`ctx.timestamp` for views - to query for `last_updated`.

[luckydonald]

I'm trying to create a view which would list me the entires updated in the last 24h.

SELECT *
FROM your_table
WHERE last_updated >= NOW() - INTERVAL '24 HOURS';

Here's the rust code I tried:

use std::time::Duration;

use spacetimedb::{view, AnonymousViewContext, ViewContext, TimeDuration, Query};
use super::tables::{YourTable, your_table__view};
use crate::features::location::tables::your_table__query;


const DURATION_1H: u64 = 3_600;
const DURATION_24H: u64 = 24 * DURATION_1H;

/// Public view of the recently records in your_table.
///
/// Clients can subscribe directly to this view to receive updates on shared your_table entries.
#[view(accessor = recently_changed, public)]
pub fn recently_updated(ctx: &ViewContext) -> impl Query<YourTable> {
    const duration24h: TimeDuration = TimeDuration::from(Duration::from_secs(DURATION_24H));
    let last24h: u64 = ctx.timestamp - duration24h;
    ctx.from.your_table().r#where(|row| row.updated_at.gte(last24h))
}

However, ctx.timestamp is not defined. This is only available in a reducer.
But I don't want to modify any values, I just want to apply a filter.

Is the field ctx.timestamp missing a bug, or is this intended?
If so, how would this be best written in spacetimedb instead?

[luckydonald]

Ideas for a workaround:

• create a separate table with now timestamp in it which is updated by scheduled reducer every second and join that in view
• have a reducer which does not edit anything (is that an antipattern?) but does a query and returns the rows (I'm not sure if reducers can be watched)
• have a scheduled reducer which copies a filtered table your_table to recently_changed table (same columns) every second.
• connect via postgres and run SELECT * FROM your_table WHERE last_updated >= NOW() - INTERVAL '24 HOURS'; directly

[joshua-spacetime]

@luckydonald we haven't given ViewContext access to the current timestamp like reducers because there are performance implications, particularly with updating the view in realtime.

create a separate table with now timestamp in it which is updated by scheduled reducer every second and join that in view

For right now, this is the correct workaround. Just keep in mind that the view will be updated/evaluated every time you write to the now table.