Golang Value.Field方法代码示例

/*
Perform either case-sensitive or case-insensitive field lookup.
*/
func (this *Field) Apply(context Context, first, second value.Value) (value.Value, error) {
	switch second.Type() {
	case value.STRING:
		s := second.Actual().(string)
		v, ok := first.Field(s)

		if !ok && this.caseInsensitive {
			s = strings.ToLower(s)
			fields := first.Fields()
			for f, val := range fields {
				if s == strings.ToLower(f) {
					return value.NewValue(val), nil
				}
			}
		}

		return v, nil
	case value.MISSING:
		return value.MISSING_VALUE, nil
	default:
		if first.Type() == value.MISSING {
			return value.MISSING_VALUE, nil
		} else {
			return value.NULL_VALUE, nil
		}
	}
}

/*
This method takes in an object, a name and a value
and returns a new object that contains the name /
attribute pair. If the type of input is missing
then return a missing value, and if not an object
return a null value.
If the key is found, an error is thrown
*/
func (this *ObjectAdd) Apply(context Context, first, second, third value.Value) (value.Value, error) {

	// First must be an object, or we're out
	if first.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if first.Type() != value.OBJECT {
		return value.NULL_VALUE, nil
	}

	// second must be a non empty string
	if second.Type() != value.STRING || second.Actual().(string) == "" {
		return first, nil
	}

	field := second.Actual().(string)

	// we don't overwrite
	_, exists := first.Field(field)
	if exists {
		return value.NULL_VALUE, nil
	}

	// SetField will remove if the attribute is missing, but we don't
	// overwrite anyway, so we might just skip now
	if third.Type() != value.MISSING {
		rv := first.CopyForUpdate()
		rv.SetField(field, third)
		return rv, nil
	}
	return first, nil
}

/*
Compute the Final. Compute the sum and the count. If these
arent numbers throw an error. Compute the avg as sum/count.
Check for divide by zero, and return a NULL value if true.
*/
func (this *Avg) ComputeFinal(cumulative value.Value, context Context) (value.Value, error) {
	if cumulative == value.NULL_VALUE {
		return cumulative, nil
	}

	sum, _ := cumulative.Field("sum")
	count, _ := cumulative.Field("count")

	if sum.Type() != value.NUMBER || count.Type() != value.NUMBER {
		return nil, fmt.Errorf("Missing or invalid sum or count in AVG: %v, %v.",
			sum.Actual(), count.Actual())
	}

	if count.Actual().(float64) > 0.0 {
		return value.NewValue(sum.Actual().(float64) / count.Actual().(float64)), nil
	} else {
		return value.NULL_VALUE, nil
	}
}

func doGetPrepared(prepared_stmt value.Value, track bool) (*Prepared, errors.Error) {
	switch prepared_stmt.Type() {
	case value.STRING:
		prepared := cache.get(prepared_stmt, track)
		if prepared == nil {
			return nil, errors.NewNoSuchPreparedError(prepared_stmt.Actual().(string))
		}
		return prepared, nil
	case value.OBJECT:
		name_value, has_name := prepared_stmt.Field("name")
		if has_name {
			if prepared := cache.get(name_value, track); prepared != nil {
				return prepared, nil
			}
		}
		prepared_bytes, err := prepared_stmt.MarshalJSON()
		if err != nil {
			return nil, errors.NewUnrecognizedPreparedError(err)
		}
		return unmarshalPrepared(prepared_bytes)
	default:
		return nil, errors.NewUnrecognizedPreparedError(fmt.Errorf("Invalid prepared stmt %v", prepared_stmt))
	}
}

/*
Aggregate input partial values into cumulative result number value
for sum and count. If the partial results are not numbers, then
return an error.
*/
func (this *Avg) 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
	}

	psum, _ := part.Field("sum")
	pcount, _ := part.Field("count")
	csum, _ := cumulative.Field("sum")
	ccount, _ := cumulative.Field("count")

	if psum.Type() != value.NUMBER || pcount.Type() != value.NUMBER ||
		csum.Type() != value.NUMBER || ccount.Type() != value.NUMBER {
		return nil, fmt.Errorf("Missing or invalid partial sum or count in AVG: %v, %v, %v, v.",
			psum.Actual(), pcount.Actual(), csum.Actual(), ccount.Actual())
	}

	cumulative.SetField("sum", psum.Actual().(float64)+csum.Actual().(float64))
	cumulative.SetField("count", pcount.Actual().(float64)+ccount.Actual().(float64))
	return cumulative, nil
}

/*
Evaluate this as a top-level identifier.
*/
func (this *Identifier) Evaluate(item value.Value, context Context) (value.Value, error) {
	rv, _ := item.Field(this.identifier)
	return rv, nil
}