Tencent/WeKnora · error

in operator value must be a slice with at least one value: %

Error message

in operator value must be a slice with at least one value: %v

What it means

convertInCondition requires the IN/NOT_IN Value to be a slice containing at least one element. It uses reflection to check Value's kind and length and returns this error when Value is not a slice or is an empty slice, including Value's content in the message.

Source

Thrown at internal/application/repository/retriever/milvus/filter.go:171

	case operatorBetween:
		return c.convertBetweenCondition(cond, counter)
	default:
		return nil, fmt.Errorf("unsupported operator: %v", cond.Operator)
	}
}

func (c *filter) convertInCondition(
	cond *universalFilterCondition,
	counter *int,
) (*convertResult, error) {
	condField := cond.Field
	if condField == "" || cond.Value == nil {
		return nil, fmt.Errorf("milvus filter condition is nil")
	}

	s := reflect.ValueOf(cond.Value)
	if s.Kind() != reflect.Slice || s.Len() <= 0 {
		return nil, fmt.Errorf("in operator value must be a slice with at least one value: %v", cond.Value)
	}

	paramName := c.convertParamName(cond.Field, counter)
	return &convertResult{
		exprStr: fmt.Sprintf("%s %s {%s}", condField, strings.ToLower(cond.Operator), paramName),
		params:  map[string]any{paramName: cond.Value},
	}, nil
}

func (c *filter) convertBetweenCondition(
	cond *universalFilterCondition,
	counter *int,
) (*convertResult, error) {
	condField := cond.Field
	if condField == "" || cond.Value == nil {
		return nil, fmt.Errorf("milvus filter condition is nil")
	}

View on GitHub (pinned to 988cbb0330)

Solutions

1. Ensure Value is a non-empty slice (e.g. []string{...} or []int{...})
2. If a single value is intended, use the EQUAL operator instead of IN
3. Guard the length before building the condition

Example fix

// before
cond := &UniversalFilterCondition{Field: "tag", Operator: "IN", Value: "red"}
// after
cond := &UniversalFilterCondition{Field: "tag", Operator: "IN", Value: []string{"red"}}

rv := reflect.ValueOf(cond.Value)
if rv.Kind() != reflect.Slice || rv.Len() == 0 {
  return fmt.Errorf("IN requires a non-empty slice")
}

func isInSlice(c *UniversalFilterCondition) bool {
  if c.Value == nil { return false }
  v := reflect.ValueOf(c.Value)
  return v.Kind() == reflect.Slice && v.Len() > 0
}

res, err := f.Convert(ctx, cond)
if err != nil {
  if strings.Contains(err.Error(), "must be a slice") {
    return nil, fmt.Errorf("IN value must be a non-empty slice: %w", err)
  }
  return nil, err
}

When it happens

Trigger: IN condition with Value as a scalar (e.g. a single string), a map, or an empty slice like []string{}.

Common situations: Passing a single value intending 'equals'; JSON arrays that ended up empty after filtering; Go interface{} wrapping that loses the slice type.

Related errors

• between operator value must be a slice with two elements: %v
• milvus filter condition is nil
• unsupported comparison operator: %s
• invalid logical condition value type
• empty logical condition

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/5077d99815d615cb. Report an issue: GitHub.