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Date math expressions

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Date math expressions

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The date type supports using date math expression when using it in a query/filter Whenever durations need to be specified, eg for a timeout parameter, the duration can be specified

The expression starts with an "anchor" date, which can be either now or a date string (in the applicable format) ending with ||. It can then follow by a math expression, supporting +, - and / (rounding). The units supported are

y (year)
M (month)
w (week)
d (day)
h (hour)
m (minute)
s (second)

as a whole number representing time in milliseconds, or as a time value like 2d for 2 days.

Be sure to read the Elasticsearch documentation on Date Math.

Simple expressions

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You can create simple expressions using any of the static methods on DateMath

Expect("now").WhenSerializing(Nest.DateMath.Now);
Expect("2015-05-05T00:00:00").WhenSerializing(Nest.DateMath.Anchored(new DateTime(2015,05, 05)));

strings implicitly convert to DateMath

Expect("now").WhenSerializing<Nest.DateMath>("now");

but are lenient to bad math expressions

var nonsense = "now||*asdaqwe";

the resulting date math will assume the whole string is the anchor

Expect(nonsense).WhenSerializing<Nest.DateMath>(nonsense)
    .Result(dateMath => ((IDateMath)dateMath)
        .Anchor.Match(
            d => d.Should().NotBe(default(DateTime)),
            s => s.Should().Be(nonsense)
        )
    );

DateTime also implicitly convert to simple date math expressions; the resulting anchor will be an actual DateTime, even after a serialization/deserialization round trip

var date = new DateTime(2015, 05, 05);
Expect("2015-05-05T00:00:00").WhenSerializing<Nest.DateMath>(date)
    .Result(dateMath => ((IDateMath)dateMath)
        .Anchor.Match(
            d => d.Should().Be(date),
            s => s.Should().BeNull()
        )
    );

Complex expressions

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Ranges can be chained on to simple expressions

Expect("now+1d").WhenSerializing(
    Nest.DateMath.Now.Add("1d"));

Including multiple operations

Expect("now+1d-1m").WhenSerializing(
    Nest.DateMath.Now.Add("1d").Subtract(TimeSpan.FromMinutes(1)));

A rounding value can be chained to the end of the expression, after which no more ranges can be appended

Expect("now+1d-1m/d").WhenSerializing(
    Nest.DateMath.Now.Add("1d")
        .Subtract(TimeSpan.FromMinutes(1))
        .RoundTo(Nest.TimeUnit.Day));

When anchoring dates, a || needs to be appended as clear separator between the anchor and ranges. Again, multiple ranges can be chained

Expect("2015-05-05T00:00:00||+1d-1m").WhenSerializing(
    Nest.DateMath.Anchored(new DateTime(2015,05,05))
        .Add("1d")
        .Subtract(TimeSpan.FromMinutes(1)));

Fractional times

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DateMath expressions do not support fractional numbers so unlike Time DateMath will pick the biggest integer unit it can represent

Expect("now+25h").WhenSerializing(
    Nest.DateMath.Now.Add(TimeSpan.FromHours(25)));

where as Time on its own serializes like this

Expect("1.04166666666667d").WhenSerializing(new Time(TimeSpan.FromHours(25)));

Expect("now+90001s").WhenSerializing(
    Nest.DateMath.Now.Add(TimeSpan.FromHours(25).Add(TimeSpan.FromSeconds(1))));

Expect("now+90000001ms").WhenSerializing(
    Nest.DateMath.Now.Add(TimeSpan.FromHours(25).Add(TimeSpan.FromMilliseconds(1))));

Expect("now+1y").WhenSerializing(
    Nest.DateMath.Now.Add("1y"));

Expect("now+52w").WhenSerializing(
    Nest.DateMath.Now.Add(TimeSpan.FromDays(7 * 52)));

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