Golang Value.Collate方法代码示例

/*
This method evaluates the less than equal to condition and
returns a value representing if the two operands satisfy the
condition or not. If either of the input operands are
missing, return missing value, and if they are null, then
return null value. For all other types call the Collate
method and check if it is less than equal to 0 for the
two values. If it is, then return true.
*/
func (this *LE) Apply(context Context, first, second value.Value) (value.Value, error) {
	if first.Type() == value.MISSING || second.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if first.Type() == value.NULL || second.Type() == value.NULL {
		return value.NULL_VALUE, nil
	}

	return value.NewValue(first.Collate(second) <= 0), nil
}

/*
This method evaluates the between comparison operation and returns a
value representing if item value is in between low and high. If any of
the input operands are missing, return missing, and if null return null.
For all other types, check if the item is greater in terms of the N1QL
collation order, than the low value and smaller than high value, and return
true. If not return false.
*/
func (this *Between) Apply(context Context, item, low, high value.Value) (value.Value, error) {
	if item.Type() == value.MISSING || low.Type() == value.MISSING || high.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if item.Type() == value.NULL || low.Type() == value.NULL || high.Type() == value.NULL {
		return value.NULL_VALUE, nil
	}

	return value.NewValue(item.Collate(low) >= 0 && item.Collate(high) <= 0), nil
}

/*
Aggregate input partial values into cumulative result value.
If partial result is null return the current cumulative value,
and if the cumulative result is null, return the partial value.
For non null partial and cumulative values, call Collate and
return the smaller value depending on the N1QL collation order.
*/
func (this *Min) cumulatePart(part, cumulative value.Value, context Context) (value.Value, error) {
	if part == value.NULL_VALUE {
		return cumulative, nil
	} else if cumulative == value.NULL_VALUE {
		return part, nil
	} else if part.Collate(cumulative) < 0 {
		return part, nil
	} else {
		return cumulative, nil
	}
}

func (this *Order) Less(i, j int) bool {
	v1 := this.values[i]
	v2 := this.values[j]

	var ev1, ev2 value.Value
	var c int
	var e error

	for i, term := range this.plan.Terms() {
		s := strconv.Itoa(i)

		sv1 := v1.GetAttachment(s)
		switch sv1 := sv1.(type) {
		case value.Value:
			ev1 = sv1
		default:
			ev1, e = term.Expression().Evaluate(v1, this.context)
			if e != nil {
				this.context.Error(errors.NewError(e, "Error evaluating ORDER BY."))
				return false
			}

			v1.SetAttachment(s, ev1)
		}

		sv2 := v2.GetAttachment(s)
		switch sv2 := sv2.(type) {
		case value.Value:
			ev2 = sv2
		default:
			ev2, e = term.Expression().Evaluate(v2, this.context)
			if e != nil {
				this.context.Error(errors.NewError(e, "Error evaluating ORDER BY."))
				return false
			}

			v2.SetAttachment(s, ev2)
		}

		c = ev1.Collate(ev2)

		if c == 0 {
			continue
		} else if term.Descending() {
			return c > 0
		} else {
			return c < 0
		}
	}

	return false
}