FSharp.Validations

FSharp Validations is a validation library designed with a functional first approach.

The library supports:

• The ability to create rules for properties using the RuleFor<'a, 'b> function
• The ability to apply a list of rules to a propery using Rule<'a>
• the ability to reuse validators using ruleSetFor<'a, 'b>
• The creation of RuleSets<'a> -> 'a ValidationResult

The rules can then be evaluated at any time thanks to the magic of currying.

openFSharp.ValidationstypeFoo={ Bar:string }letvalidateFoo=
ruleSet [
ruleFor <@_.Bar @>[
rule (fun x -> x.Length >0)(Some "Length must be greater than 0")
rule (fun x -> x.Length <10)(Some "Length must be less than 10")]]letresult= validateFoo { Bar ="Hello, World!"}// result is Failure (map [("Bar", ["Value must be less than 10"])])

Reusing Rule Sets

Rule sets can be reused by creating a RuleSet<'a> and applying it to a property using the ruleSetFor<'a, 'b> function.

typeBar={ Value:string }typeFoo={ Bar:Bar }letvalidateBar=
ruleSet [
ruleFor <@_.Value @>[
rule (fun x -> x.Length >0)(Some "Length must be greater than 0")
rule (fun x -> x.Length <10)(Some "Length must be less than 10")]]letvalidateFoo=
ruleSet [
ruleSetFor <@_.Bar @> validateBar ]

Any resulting errors for Bar will have a key of Bar.{propertyName}.

ValidationResult<'a>

A Success represents the entity that has passed validations.

A Failure represents a Map<string, string list> where the key is the property that failed and value is a collection of all the messages attached to the failure upon validation.

letresult= validateFoo { bar ="Hello, World!"}match result with| Success value -> printfn "%A" value
| Failure errors -> errors |> Map.iter (printfn "%s: %A")

Dependency Injection

A function is provided to convert any 'a -> 'a ValidationResult to an 'a IValidator using the provided toValidator function.

The resulting 'a IValidator can be used for Dependency Injection.

openMicrosoft.Extensions.DependencyInjectiontypeFoo={ Bar:string }letvalidateFoo=
ruleSet<Foo>[ ruleFor <@_.Bar @>[ notEmpty ]]letfooValidator= validateFoo |> toValidator
letresult= fooValidator.Validate({ Bar ="Hello, World!"})// Add to Dependency Injectionletservices= ServiceCollection():> IServiceCollection
services.AddScoped<Foo IValidator>(fun _ -> fooValidator)|> ignore

License, Copywright, Etc.

FSharp.Validations is subject to copywright @ 2025 Oneirosoft and other contributors under the MIT License.