derive FromRow: sqlx(default) for all fields (#2801)

* derive FromRow: sqlx(default) for all fields

* error in test_struct_default fixed

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

* Update sqlx-core/src/from_row.rs

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

* Update sqlx-core/src/from_row.rs

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

* satify cargo fmt

---------

Co-authored-by: Austin Bonander <austin.bonander@gmail.com>

sqlx-core/src/from_row.rs

@@ -91,6 +91,26 @@ 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 the struct has an implementation for [`Default`], you can use the `default``
+/// attribute at the struct level rather than for each single field. If a field does not appear in the result,
+/// its value is taken from the `Default` implementation for the struct.
+/// For example:
+///
+/// ```rust, ignore
+/// #[derive(Default, sqlx::FromRow)]
+/// #[sqlx(default)]
+/// struct Options {
+///     option_a: Option<i32>,
+///     option_b: Option<String>,
+///     option_c: Option<bool>,
+/// }
+/// ```
+///
+/// For a derived `Default` implementation this effectively populates each missing field
+/// with `Default::default()`, but a manual `Default` implementation can provide
+/// different placeholder values, if applicable.
+///
+/// This is similar to how `#[serde(default)]` behaves.
 /// ### `flatten`
 ///
 /// If you want to handle a field that implements [`FromRow`],

sqlx-macros-core/src/derives/attributes.rs

@@ -57,6 +57,7 @@ pub struct SqlxContainerAttributes {
     pub rename_all: Option<RenameAll>,
     pub repr: Option<Ident>,
     pub no_pg_array: bool,
+    pub default: bool,
 }
 
 pub struct SqlxChildAttributes {
@@ -74,6 +75,7 @@ pub fn parse_container_attributes(input: &[Attribute]) -> syn::Result<SqlxContai
     let mut type_name = None;
     let mut rename_all = None;
     let mut no_pg_array = None;
+    let mut default = None;
 
     for attr in input
         .iter()
@@ -129,6 +131,10 @@ pub fn parse_container_attributes(input: &[Attribute]) -> syn::Result<SqlxContai
                                 )
                             }
 
+                            Meta::Path(p) if p.is_ident("default") => {
+                                try_set!(default, true, value)
+                            }
+
                             u => fail!(u, "unexpected attribute"),
                         },
                         u => fail!(u, "unexpected attribute"),
@@ -156,6 +162,7 @@ pub fn parse_container_attributes(input: &[Attribute]) -> syn::Result<SqlxContai
         type_name,
         rename_all,
         no_pg_array: no_pg_array.unwrap_or(false),
+        default: default.unwrap_or(false),
     })
 }
 

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> {
@@ -148,6 +159,13 @@ fn expand_derive_from_row_struct(
                 },
                 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 {

tests/postgres/derives.rs

@@ -621,6 +621,41 @@ async fn test_default() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[cfg(feature = "macros")]
+#[sqlx_macros::test]
+async fn test_struct_default() -> anyhow::Result<()> {
+    #[derive(Debug, sqlx::FromRow)]
+    #[sqlx(default)]
+    struct HasDefault {
+        not_default: Option<i32>,
+        default_a: Option<String>,
+        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"#)
+        .fetch_one(&mut conn)
+        .await?;
+    println!("{has_default:?}");
+
+    assert_eq!(has_default.not_default, Some(1));
+    assert_eq!(has_default.default_a, None);
+    assert_eq!(has_default.default_b, Some(0));
+
+    Ok(())
+}
+
 #[cfg(feature = "macros")]
 #[sqlx_macros::test]
 async fn test_flatten() -> anyhow::Result<()> {