influxdb-derive: add #[ignored] attribute

[blasrodri]

This attribute signals influx to avoid inserting a field

ref: #76

Description

{ describe your changes here }

Checklist

• [x ] Formatted code using cargo fmt --all
• [ x] Linted code using clippy cargo clippy --all-targets --all-features -- -D warnings
• [ x] Updated README.md using cargo readme -r influxdb -t ../README.tpl > README.md
• [ x] Reviewed the diff. Did you leave any print statements or unnecessary comments?
• [ x] Any unfinished work that warrants a separate issue captured in an issue with a TODO code comment

[msrd0]

I dislike introducing more attributes with names unrelated to influxdb - instead, I'd suggest we introduce one influxdb attribute and then use inner tags, like most other rust projects including serde do. The struct would then look something like this:

#[derive(InfluxDbWriteable)]
struct WeatherReadingIgnoredField {
    time: DateTime<Utc>,
    humidity: i32,
    #[influxdb(tag)]
    wind_strength: Option<u64>,
    #[influxdb(ignore)]
    temperature: u64,
}

This would however be a breaking change, whereas just adding another tag is a non-breaking change. We could also support both for a while, but (deprecation) warnings are not a thing until diagnostics are stabilized.

[Empty2k12]

I have no problems with breaking changes. We're well below 1.0 and therefore semantic stability cannot be guaranteed.

[blasrodri]

I dislike introducing more attributes with names unrelated to influxdb - instead, I'd suggest we introduce one influxdb attribute and then use inner tags, like most other rust projects including serde do. The struct would then look something like this:

#[derive(InfluxDbWriteable)]
struct WeatherReadingIgnoredField {
    time: DateTime<Utc>,
    humidity: i32,
    #[influxdb(tag)]
    wind_strength: Option<u64>,
    #[influxdb(ignore)]
    temperature: u64,
}

This would however be a breaking change, whereas just adding another tag is a non-breaking change. We could also support both for a while, but (deprecation) warnings are not a thing until diagnostics are stabilized.

I made an attempt here
Could you please review it and help me out? It's currently failing.

Thanks!

[blasrodri]

closing in favor of #81