feat(bun): 🎉 Enhance nullability handling in column parsing

* Introduce explicit nullability markers in column tags.
* Update logic to infer nullability based on Go types when no markers are present.
* Ensure correct tags are generated for nullable and non-nullable fields.

pkg/readers/bun/reader.go

@@ -632,6 +632,9 @@ func (r *Reader) parseColumn(fieldName string, fieldType ast.Expr, tag string, s
 		column.Name = parts[0]
 	}
 
+	// Track if we found explicit nullability markers
+	hasExplicitNullableMarker := false
+
 	// Parse tag attributes
 	for _, part := range parts[1:] {
 		kv := strings.SplitN(part, ":", 2)
@@ -649,6 +652,10 @@ func (r *Reader) parseColumn(fieldName string, fieldType ast.Expr, tag string, s
 			column.IsPrimaryKey = true
 		case "notnull":
 			column.NotNull = true
+			hasExplicitNullableMarker = true
+		case "nullzero":
+			column.NotNull = false
+			hasExplicitNullableMarker = true
 		case "autoincrement":
 			column.AutoIncrement = true
 		case "default":
@@ -664,17 +671,15 @@ func (r *Reader) parseColumn(fieldName string, fieldType ast.Expr, tag string, s
 
 	// Determine if nullable based on Go type and bun tags
 	// In Bun:
-	// - nullzero tag means the field is nullable (can be NULL in DB)
-	// - absence of nullzero means the field is NOT NULL
-	// - primitive types (int64, bool, string) are NOT NULL by default
-	column.NotNull = true
-	// Primary keys are always NOT NULL
-
-	if strings.Contains(bunTag, "nullzero") {
-		column.NotNull = false
-	} else {
+	// - explicit "notnull" tag means NOT NULL
+	// - explicit "nullzero" tag means nullable
+	// - absence of explicit markers: infer from Go type
+	if !hasExplicitNullableMarker {
+		// Infer from Go type if no explicit marker found
 		column.NotNull = !r.isNullableGoType(fieldType)
 	}
+
+	// Primary keys are always NOT NULL
 	if column.IsPrimaryKey {
 		column.NotNull = true
 	}

pkg/writers/bun/type_mapper.go

@@ -192,8 +192,11 @@ func (tm *TypeMapper) BuildBunTag(column *models.Column, table *models.Table) st
 	}
 
 	// Nullable (Bun uses nullzero for nullable fields)
+	// and notnull tag for explicitly non-nullable fields
 	if !column.NotNull && !column.IsPrimaryKey {
 		parts = append(parts, "nullzero")
+	} else if column.NotNull && !column.IsPrimaryKey {
+		parts = append(parts, "notnull")
 	}
 
 	// Check for indexes (unique indexes should be added to tag)