Unable to (de)serialize nested JSON Blobs using serde Traits

[mara-schulke]

Description

We have a database schema where we save (from the db pov) untyped json blobs into the database + some metadata columns. We have a serde compatible struct for describing the blobs on the rust side and expected to be able to use the #[sea_orm(db_type = "Json")] as annotation to be able to deserialize the JSON col into the rust struct on select.

Steps to Reproduce

Rust

use some_external_crate::priding::our::type::SomeStruct;
use sea_orm::entity::prelude::*;
use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, Deserialize, Serialize, Eq, PartialEq, DeriveEntityModel)]
#[sea_orm(table_name = "table_name")]
pub struct Model {
    #[sea_orm(primary_key)]
    pub id: String,
    #[sea_orm(db_type = "Json")]
    pub details: SomeStruct,
    pub refreshed_at: DateTime,
}

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {}

...

SQL

CREATE TABLE table_name (
    id varchar(64) PRIMARY KEY,
    refreshed_at   timestamptz NOT NULL,
    details        jsonb NOT NULL
);

Expected Behavior

The details field of the Model should be deserialized from json / jsonb columns into the SomeStruct type in rust.

Actual Behavior

"the trait bound `sea_orm::Value: From<SomeStruct>` is not satisfied"

Reproduces How Often

Every time.

Versions

0.7.1

Additional Information

None

[billy1624]

Hey @schulke-214, please refer to https://github.com/SeaQL/sea-orm/blob/master/issues/400/src/model.rs on how to implement necessary traits for custom model fields

[mara-schulke]

It comes from an external crate. We are unable to implement your traits for external types. Also i would expect sea-orm to be compliant with standard rust ecosystem traits such as Serialize and Deserialize instead of building your own type infrastructure around it. Most crates wont be compatible with sea orm this way.

[billy1624]

This isn't ideal but you can do it with newtype pattern.

pub struct MySomeStruct(SomeStruct);

impl SomeTrait for MySomeStruct {
    ...
}

[mara-schulke]

If that is the only reaction to this issue we are not going to be able to use sea orm sadly. I think a lot of things are done excellent about it, but this is just some missing trait implementations on your side:

https://github.com/SeaQL/sea-query/blob/master/src/value.rs#L304-L308

mod with_json {
    ...
 
    impl<T> From<T> for sea_orm::Value
    where
        T: Serialize,
        for<'de> T: Deserialize<'de>
    {
        fn from(json: T) -> Self {
            if let Some(value) = serde_json::to_value(&json) {
                return Self::Value::Json(Some(Box::new(value))
            }

            None
        }
    }


    impl<T> Nullable for T
    where
        T: Serialize,
        for<'de> T: Deserialize<'de>
    {
        fn null() -> Value {
            Value::Json(None)
        }
    }

    impl<T> ValueType for T
    where
        T: Serialize,
        for<'de> T: Deserialize<'de>
    {
        fn try_from(v: Value) -> Result<Self, ValueTypeErr> {
            match v {
                Value::Json(Some(x)) => serde_json::from_value(x.as_ref()),
                _ => Err(ValueTypeErr),
            }
        }

        fn type_name() -> String {
            "Json".to_owned()
        }

        fn column_type() -> ColumnType {
           // take smh from the annotation #[sea_orm(db_type="X")
        }
    }
} 

[tyt2y3]

@schulke-214 I think you raised an interesting use case
Can you open a PR on that code snippet you gave?
It'd also be great if we can add some test cases to tests/serde_json.rs so that it won't be broken in the future.

[billy1624]

Hey @schulke-214, feel free to review #696

[tyt2y3]

#696 (comment)