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NDLRGEN016: Validation method not found

Cause

The ValidateMethod specified in [Options] does not exist on the target type.

Rule Description

When you use [Options(ValidateMethod = "MethodName")], the generator looks for a method with that name on: 1. The options class itself (if no Validator is specified) 2. The validator class (if Validator is specified)

If the method doesn't exist, this error is raised.

How to Fix

Add the method with the correct name:

// ❌ Wrong - method name doesn't match
[Options(ValidateMethod = "ValidateSettings", ValidateOnStart = true)]
public class AppSettings
{
    public string Name { get; set; } = "";

    // Method is named "Validate", not "ValidateSettings"
    public IEnumerable<ValidationError> Validate() { ... }
}

// ✅ Correct - method name matches
[Options(ValidateMethod = "ValidateSettings", ValidateOnStart = true)]
public class AppSettings
{
    public string Name { get; set; } = "";

    public IEnumerable<ValidationError> ValidateSettings()
    {
        if (string.IsNullOrEmpty(Name))
            yield return "Name is required";
    }
}

Example

Code with Error

using NexusLabs.Needlr.Generators;

// NDLRGEN016: Method 'CheckValidity' not found on type 'DatabaseOptions'
[Options(ValidateMethod = "CheckValidity", ValidateOnStart = true)]
public class DatabaseOptions
{
    public string ConnectionString { get; set; } = "";

    // No method named "CheckValidity" exists!
}

Fixed Code

using NexusLabs.Needlr.Generators;

[Options(ValidateMethod = "CheckValidity", ValidateOnStart = true)]
public class DatabaseOptions
{
    public string ConnectionString { get; set; } = "";

    // ✅ Added the method with matching name
    public IEnumerable<ValidationError> CheckValidity()
    {
        if (string.IsNullOrEmpty(ConnectionString))
            yield return "ConnectionString is required";
    }
}

Using Convention-Based Naming

If you name your method Validate, you don't need to specify ValidateMethod:

// No need for ValidateMethod - "Validate" is discovered by convention
[Options(ValidateOnStart = true)]
public class CacheOptions
{
    public int TimeoutSeconds { get; set; }

    // Convention: method named "Validate" is auto-discovered
    public IEnumerable<ValidationError> Validate()
    {
        if (TimeoutSeconds <= 0)
            yield return "TimeoutSeconds must be positive";
    }
}

See Also