Implements fmt::Display for ActiveEnum (#986)

Co-authored-by: Chris Tsang <chris.2y3@outlook.com>

sea-orm-macros/src/derives/active_enum.rs

@@ -353,6 +353,14 @@ impl ActiveEnum {
                     <<Self as sea_orm::ActiveEnum>::Value as sea_orm::sea_query::Nullable>::null()
                 }
             }
+
+            #[automatically_derived]
+            impl std::fmt::Display for #ident {
+                fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                    let v: sea_orm::sea_query::Value = self.to_value().into();
+                    write!(f, "{}", v)
+                }
+            }
         )
     }
 }

src/entity/active_enum.rs

@@ -241,6 +241,9 @@ mod tests {
             DeriveCategory::name().to_string()
         );
         assert_eq!(Category::values(), DeriveCategory::values());
+
+        assert_eq!(format!("{}", DeriveCategory::Big), "'B'");
+        assert_eq!(format!("{}", DeriveCategory::Small), "'S'");
     }
 
     #[test]
@@ -295,6 +298,10 @@ mod tests {
                 );
 
                 assert_eq!($ident::db_type(), ColumnType::$col_def.def());
+
+                assert_eq!(format!("{}", $ident::Big), "1");
+                assert_eq!(format!("{}", $ident::Small), "0");
+                assert_eq!(format!("{}", $ident::Negative), "-10");
             };
         }
 
@@ -356,6 +363,9 @@ mod tests {
                 );
 
                 assert_eq!($ident::db_type(), ColumnType::$col_def.def());
+
+                assert_eq!(format!("{}", $ident::Big), "1");
+                assert_eq!(format!("{}", $ident::Small), "0");
             };
         }