fix insert on conflict do nothing

core/src/insert.rs

@@ -1,8 +1,7 @@
 use crate::Result;
 use futures::future::BoxFuture;
 pub use sqlmo::query::OnConflict;
-#[allow(unused_imports)]
-use sqlmo::{Dialect, Insert, ToSql};
+use sqlmo::{Dialect, Insert, ToSql, Union, Select, Cte, SelectColumn};
 
 /// Represents an insert query.
 /// We had to turn this into a model because we need to pass in the on_conflict configuration.
@@ -28,7 +27,36 @@ impl<'a, Acquire, Model: crate::model::Model<DB>, DB: sqlx::Database> std::futur
     type IntoFuture = BoxFuture<'a, Self::Output>;
 
     fn into_future(self) -> Self::IntoFuture {
-        let q = self.insert.to_sql(Dialect::Postgres);
+        // hack to get around the fact that postgres drops the return
+        // value in ON CONFLICT DO NOTHING case
+        let q = if matches!(self.insert.on_conflict, OnConflict::Ignore) {
+            let insert_as_select = Select {
+                ctes: vec![
+                    Cte::new("inserted", self.insert)
+                ],
+                columns: vec![SelectColumn::raw("*")],
+                from: Some("inserted".into()),
+                ..Select::default()
+            };
+            let pkey = Model::primary_key().unwrap();
+            let plc_idx = Model::primary_key_placeholder_idx().unwrap();
+            let select_existing = Select {
+                from: Some(Model::table_name().into()),
+                columns: Model::table_columns().iter().map(|&c| c.into()).collect(),
+                where_: format!("{pkey} = ${plc_idx}").into(),
+                ..Select::default()
+            };
+            let union = Union {
+                all: true,
+                queries: vec![
+                    insert_as_select,
+                    select_existing
+                ]
+            };
+            union.to_sql(Dialect::Postgres)
+        } else {
+            self.insert.to_sql(Dialect::Postgres)
+        };
         (self.closure)(self.acquire, self.model, q)
     }
 }

core/src/model.rs

@@ -109,4 +109,8 @@ pub trait TableMeta {
     fn table_name() -> &'static str;
     fn table_columns() -> &'static [&'static str];
     fn primary_key() -> Option<&'static str>;
+    fn primary_key_placeholder_idx() -> Option<usize> {
+        let col = Self::primary_key()?;
+        Self::table_columns().iter().position(|&c| c == col).map(|i| i + 1)
+    }
 }