How to Compare Object Properties in C#?

A detailed explanation of C# object properties

In scenarios such as unit testing or data verification, the need to compare object property values ​​is very common. C# provides multiple methods to achieve this functionality, each with its own pros and cons.

Method 1: Use reflection

The reflection mechanism allows dynamic inspection of properties of objects and comparison of their values. Here is a reflection-based comparison method:

public bool PropertiesEqual(object comparisonObject)
{
    Type sourceType = this.GetType();
    Type destinationType = comparisonObject.GetType();

    if (sourceType == destinationType)
    {
        PropertyInfo[] sourceProperties = sourceType.GetProperties();
        foreach (PropertyInfo pi in sourceProperties)
        {
            if ((sourceType.GetProperty(pi.Name).GetValue(this, null) == null && destinationType.GetProperty(pi.Name).GetValue(comparisonObject, null) == null))
            {
                // 两个属性都为 null，无需比较
            }
            else if (!(sourceType.GetProperty(pi.Name).GetValue(this, null).ToString() == destinationType.GetProperty(pi.Name).GetValue(comparisonObject, null).ToString()))
            {
                // 只要一个属性值不同，则返回 false
                return false;
            }
        }
    }
    else
    {
        throw new ArgumentException("比较对象必须为同一类型。", "comparisonObject");
    }

    return true;
}

Method 2: Using generics and LINQ

Generics and LINQ provide a simpler comparison method:

public static bool PublicInstancePropertiesEqual<T>(T self, T to, params string[] ignore) where T : class
{
    if (self != null && to != null)
    {
        Type type = typeof(T);
        List<string> ignoreList = new List<string>(ignore);
        var unequalProperties =
            from pi in type.GetProperties(BindingFlags.Public | BindingFlags.Instance)
            where !ignoreList.Contains(pi.Name) && pi.GetUnderlyingType().IsSimpleType() && pi.GetIndexParameters().Length == 0
            let selfValue = type.GetProperty(pi.Name).GetValue(self, null)
            let toValue = type.GetProperty(pi.Name).GetValue(to, null)
            where selfValue != toValue && (selfValue == null || !selfValue.Equals(toValue))
            select selfValue;
        return !unequalProperties.Any();
    }
    return self == to;
}

public static class TypeExtensions
{
    public static bool IsSimpleType(this Type type)
    {
        return
            type.IsValueType ||
            type.IsPrimitive ||
            new[]
            {
                typeof(String),
                typeof(Decimal),
                typeof(DateTime),
                typeof(DateTimeOffset),
                typeof(TimeSpan),
                typeof(Guid)
            }.Contains(type) ||
            (Convert.GetTypeCode(type) != TypeCode.Object);
    }

    public static Type GetUnderlyingType(this MemberInfo member)
    {
        switch (member.MemberType)
        {
            case MemberTypes.Event:
                return ((EventInfo)member).EventHandlerType;
            case MemberTypes.Field:
                return ((FieldInfo)member).FieldType;
            case MemberTypes.Method:
                return ((MethodInfo)member).ReturnType;
            case MemberTypes.Property:
                return ((PropertyInfo)member).PropertyType;
            default:
                throw new ArgumentException("输入的 MemberInfo 必须是 EventInfo、FieldInfo、MethodInfo 或 PropertyInfo 类型");
        }
    }
}

Notes

• Performance: Reflection is less performant than directly accessing properties.
• Type safety: Generic methods ensure type safety and reduce errors.
• Extensibility: Extension methods facilitate integration into other code.
• Limitations: Both methods may not handle properties containing complex objects or circular references.

Summary

Method selection depends on specific needs. For scenarios with high performance requirements, it is recommended to access properties directly; for scenarios that require type safety and scalability, the generic LINQ method is more suitable.

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