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DistinctValuesAttribute.cs
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/
DistinctValuesAttribute.cs
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using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
namespace Qowaiv.ComponentModel.DataAnnotations
{
/// <summary>Specifies that all values are distinct.</summary>
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]
public sealed class DistinctValuesAttribute : ValidationAttribute
{
/// <summary>Creates a new instance of <see cref="DistinctValuesAttribute"/>.</summary>
/// <remarks>
/// The type of the custom <see cref="IEqualityComparer"/> or <see cref="IEqualityComparer{T}"/> (for <see cref="object"/>).
/// </remarks>
public DistinctValuesAttribute(Type comparer = null)
: base(() => QowaivComponentModelMessages.DistinctValuesAttribute_ValidationError)
{
EqualityComparer = CreateComparer(comparer);
}
/// <summary>Gets and set a custom <see cref="IEqualityComparer"/>.</summary>
public IEqualityComparer<object> EqualityComparer { get; }
/// <summary>True if all items in the collection are distinct, otherwise false.</summary>
public override bool IsValid(object value)
{
if (value is null)
{
return true;
}
var collection = Guard.IsInstanceOf<IEnumerable>(value, nameof(value)).Cast<object>();
var checker = new HashSet<object>(EqualityComparer);
return collection.All(checker.Add);
}
/// <summary>Creates the Comparer to do the distinct with.</summary>
private static IEqualityComparer<object> CreateComparer(Type comparer)
{
if (comparer is null)
{
return EqualityComparer<object>.Default;
}
if(typeof(IEqualityComparer<object>).IsAssignableFrom(comparer))
{
return (IEqualityComparer<object>)Activator.CreateInstance(comparer);
}
if (typeof(IEqualityComparer).IsAssignableFrom(comparer))
{
return new WrappedComparer((IEqualityComparer)Activator.CreateInstance(comparer));
}
throw new ArgumentException(string.Format(QowaivComponentModelMessages.ArgumentException_TypeIsNotEqualityComparer, comparer), nameof(comparer));
}
/// <summary>As there is no none generic hash set.</summary>
private class WrappedComparer : IEqualityComparer<object>
{
private readonly IEqualityComparer _comparer;
public WrappedComparer(IEqualityComparer comparer) => _comparer = comparer;
public new bool Equals(object x, object y) => _comparer.Equals(x, y);
public int GetHashCode(object obj) => _comparer.GetHashCode(obj);
}
}
}