refine docs

Signed-off-by: Bugen Zhao <[email protected]>

src/meta/model/migration/src/utils.rs

@@ -4,6 +4,10 @@ use sea_orm_migration::prelude::*;
 #[easy_ext::ext(ColumnDefExt)]
 impl ColumnDef {
     /// Set column type as `longblob` for MySQL, `bytea` for Postgres, and `blob` for Sqlite.
+    ///
+    /// Should be preferred over [`binary`](ColumnDef::binary) or [`blob`](ColumnDef::blob) for large binary fields,
+    /// typically the fields wrapping protobuf or other serialized data. Otherwise, MySQL will return an error
+    /// when the length exceeds 65535 bytes.
     pub fn rw_binary(&mut self, manager: &SchemaManager) -> &mut Self {
         match manager.get_database_backend() {
             DatabaseBackend::MySql => self.custom(extension::mysql::MySqlType::LongBlob),