derive FromRow: struct level sqlx(default) requires and uses Default …

…implementation
launchbadge · Oct 8, 2023 · bbe1eaa · bbe1eaa
1 parent 4f4f57c
commit bbe1eaa
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Showing 3 changed files with 36 additions and 5 deletions.
diff --git a/sqlx-core/src/from_row.rs b/sqlx-core/src/from_row.rs
@@ -91,12 +91,13 @@ use crate::{error::Error, row::Row};
 /// will set the value of the field `location` to the default value of `Option<String>`,
 /// which is `None`.
 ///
-/// Moreover, if all field types have an implementation for [`Default`], you can use the `default``
-/// attribute at the struct level rather than each single field.
+/// Moreover, if the struct has an implementation for [`Default`], you can use the `default``
+/// attribute at the struct level rather than for each single field. This way the default
+/// value of each attribute is optained from the particular `Default` implementation.
 /// For example:
 ///
 /// ```rust, ignore
-/// #[derive(sqlx::FromRow)]
+/// #[derive(Default, sqlx::FromRow)]
 /// #[sqlx(default)]
 /// struct Options {
 ///     option_a: Option<i32>,

diff --git a/sqlx-macros-core/src/derives/row.rs b/sqlx-macros-core/src/derives/row.rs
@@ -65,6 +65,17 @@ fn expand_derive_from_row_struct(
 
     let container_attributes = parse_container_attributes(&input.attrs)?;
 
+    let default_instance: Option<Stmt>;
+
+    if container_attributes.default {
+        predicates.push(parse_quote!(#ident: ::std::default::Default));
+        default_instance = Some(parse_quote!(
+            let __default = #ident::default();
+        ));
+    } else {
+        default_instance = None;
+    }
+
     let reads: Vec<Stmt> = fields
         .iter()
         .filter_map(|field| -> Option<Stmt> {
@@ -141,13 +152,20 @@ fn expand_derive_from_row_struct(
                 },
             };
 
-            if attributes.default || container_attributes.default {
+            if attributes.default {
                 Some(parse_quote!(let #id: #ty = #expr.or_else(|e| match e {
                 ::sqlx::Error::ColumnNotFound(_) => {
                     ::std::result::Result::Ok(Default::default())
                 },
                 e => ::std::result::Result::Err(e)
             })?;))
+            } else if container_attributes.default {
+                Some(parse_quote!(let #id: #ty = #expr.or_else(|e| match e {
+                    ::sqlx::Error::ColumnNotFound(_) => {
+                        ::std::result::Result::Ok(__default.#id)
+                    },
+                    e => ::std::result::Result::Err(e)
+                })?;))
             } else {
                 Some(parse_quote!(
                     let #id: #ty = #expr?;
@@ -164,6 +182,8 @@ fn expand_derive_from_row_struct(
         #[automatically_derived]
         impl #impl_generics ::sqlx::FromRow<#lifetime, R> for #ident #ty_generics #where_clause {
             fn from_row(row: &#lifetime R) -> ::sqlx::Result<Self> {
+                #default_instance
+
                 #(#reads)*
 
                 ::std::result::Result::Ok(#ident {

diff --git a/tests/postgres/derives.rs b/tests/postgres/derives.rs
@@ -632,6 +632,16 @@ async fn test_struct_default() -> anyhow::Result<()> {
         default_b: Option<i32>,
     }
 
+    impl Default for HasDefault {
+        fn default() -> HasDefault {
+            HasDefault {
+                not_default: None,
+                default_a: None,
+                default_b: Some(0),
+            }
+        }
+    }
+
     let mut conn = new::<Postgres>().await?;
 
     let has_default: HasDefault = sqlx::query_as(r#"SELECT 1 AS not_default"#)
@@ -641,7 +651,7 @@ async fn test_struct_default() -> anyhow::Result<()> {
 
     assert_eq!(has_default.not_default, Some(1));
     assert_eq!(has_default.default_a, None);
-    assert_eq!(has_default.default_b, None);
+    assert_eq!(has_default.default_b, Some(0));
 
     Ok(())
 }