trait Row: 'static + Send + Sync {
     type Database: Database;
 
@@ -31,18 +32,48 @@ pub trait Row: 'static + Send + Sync {
     fn try_ordinal_of(&self, name: &str) -> crate::Result<usize>;
 
     /// Returns the decoded value at the index.
-    fn try_get<'r, T>(&'r self, index: usize) -> crate::Result<T>
+    fn try_get<'r, T, I>(&'r self, index: I) -> crate::Result<T>
     where
+        I: ColumnIndex<Self>,
         T: Decode<'r, Self::Database>;
 
     /// Returns the raw representation of the value at the index.
     #[allow(clippy::needless_lifetimes)]
-    fn try_get_raw<'r>(
+    fn try_get_raw<'r, I: ColumnIndex<Self>>(
         &'r self,
-        index: usize,
+        index: I,
     ) -> crate::Result<<Self::Database as HasRawValue<'r>>::RawValue>;
 }
 
-// TODO: fn type_info_of(index)
-// TODO: fn try_type_info_of(index)
-// TODO: trait ColumnIndex
+/// A helper trait used for indexing into a [`Row`].
+pub trait ColumnIndex<R: Row + ?Sized> {
+    /// Returns the ordinal of the column at this index, if present.
+    #[allow(clippy::needless_lifetimes)]
+    fn get<'r>(&self, row: &'r R) -> crate::Result<usize>;
+}
+
+// access an ordinal by index
+impl<R: Row> ColumnIndex<R> for usize {
+    #[allow(clippy::needless_lifetimes)]
+    fn get<'r>(&self, _row: &'r R) -> crate::Result<usize> {
+        // note: the "index out of bounds" error will be surfaced
+        //  by [try_get]
+        Ok(*self)
+    }
+}
+
+// access an ordinal by name
+impl<R: Row> ColumnIndex<R> for &'_ str {
+    #[allow(clippy::needless_lifetimes)]
+    fn get<'r>(&self, row: &'r R) -> crate::Result<usize> {
+        row.try_ordinal_of(self)
+    }
+}
+
+// access by reference
+impl<R: Row, I: ColumnIndex<R>> ColumnIndex<R> for &'_ I {
+    #[allow(clippy::needless_lifetimes)]
+    fn get<'r>(&self, row: &'r R) -> crate::Result<usize> {
+        (*self).get(row)
+    }
+}