Module patch 

Shared “double Option” (de)serialization for Update{Model}Input fields that back a nullable column — see cratestack#567.

Update{Model}Input wraps every field in an outer Option<T> (“was this field touched by this patch at all”) on top of whatever the column’s own nullability already contributes. For a nullable column that’s a second, independent Option layer: None (field omitted), Some(None) (field explicitly set to SQL NULL), Some(Some(v)) (field set to v). serde-derive’s blanket Option<T>: Deserialize only ever peels one layer — a JSON/CBOR null and an absent key both collapse to the outer None via visit_none(), so Some(None) was never reachable over the wire and “clear this column” silently did nothing (update_sql_value skips a None field).

deserialize_double_option is the fix for the inbound side: paired with #[serde(default, ...)] (required because a custom deserialize_with opts a field out of serde-derive’s own implicit “missing Option<T> field defaults to None” handling), it recurses into the inner Option instead of stopping at the outer one.

The outbound side needs an equally deliberate fix, not just the inverse of this function: Update{Model}Input’s derived Serialize has no custom logic at all, so an untouched field (outer None) is not omitted from the wire by default — it serializes as null, identical to an explicit clear. Every generated caller (the Rust/Dart/ TypeScript HTTP clients) builds a full Update{Model}Input with ..Default::default() for untouched fields and serializes the whole struct, so without a fix here every partial update over those clients would start nulling out every field it didn’t set the moment deserialize_double_option made the server actually honour null as “clear”. The generated field attribute pairs this function with #[serde(skip_serializing_if = "Option::is_none")] on the outer Option, so an untouched field is omitted from the wire entirely (never sent as null) and only Some(_) — a field this patch genuinely touches — is serialized at all.

Functions

deserialize_double_option

Deserializes Option<Option<T>> distinguishing “key absent” from “key present with value null”. Pair with #[serde(default, ...)] — see the module doc for why default is required once a field opts into a custom deserialize_with.