fix: use Value-based binding in UpdateForm for proper Option<T> handling

When UpdateForm wraps fields that are already Option<T>, it creates
nested Options (Option<Option<T>>). The old bind_form_values method
bound these directly as &Option<T>, which caused MySQL "malform packet"
errors for Uuid -> BINARY(16) conversions.

Now both bind_form_values and bind_all_values use update_stmt_with_values()
which properly converts values through the Value enum:
- Some(None) -> Value::Null
- Some(Some(v)) -> Value::T(v)

This preserves the three-state semantics:
- None: don't include field in UPDATE
- Some(None): SET column = NULL
- Some(Some(v)): SET column = value

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.toml

@@ -5,7 +5,7 @@ edition.workspace = true
 description = "Entity CRUD and change tracking for SQL databases with SQLx"
 
 [workspace.package]
-version = "0.3.6"
+version = "0.3.7"
 edition = "2021"
 
 [dependencies]

sqlx-record-derive/src/lib.rs

@@ -1106,40 +1106,31 @@ fn generate_update_impl(
 
             /// Bind all form values to query in correct order.
             /// Handles both simple values and expression values, respecting expression precedence.
+            /// Uses Value enum for proper type handling of Option<T> fields.
             pub fn bind_all_values<'q>(&'q self, mut query: sqlx::query::Query<'q, #db, #db_args>)
                 -> sqlx::query::Query<'q, #db, #db_args>
             {
-                #(
-                    // Expression takes precedence over simple value
-                    if let Some(expr) = self._exprs.get(#db_names) {
-                        let (_, expr_values) = expr.build_sql(#db_names, 1);
-                        for value in expr_values {
+                // Use update_stmt_with_values to get properly converted values
+                // This handles nested Options (Option<Option<T>>) correctly
+                let (_, values) = self.update_stmt_with_values();
+                for value in values {
                     query = ::sqlx_record::prelude::bind_value_owned(query, value);
                 }
-                    } else if let Some(ref value) = self.#field_idents {
-                        query = query.bind(value);
-                    }
-                )*
                 query
             }
 
-            /// Legacy binding method - only binds simple Option values (ignores expressions).
+            /// Legacy binding method - binds values through the Value enum for proper type handling.
             /// For backward compatibility. New code should use bind_all_values().
             pub fn bind_form_values<'q>(&'q self, mut query: sqlx::query::Query<'q, #db, #db_args>)
                 -> sqlx::query::Query<'q, #db, #db_args>
             {
-                if self._exprs.is_empty() {
-                    // No expressions, use simple binding
-                    #(
-                        if let Some(ref value) = self.#field_idents {
-                            query = query.bind(value);
+                // Always use Value-based binding to properly handle Option<T> fields
+                // This ensures nested Options (Option<Option<T>>) are unwrapped correctly
+                let (_, values) = self.update_stmt_with_values();
+                for value in values {
+                    query = ::sqlx_record::prelude::bind_value_owned(query, value);
                 }
-                    )*
                 query
-                } else {
-                    // Has expressions, use full binding
-                    self.bind_all_values(query)
-                }
             }
 
             /// Check if this form uses any expressions

src/value.rs

@@ -256,6 +256,7 @@ impl UpdateExpr {
 pub type SqlValue = Value;
 
 // MySQL supports unsigned integers natively
+// Note: UUID is bound as bytes for BINARY(16) column compatibility
 #[cfg(feature = "mysql")]
 macro_rules! bind_value {
     ($query:expr, $value: expr) => {{