json: Refactor Encode/Decode for serde values to be generic for DB

Since the implementation of Encode and Decode for both mysql and
postgres on serde's Value and RawValue were practically the same they
were moved to the generic json module.

sqlx-core/src/mysql/types/json.rs

@@ -14,18 +14,6 @@ impl Type<MySql> for JsonValue {
     }
 }
 
-impl Encode<MySql> for JsonValue {
-    fn encode(&self, buf: &mut Vec<u8>) {
-        (Box::new(Json(self)) as Box<dyn Encode<MySql>>).encode(buf)
-    }
-}
-
-impl<'de> Decode<'de, MySql> for JsonValue {
-    fn decode(value: MySqlValue<'de>) -> crate::Result<Self> {
-        <Json<Self> as Decode<MySql>>::decode(value).map(|item| item.0)
-    }
-}
-
 impl<T> Type<MySql> for Json<T> {
     fn type_info() -> MySqlTypeInfo {
         // MySql uses the CHAR type to pass JSON data from and to the client

sqlx-core/src/postgres/types/json.rs

@@ -21,36 +21,12 @@ impl Type<Postgres> for JsonValue {
     }
 }
 
-impl Encode<Postgres> for JsonValue {
-    fn encode(&self, buf: &mut PgRawBuffer) {
-        (Box::new(Json(self)) as Box<dyn Encode<Postgres>>).encode(buf)
-    }
-}
-
-impl<'de> Decode<'de, Postgres> for JsonValue {
-    fn decode(value: PgValue<'de>) -> crate::Result<Self> {
-        <Json<Self> as Decode<Postgres>>::decode(value).map(|item| item.0)
-    }
-}
-
 impl Type<Postgres> for &'_ JsonRawValue {
     fn type_info() -> PgTypeInfo {
         <Json<Self> as Type<Postgres>>::type_info()
     }
 }
 
-impl Encode<Postgres> for &'_ JsonRawValue {
-    fn encode(&self, buf: &mut PgRawBuffer) {
-        (Box::new(Json(self)) as Box<dyn Encode<Postgres>>).encode(buf)
-    }
-}
-
-impl<'de> Decode<'de, Postgres> for &'de JsonRawValue {
-    fn decode(value: PgValue<'de>) -> crate::Result<Self> {
-        <Json<Self> as Decode<Postgres>>::decode(value).map(|item| item.0)
-    }
-}
-
 impl<T> Type<Postgres> for Json<T> {
     fn type_info() -> PgTypeInfo {
         PgTypeInfo::new(TypeId::JSONB, "JSONB")

sqlx-core/src/types.rs

@@ -43,6 +43,12 @@ pub mod ipnetwork {
 
 #[cfg(feature = "json")]
 pub mod json {
+    use crate::database::Database;
+    use crate::decode::Decode;
+    use crate::encode::Encode;
+    use crate::value::HasRawValue;
+    use serde_json::value::RawValue as JsonRawValue;
+    use serde_json::Value as JsonValue;
     use std::ops::Deref;
 
     #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
@@ -62,6 +68,38 @@ pub mod json {
             &self.0
         }
     }
+
+    impl<DB> Encode<DB> for JsonValue
+    where
+        Json<Self>: Encode<DB>,
+        DB: Database,
+    {
+        fn encode(&self, buf: &mut DB::RawBuffer) {
+            <Json<Self> as Encode<DB>>::encode(&Json(self.clone()), buf)
+        }
+    }
+
+    impl<'de, DB> Decode<'de, DB> for JsonValue
+    where
+        Json<Self>: Decode<'de, DB>,
+        DB: Database,
+    {
+        fn decode(value: <DB as HasRawValue<'de>>::RawValue) -> crate::Result<Self> {
+            <Json<Self> as Decode<DB>>::decode(value).map(|item| item.0)
+        }
+    }
+
+    // We don't have to implement Encode for JsonRawValue because that's covered by the default
+    // implementation for Encode
+    impl<'de, DB> Decode<'de, DB> for &'de JsonRawValue
+    where
+        Json<Self>: Decode<'de, DB>,
+        DB: Database,
+    {
+        fn decode(value: <DB as HasRawValue<'de>>::RawValue) -> crate::Result<Self> {
+            <Json<Self> as Decode<DB>>::decode(value).map(|item| item.0)
+        }
+    }
 }
 #[cfg(feature = "json")]
 pub use self::json::Json;