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CompareValidator

The CompareValidator component validates user input by comparing it to a constant value or to the value of another control using a comparison operator (equals, greater than, less than, etc.). Original Web Forms documentation is at: https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.comparevalidator?view=netframework-4.8

Features Supported in Blazor

  • Comparison operators: Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual, DataTypeCheck
  • Data type validation: String, Integer, Double, Date, Currency
  • ValueToCompare property for comparing against a constant value
  • CultureInvariantValues for culture-independent comparisons
  • ErrorMessage display when validation fails
  • Integration with EditForm validation

Web Forms Features NOT Supported

  • ControlToCompare is not directly supported; use ValueToCompare with binding instead
  • Display property (Static, Dynamic, None) - Blazor handles rendering differently
  • SetFocusOnError - Blazor has different focus management

Syntax Comparison

=== "Web Forms"

```html
<asp:CompareValidator
    ControlToCompare="string"
    ControlToValidate="string"
    CultureInvariantValues="True|False"
    Display="None|Static|Dynamic"
    EnableClientScript="True|False"
    Enabled="True|False"
    ErrorMessage="string"
    ForeColor="color name|#dddddd"
    ID="string"
    Operator="Equal|NotEqual|GreaterThan|GreaterThanEqual|LessThan|
        LessThanEqual|DataTypeCheck"
    runat="server"
    SetFocusOnError="True|False"
    Text="string"
    Type="String|Integer|Double|Date|Currency"
    ValidationGroup="string"
    ValueToCompare="string"
    Visible="True|False"
/>
```

=== "Blazor"

```razor
<CompareValidator TValue="string"
    ValueToCompare="100"
    Operator="ValidationCompareOperator.GreaterThan"
    Type="ValidationDataType.Integer"
    ErrorMessage="Value must be greater than 100" />
```

Usage Notes

The CompareValidator is a generic component that takes a type parameter TValue. It inherits from BaseCompareValidator which provides the core comparison logic.

Example: Comparing to a Constant Value

<EditForm Model="@model">
    <InputNumber @bind-Value="model.Age" />
    <CompareValidator TValue="int"
        ValueToCompare="18"
        Operator="ValidationCompareOperator.GreaterThanEqual"
        Type="ValidationDataType.Integer"
        ErrorMessage="You must be at least 18 years old" />
</EditForm>

Supported Operators

Operator Description
Equal Values must be equal
NotEqual Values must not be equal
GreaterThan Input must be greater than comparison value
GreaterThanEqual Input must be greater than or equal to comparison value
LessThan Input must be less than comparison value
LessThanEqual Input must be less than or equal to comparison value
DataTypeCheck Validates that input can be converted to the specified data type

Supported Data Types

Type Description
String Text comparison
Integer Whole number comparison
Double Decimal number comparison
Date Date comparison
Currency Currency value comparison

Migration Notes

  1. Remove asp: prefix — Change <asp:CompareValidator> to <CompareValidator>
  2. Remove runat="server" — Not needed in Blazor
  3. Add generic type parameter — Use TValue="int" or TValue="string" etc.
  4. Operator uses enum — Change Operator="GreaterThan" to Operator="ValidationCompareOperator.GreaterThan"
  5. Type uses enum — Change Type="Integer" to Type="ValidationDataType.Integer"
  6. Remove EnableClientScript — Not applicable in Blazor
  7. Remove SetFocusOnError — Not supported in Blazor

Migration Example

=== "Web Forms"

```html
<asp:TextBox ID="txtAge" runat="server" />
<asp:CompareValidator
    ControlToValidate="txtAge"
    Operator="GreaterThanEqual"
    ValueToCompare="18"
    Type="Integer"
    ErrorMessage="Must be 18 or older"
    runat="server" />
```

=== "Blazor"

```razor
<InputNumber @bind-Value="model.Age" />
<CompareValidator TValue="int"
    ControlToValidate="Age"
    Operator="ValidationCompareOperator.GreaterThanEqual"
    ValueToCompare="18"
    Type="ValidationDataType.Integer"
    ErrorMessage="Must be 18 or older" />
```

See Also