[dagster-pipes-rust] 🔥 Simplify PipesMetadataValue construction

[christeefy]

Summary & Motivation

Fixes #46.

Approach

• Utilize Rust's From<T> trait wherever possible, allowing native types to be converted using PipesMetadataValue::from(10). This has been implemented for f64, i64, bool, String, HashMap and Vec.
• For types that don't derive directly from a native type (e.g. dagster_run, timestamp, null), a ::from_* method is used instead. For example, PipesMetadataValue::from_asset("my_asset").

Alternatives Considered: Use of Custom Types

The RawValue and Type enums from jsonschema have implicit connections to each other (e.g. Type::Int should have a RawValue::Integer(...), and nothing else). Currently users are responsible for knowing this implicit mapping.

I thought of using user-facing, custom MetadataValue enum that is separately defined from jsonschema. This MetadataValue (different from PipesMetadata) is responsible for

1. encoding the relationships between RawValue and Type
2. mapping user-facing inputs over to PipesMetadataValue, RawValue and Type.

Something as follows:

pub enum MetadataValue {
    Asset(String),
    Bool(bool),
    ...
}

impl From<MetadataValue> for PipesMetadata { ... }

// main.rs
HashMap::from([("asset", MetadataValue::Asset("my_asset").into()])

In the end, the idea was scrapped because it introduces another enum that is very similar to existing public jsonschema types.

How I Tested These Changes

• cargo nextest and no errors from compiler

Changelog

Ensure that an entry has been created in CHANGELOG.md outlining additions, deletions, and/or modifications.

See: keepachangelog.com

[marijncv]

Really nice!

[christeefy]

What do you think about this method name? Should it be none, from_none, or null?

[christeefy]

And should this be None, or Some(Type::Null)? Not sure what's the difference with either option though.

[marijncv]

I would go with:

    pub fn null() -> Self {
        PipesMetadataValue {
            raw_value: None,
            pipes_metadata_value_type: Some(Type::Null),

Function name: null is similar to the python implementation here. Some(Type::Null) follows the convention used by the other types in the rust implementation

[christeefy]

Done! Will merge in an hour, if everything's still looks good.

[marijncv]

LGTM!