MudBlazor/MudBlazor · error · ArgumentOutOfRangeException

Unknown operator name.

Error message

Unknown operator name.

What it means

FilterOperator.GetOperatorName maps each filter-operator enum value to a localized display string via a switch. Several arms are commented out (Boolean.Is, DateTime.Is/IsNot/Empty/NotEmpty, Guid.Equal/NotEqual), so passing any of those operator values reaches the default arm and throws ArgumentOutOfRangeException. It also fires for any out-of-range operator value.

Source

Thrown at src/MudBlazor/Components/DataGrid/FilterOperator.cs:384

            Number.GreaterThanOrEqual => LanguageResource.MudDataGrid_GreaterThanOrEqualSign,
            Number.LessThan => LanguageResource.MudDataGrid_LessThanSign,
            Number.LessThanOrEqual => LanguageResource.MudDataGrid_LessThanOrEqualSign,
            //Number.Empty => LanguageResource.MudDataGrid_IsEmpty,
            //Number.NotEmpty => LanguageResource.MudDataGrid_IsNotEmpty,
            Enum.Is => LanguageResource.MudDataGrid_Is,
            Enum.IsNot => LanguageResource.MudDataGrid_IsNot,
            //Boolean.Is => LanguageResource.MudDataGrid_Is,
            //DateTime.Is => LanguageResource.MudDataGrid_Is,
            //DateTime.IsNot => LanguageResource.MudDataGrid_IsNot,
            DateTime.After => LanguageResource.MudDataGrid_IsAfter,
            DateTime.OnOrAfter => LanguageResource.MudDataGrid_IsOnOrAfter,
            DateTime.Before => LanguageResource.MudDataGrid_IsBefore,
            DateTime.OnOrBefore => LanguageResource.MudDataGrid_IsOnOrBefore,
            //DateTime.Empty => LanguageResource.MudDataGrid_IsEmpty,
            //DateTime.NotEmpty => LanguageResource.MudDataGrid_IsNotEmpty,
            //Guid.Equal => LanguageResource.MudDataGrid_Equals,
            //Guid.NotEqual => LanguageResource.MudDataGrid_NotEquals,
            _ => throw new ArgumentOutOfRangeException(nameof(operatorName), operatorName, "Unknown operator name.")
        };
    }
}

View on GitHub (pinned to bdb3acd5dd)

Solutions

1. Only surface operators that FilterOperator.GetOperatorByDataType returns for the column's data type.
2. Avoid requesting GetOperatorName for commented-out operator values.
3. If you must reference Guid/Boolean/DateTime equality, use the operators that remain active (e.g. Guid.Equal may be unsupported — use a supported alternative or filter manually).

Example fix

// before
var name = FilterOperator.GetOperatorName(FilterOperator.DateTime.Empty);

// after
// use a supported DateTime operator, e.g.:
var name = FilterOperator.GetOperatorName(FilterOperator.DateTime.Before);

var allowed = FilterOperator.GetOperatorByDataType(propertyType);
if (!allowed.Contains(op))
{
    // skip or pick a supported operator
}

static bool IsOperatorSupported(FilterOperator op, Type type)
    => FilterOperator.GetOperatorByDataType(type).Contains(op);

try { name = FilterOperator.GetOperatorName(op); }
catch (ArgumentOutOfRangeException) { /* operator not localized; skip it */ }

When it happens

Trigger: Requesting the display name for an operator whose localization arm is commented out (e.g. FilterOperator.DateTime.Empty, FilterOperator.Guid.Equal); passing an undefined operator enum integer; the filter UI trying to render a label for a disabled operator.

Common situations: Custom filter templates that surface every operator including the disabled ones; upgrading MudBlazor where an operator was deprecated; constructing a FilterDefinition with an operator not yet localized.

Related errors

• Invalid filter operators for {PropertyType?.Name}: {string.J
• {GetType()} can only accept one item source from its paramet
• {GetType()} can only accept one item source from its paramet
• {GetType()} can only accept one item source from its paramet
• Do not supply both '{nameof(VirtualizeServerData)}' and '{na

AI-assisted analysis of MudBlazor/MudBlazor@bdb3acd5dd (2026-08-13). Data as JSON: /api/errors/780ad6d7c0433fe4. Report an issue: GitHub.