sqlite: Add basic json implementation

Fixes #608

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

@@ -0,0 +1,44 @@
+use serde::{Deserialize, Serialize};
+
+use crate::decode::Decode;
+use crate::encode::{Encode, IsNull};
+use crate::error::BoxDynError;
+use crate::sqlite::{
+    type_info::DataType, Sqlite, SqliteArgumentValue, SqliteTypeInfo, SqliteValueRef,
+};
+use crate::types::{Json, Type};
+
+impl<T> Type<Sqlite> for Json<T> {
+    fn type_info() -> SqliteTypeInfo {
+        SqliteTypeInfo(DataType::Text)
+    }
+
+    fn compatible(ty: &SqliteTypeInfo) -> bool {
+        <&str as Type<Sqlite>>::compatible(ty)
+    }
+}
+
+impl<T> Encode<'_, Sqlite> for Json<T>
+where
+    T: Serialize,
+{
+    fn encode_by_ref(&self, buf: &mut Vec<SqliteArgumentValue<'_>>) -> IsNull {
+        let json_string_value =
+            serde_json::to_string(&self.0).expect("serde_json failed to convert to string");
+
+        Encode::<Sqlite>::encode(json_string_value, buf)
+    }
+}
+
+impl<'r, T> Decode<'r, Sqlite> for Json<T>
+where
+    T: 'r + Deserialize<'r>,
+{
+    fn decode(value: SqliteValueRef<'r>) -> Result<Self, BoxDynError> {
+        let string_value = <&str as Decode<Sqlite>>::decode(value)?;
+
+        serde_json::from_str(&string_value)
+            .map(Json)
+            .map_err(Into::into)
+    }
+}

sqlx-core/src/sqlite/types/mod.rs

@@ -35,4 +35,6 @@ mod bytes;
 mod chrono;
 mod float;
 mod int;
+#[cfg(feature = "json")]
+mod json;
 mod str;