Class DateTimeSubtractTime

Namespace

YndigoBlue.Velocity.Functions

Assembly

YndigoBlue.Velocity.dll

Represents a function that subtracts a Time-of-day value from a DateTime as a duration from midnight, returning a new DateTime.

public class DateTimeSubtractTime : Function, ICheckItem, IDefaultItem, IFilterItem, IElement

Inheritance

object

Function

DateTimeSubtractTime

Implements

ICheckItem

IDefaultItem

IFilterItem

IElement

Remarks

DateTimeSubtractTime(datetime, time) → datetime shifted back by the time duration.

The time argument is treated as a duration rather than an absolute clock time: a value of 02:30:00 subtracts two hours and thirty minutes from the datetime regardless of its existing time component.

Both arguments may be column references or literal values. To add a time duration instead, use DateTimeAddTime.

Examples

Recover the original datetime by subtracting a time offset column from an adjusted datetime:

var schema = manager.LoadSchema("scheduling");
var appointments = schema["appointments"];

var query = new Query()
    .Select([ appointments["id"], new Expression("base_datetime", new DateTimeSubtractTime(appointments["adjusted_at"], appointments["offset_time"])) ])
    .From(appointments);

var results = manager.Retrieve(query);

Use the column + TimeOnly constructor to subtract a fixed time-of-day offset from each datetime:

var schema = manager.LoadSchema("scheduling");
var appointments = schema["appointments"];
Column adjustedAtColumn = appointments["adjusted_at"];

// Remove the 08:30 offset that was added to all appointment datetimes
var startTime = new TimeOnly(8, 30, 0);

var query = new Query()
    .Select([ appointments["id"], new Expression("original_at", new DateTimeSubtractTime(adjustedAtColumn, startTime)) ])
    .From(appointments);

var results = manager.Retrieve(query);

Use the DateTime + TimeOnly constructor to subtract a fixed time duration from a literal datetime:

var adjustedDate = new DateTime(2024, 6, 1, 14, 0, 0);
var shift = new TimeOnly(14, 0, 0);   // 14:00 = 14 hours

// Returns 2024-06-01 00:00:00
var expr = new DateTimeSubtractTime(adjustedDate, shift);

Constructors

DateTimeSubtractTime(DateTime, TimeOnly)

Initializes a new instance of DateTimeSubtractTime with a DateTime literal and a TimeOnly literal.

DateTimeSubtractTime(DateTime, Column)

Initializes a new instance of DateTimeSubtractTime with a DateTime literal and a time column.

DateTimeSubtractTime(IElement, IElement)

Initializes a new instance of DateTimeSubtractTime.

DateTimeSubtractTime(Column, TimeOnly)

Initializes a new instance of DateTimeSubtractTime with a DateTime column and a TimeOnly literal.

DateTimeSubtractTime(Column, Column)

Initializes a new instance of DateTimeSubtractTime with both arguments as columns.