Troubleshooting

This page lists problems that come up in practice, with their causes. Build errors and warnings with an id of the form VM#### are covered in the diagnostics reference.

The registration method does not exist

services.AddShopValidators() does not compile:

• The project does not reference ValidationModules.SourceGenerator. The generator package does not flow from a referenced project, so every project that declares validated types needs it.
• The name is different. It comes from the assembly name, so check AssemblyName in the project file. Registration gives the rules.
• The project declares no validated types, so there is nothing to register.
• The generator is referenced as a project rather than a package. A ProjectReference to the generator needs OutputItemType="Analyzer" and ReferenceOutputAssembly="false".

No service for IValidatorFor<T>

• The registration method for the assembly that declares T was not called. Each project has its own method.
• T has no rules, so no validator was generated. Add constraints, a rules class, or [GenerateValidator].
• ValidationModules_DataAnnotations is set to Ignore, and T has only DataAnnotations attributes, so no validator was generated for it.

Error CS7036 on Validate

new SignUpValidator().Validate(signUp) fails with error CS7036, which says no argument was given for the parameter value of SignUpValidator.Validate(ref ValidationContext, SignUp). The file does not import the ValidationModules namespace. Validate(value) is an extension method in that namespace. Without it, the compiler finds only the validator's own Validate method, which takes a context. Add using ValidationModules;.

A rule is not checked

• The value is null. Every constraint except [Required] passes null.
• The attribute is on a field or a static property. The generator reads instance properties only, and reports VM1011.
• The attribute is on an indexer. The generator reports VM1014.
• The attribute is on a positional record parameter without the property: target. The generator reports VM1008.
• A derived class hides the property with new, which replaces the base property's constraints. The generator reports VM1009.
• The nested object has no [ValidateNested], or the nested type has no rules (VM1501), or it is declared in another assembly and this project can reach no validator for it (VM1505).
• A When or Unless condition excluded it.
• The generator reported an error or warning for the constraint and dropped it. Check the build output for VM diagnostics.

Error CS1729 or CS1739 on [StringLength]

[StringLength(3, 40)] fails with error CS1729, and [StringLength(min: 3)] with error CS1739. [StringLength] reads its arguments as the DataAnnotations attribute of the same name does: the one positional argument is the maximum, and the minimum is the named Min. Write [StringLength(40, Min = 3)] or [StringLength(Min = 3)].

Earlier versions took the minimum first. A one-argument [StringLength(50)] written against them meant at least 50 characters, and it now means at most 50, so search for that form when upgrading.

[Pattern] accepts values it should not

[Pattern] passes when the expression matches anywhere in the value. Anchor it with ^ and $ to match the whole value.

Every error appears twice

The validators are registered twice. Either the registration method is called twice, or a DependencyModules application calls it as well as adding the module that already registers the validators. Call it once.

A hand-written validator does not run

• The code resolves a single IValidatorFor<T>, which returns only the last validator registered. Resolve ValidationRunner<T> instead.
• The validator was created with new. A validator created that way does not use the container, so it never runs hand-written validators for nested types.
• It is an IAsyncValidatorFor<T>, and the code calls Validate rather than ValidateAsync, or an earlier error stopped the async stage. See Async validation.

Cannot resolve scoped service ValidationRunner

ValidationRunner<T> is registered as scoped. Resolve it from a scope created with provider.CreateScope(), or inject it into a scoped service or a request handler.

The validation pass carries no services

An InvalidOperationException that says the validation pass carries no services comes from a descent with Polymorphism.Runtime, on [ValidateNested] or on Nested or Each in a rules class. The validators for the value's actual type are looked up in the container during validation, and validator.Validate(value) has no container. Validate through ValidationRunner<T> resolved from a scope, or pass the provider to a ValidationErrorCollector.

No IValidatorFor is registered, compose the validators from another assembly

A rules class that calls rules.As<TFacet>(x) with an interface from another assembly throws an InvalidOperationException that names that assembly and its registration method. It has two causes. Either that registration method was not called, or the pass has no service provider, as with validator.Validate(value), even though the method was called. Call the method, and validate through ValidationRunner<T> resolved from a scope.

Validation nested more than 64 levels deep

The object being validated contains a cycle, such as an object that is its own child, or it is nested more than 64 levels deep. The limit cannot be raised.

An endpoint fails on the first request

.Validate<T>() checks its setup when the endpoints are built, which happens on the first request. It throws when the handler has no parameter of type T, or when no validator is registered for T. Endpoints are built together, so every endpoint fails. See ASP.NET Core.

Messages are always in English

ValidationError.Message always returns the default English text. Format the error with error.ToMessage(formatter), where the formatter is the ValidationMessageFormatter registered for your language packs. Also check that CultureInfo.CurrentUICulture is set, and that the application does not use invariant globalization. See Messages and languages.

Field names do not match the JSON

Field names are camelCase by default and ignore the application's JSON options. Put [JsonPropertyName] on the property, or set ValidationModules_FieldNaming. See Field names.

A language pack has no effect

• The file name must end in .validation-messages.json.

• CultureInfo.CurrentUICulture must be the pack's culture or one of its child cultures, and the application must not use invariant globalization.

• The message must come through a formatter, with error.ToMessage(formatter), or through the ASP.NET Core problem details response. error.Message stays in English.

• Authored messages are not replaced. See Authored messages.

• The generator is referenced as a project rather than a package, so the package's build targets that pick up pack files are not imported. List the files yourself:

  <ItemGroup>
    <AdditionalFiles Include="Messages/*.validation-messages.json" />
  </ItemGroup>

An MSBuild property has no effect

• The value is not one the property accepts. The generator then uses the default and reports VM5004, which lists the values the property accepts. Case does not matter.

• The generator is referenced as a project rather than a package. The package's build targets declare which properties the generator can read, and a ProjectReference does not import them. Declare the property yourself:

  <ItemGroup>
    <CompilerVisibleProperty Include="ValidationModules_FieldNaming" />
  </ItemGroup>

A breakpoint in Describe never hits

The generator reads Describe and never calls it. Set the breakpoint in the generated code. See How it works.

Error CS0104: ambiguous reference

Required, Range and several other attribute names exist in both ValidationModules.Constraints and System.ComponentModel.DataAnnotations, and ValidationResult and ValidationContext exist in both ValidationModules and System.ComponentModel.DataAnnotations. Import one of each pair per file, or alias one. See DataAnnotations.