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MaxLengthAttribute.cs
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MaxLengthAttribute.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
namespace System.ComponentModel.DataAnnotations
{
/// <summary>
/// Specifies the maximum length of collection/string data allowed in a property.
/// </summary>
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter,
AllowMultiple = false)]
public class MaxLengthAttribute : ValidationAttribute
{
private const int MaxAllowableLength = -1;
/// <summary>
/// Initializes a new instance of the <see cref="MaxLengthAttribute" /> class.
/// </summary>
/// <param name="length">
/// The maximum allowable length of collection/string data.
/// Value must be greater than zero.
/// </param>
public MaxLengthAttribute(int length)
: base(() => DefaultErrorMessageString)
{
Length = length;
}
/// <summary>
/// Initializes a new instance of the <see cref="MaxLengthAttribute" /> class.
/// The maximum allowable length supported by the database will be used.
/// </summary>
public MaxLengthAttribute()
: base(() => DefaultErrorMessageString)
{
Length = MaxAllowableLength;
}
/// <summary>
/// Gets the maximum allowable length of the collection/string data.
/// </summary>
public int Length { get; private set; }
private static string DefaultErrorMessageString
{
get { return SR.MaxLengthAttribute_ValidationError; }
}
/// <summary>
/// Determines whether a specified object is valid. (Overrides <see cref="ValidationAttribute.IsValid(object)" />)
/// </summary>
/// <remarks>
/// This method returns <c>true</c> if the <paramref name="value" /> is null.
/// It is assumed the <see cref="RequiredAttribute" /> is used if the value may not be null.
/// </remarks>
/// <param name="value">The object to validate.</param>
/// <returns>
/// <c>true</c> if the value is null or less than or equal to the specified maximum length, otherwise <c>false</c>
/// </returns>
/// <exception cref="InvalidOperationException">Length is zero or less than negative one.</exception>
public override bool IsValid(object value)
{
// Check the lengths for legality
EnsureLegalLengths();
var length = 0;
// Automatically pass if value is null. RequiredAttribute should be used to assert a value is not null.
if (value == null)
{
return true;
}
if (value is string str)
{
length = str.Length;
}
else if (value is ICollection collection)
{
length = collection.Count;
}
else
{
Type genericCol = value.GetType().GetInterfaces().FirstOrDefault(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(ICollection<>));
if (genericCol != null)
{
length = (int)genericCol.GetProperty("Count").GetValue(value);
}
else
{
throw new InvalidCastException(SR.Format(SR.LengthAttribute_InvalidValueType, value.GetType()));
}
}
return MaxAllowableLength == Length || length <= Length;
}
/// <summary>
/// Applies formatting to a specified error message. (Overrides <see cref="ValidationAttribute.FormatErrorMessage" />)
/// </summary>
/// <param name="name">The name to include in the formatted string.</param>
/// <returns>A localized string to describe the maximum acceptable length.</returns>
public override string FormatErrorMessage(string name)
{
// An error occurred, so we know the value is greater than the maximum if it was specified
return string.Format(CultureInfo.CurrentCulture, ErrorMessageString, name, Length);
}
/// <summary>
/// Checks that Length has a legal value.
/// </summary>
/// <exception cref="InvalidOperationException">Length is zero or less than negative one.</exception>
private void EnsureLegalLengths()
{
if (Length == 0 || Length < -1)
{
throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
SR.MaxLengthAttribute_InvalidMaxLength));
}
}
}
}