How can I create a generic UniqueValidationAttribute in C# and DataAnnotation?

Question

I\'m trying to create a UniqueAttribute using the System.ComponentModel.DataAnnotations.ValidationAttribute

I want this to be generic as in I c

Answer 1

I edited this one..and it works perfectly with DI..:D

public class UniqueAttribute : ValidationAttribute
{
    public UniqueAttribute(Type dataContextType, Type entityType, string propertyName)
    {
        DataContextType = dataContextType;
        EntityType = entityType;
        PropertyName = propertyName;
    }


    public Type DataContextType { get; private set; }


    public Type EntityType { get; private set; }


    public string PropertyName { get; private set; }


    public override bool IsValid(object value)
    {
        // Construct the data context
        //ConstructorInfo constructor = DataContextType.GetConstructor(new Type[0]);
        //DataContext dataContext = (DataContext)constructor.Invoke(new object[0]);
        var repository = DependencyResolver.Current.GetService(DataContextType);
        var data = repository.GetType().InvokeMember("GetAll", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.Public, null, repository, null);

        // Get the table
        //ITable table = dataContext.GetTable(EntityType);


        // Get the property
        PropertyInfo propertyInfo = EntityType.GetProperty(PropertyName);


        // Our ultimate goal is an expression of:
        //   "entity => entity.PropertyName == value"


        // Expression: "value"
        object convertedValue = Convert.ChangeType(value, propertyInfo.PropertyType);
        var rhs = Expression.Constant(convertedValue);


        // Expression: "entity"
        var parameter = Expression.Parameter(EntityType, "entity");


        // Expression: "entity.PropertyName"
        var property = Expression.MakeMemberAccess(parameter, propertyInfo);


        // Expression: "entity.PropertyName == value"
        var equal = Expression.Equal(property, rhs);


        // Expression: "entity => entity.PropertyName == value"
        var lambda = Expression.Lambda(equal, parameter).Compile();

        // Instantiate the count method with the right TSource (our entity type)
        MethodInfo countMethod = QueryableCountMethod.MakeGenericMethod(EntityType);

        // Execute Count() and say "you're valid if you have none matching"
        int count = (int)countMethod.Invoke(null, new object[] { data, lambda });
        return count == 0;
    }


    // Gets Queryable.Count(IQueryable, Expression>)
    //private static MethodInfo QueryableCountMethod = typeof(Enumerable).GetMethods().First(m => m.Name == "Count" && m.GetParameters().Length == 2);
    private static MethodInfo QueryableCountMethod = typeof(System.Linq.Enumerable).GetMethods().Single(
        method => method.Name == "Count" && method.IsStatic && method.GetParameters().Length == 2);
}