RUST-1987 Add serde helper module for Option<DateTime> (#482)

Author: lazureykis

src/serde_helpers.rs

@@ -17,6 +17,12 @@ pub use chrono_datetime_as_bson_datetime::{
     deserialize as deserialize_chrono_datetime_from_bson_datetime,
     serialize as serialize_chrono_datetime_as_bson_datetime,
 };
+#[cfg(feature = "chrono-0_4")]
+#[doc(inline)]
+pub use chrono_datetime_as_bson_datetime_optional::{
+    deserialize as deserialize_chrono_datetime_from_bson_datetime_optional,
+    serialize as serialize_chrono_datetime_as_bson_datetime_optional,
+};
 #[doc(inline)]
 pub use hex_string_as_object_id::{
     deserialize as deserialize_hex_string_from_object_id,
@@ -307,6 +313,51 @@ pub mod chrono_datetime_as_bson_datetime {
     }
 }
 
+/// Contains functions to serialize an [`Option<chrono::DateTime>`] as an
+/// [`Option<crate::DateTime>`] and deserialize an [`Option<chrono::DateTime>`] from an
+/// [`Option<crate::DateTime>`].
+///
+/// ```rust
+/// # #[cfg(feature = "chrono-0_4")]
+/// # {
+/// # use serde::{Serialize, Deserialize};
+/// # use bson::serde_helpers::chrono_datetime_as_bson_datetime_optional;
+/// #[derive(Serialize, Deserialize)]
+/// struct Event {
+///     #[serde(with = "chrono_datetime_as_bson_datetime_optional")]
+///     pub date: Option<chrono::DateTime<chrono::Utc>>,
+/// }
+/// # }
+/// ```
+#[cfg(feature = "chrono-0_4")]
+#[cfg_attr(docsrs, doc(cfg(feature = "chrono-0_4")))]
+pub mod chrono_datetime_as_bson_datetime_optional {
+    use crate::DateTime;
+    use chrono::Utc;
+    use serde::{Deserialize, Deserializer, Serialize, Serializer};
+    use std::result::Result;
+
+    /// Deserializes a [`chrono::DateTime`] from a [`crate::DateTime`].
+    #[cfg_attr(docsrs, doc(cfg(feature = "chrono-0_4")))]
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<Option<chrono::DateTime<Utc>>, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let val = Option::deserialize(deserializer)?.map(|datetime: DateTime| datetime.to_chrono());
+        Ok(val)
+    }
+
+    /// Serializes a [`Option<chrono::DateTime>`] as a [`Option<crate::DateTime>`].
+    #[cfg_attr(docsrs, doc(cfg(feature = "chrono-0_4")))]
+    pub fn serialize<S: Serializer>(
+        val: &Option<chrono::DateTime<Utc>>,
+        serializer: S,
+    ) -> Result<S::Ok, S::Error> {
+        let datetime = val.map(DateTime::from_chrono);
+        datetime.serialize(serializer)
+    }
+}
+
 /// Contains functions to serialize an RFC 3339 (ISO 8601) formatted string as a [`crate::DateTime`]
 /// and deserialize an RFC 3339 (ISO 8601) formatted string from a [`crate::DateTime`].
 ///

src/tests/serde.rs

@@ -866,6 +866,59 @@ fn test_datetime_helpers() {
         assert_eq!(b.date, expected);
     }
 
+    #[cfg(feature = "chrono-0_4")]
+    {
+        use std::str::FromStr;
+        #[derive(Deserialize, Serialize)]
+        struct B {
+            #[serde(with = "serde_helpers::chrono_datetime_as_bson_datetime_optional")]
+            pub date: Option<chrono::DateTime<chrono::Utc>>,
+        }
+
+        let date = r#"
+    {
+        "date": {
+                "$date": {
+                    "$numberLong": "1591700287095"
+                }
+        }
+    }"#;
+        let json: serde_json::Value = serde_json::from_str(date).unwrap();
+        let b: B = serde_json::from_value(json).unwrap();
+        let expected: Option<chrono::DateTime<chrono::Utc>> =
+            Some(chrono::DateTime::from_str("2020-06-09 10:58:07.095 UTC").unwrap());
+        assert_eq!(b.date, expected);
+        let doc = to_document(&b).unwrap();
+        assert_eq!(
+            Some(doc.get_datetime("date").unwrap().to_chrono()),
+            expected
+        );
+        let b: B = from_document(doc).unwrap();
+        assert_eq!(b.date, expected);
+    }
+
+    #[cfg(feature = "chrono-0_4")]
+    {
+        #[derive(Deserialize, Serialize)]
+        struct B {
+            #[serde(with = "serde_helpers::chrono_datetime_as_bson_datetime_optional")]
+            pub date: Option<chrono::DateTime<chrono::Utc>>,
+        }
+
+        let date = r#"
+    {
+        "date": null
+    }"#;
+        let json: serde_json::Value = serde_json::from_str(date).unwrap();
+        let b: B = serde_json::from_value(json).unwrap();
+        let expected = None;
+        assert_eq!(b.date, expected);
+        let doc = to_document(&b).unwrap();
+        assert_eq!(None, expected);
+        let b: B = from_document(doc).unwrap();
+        assert_eq!(b.date, expected);
+    }
+
     #[derive(Deserialize, Serialize)]
     struct C {
         #[serde(with = "rfc3339_string_as_bson_datetime")]