EF8多列唯一索引扩展方法的Linq表达式兼容问题及原理咨询

我在EF 8（.NET 8）中编写了一个扩展方法，用于更便捷地添加多列唯一索引。EF内置的EntityTypeBuilder<TEntityType>.HasIndex方法，基于字符串的重载使用不便，而支持表达式语法的重载仅允许创建单列索引，因此我实现了如下扩展方法：

public static IndexBuilder<TEntityType> HasIndexUnique<TEntityType>
(
    this EntityTypeBuilder<TEntityType> builder,
    string indexName,
    IEnumerable<Expression<Func<TEntityType, object?>>> includeExpressions
) where TEntityType : class
{
    if ((includeExpressions is null) || (!includeExpressions.Any()))
    {
        var currentMethod = MethodBase.GetCurrentMethod();
        throw (new Exception($@"The method [{currentMethod?.DeclaringType?.FullName}.{currentMethod?.Name}] was called without any [{nameof(includeExpressions)}]."));
    }

    var propertyNames = includeExpressions
        .Select
        (
            e =>
            // Casting issue depending on what was sent in.
            ((MemberExpression) ((UnaryExpression) e.Body).Operand).Member.Name
        )
        .ToArray();

    var indexBuilder = builder
        .HasIndex
        (
            propertyNames,
            $@"{indexName}"
        )
        .IsUnique(unique: true);

    return (indexBuilder);
}

当调用该方法传入Int64类型属性时，代码运行正常：

builder
    .HasIndexUnique
    (
        "Index_IndexName_Unique",
        e => e.ModelId,
        e => e.ModelEntityPrincipleId,
        e => e.ModelEntityDependentId,
        e => e.ModelEntityBridgeId
    );

但传入String类型属性时，表达式转换会抛出异常：

builder.HasIndexUnique("Index_IndexName_Unique", e => e.Name);

// 异常发生在这一行：
((MemberExpression) ((UnaryExpression) e.Body).Operand).Member.Name
System.InvalidCastException: 'Unable to cast object of type 'System.Linq.Expressions.PropertyExpression' to type 'System.Linq.Expressions.UnaryExpression'.'

我需要解决两个问题：

• 实现能检测并处理Int64、String、DateTime、Object、Byte[]类型属性的表达式转换逻辑，避免异常；
• 理解为什么Int64和String类型属性对应的表达式类型分别是UnaryExpression和PropertyExpression？

附实体类代码：

public partial class ModelEntityRelationship:
    IEntity<ModelEntityRelationship>
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }

    public virtual long ModelId { get; set; }
    public virtual Model Model { get; set; }

    public virtual long ModelEntityPrincipleId { get; set; }
    public virtual ModelEntity ModelEntityPrinciple { get; set; } = new();

    public virtual long ModelEntityDependentId { get; set; }
    public virtual ModelEntity ModelEntityDependent { get; set; } = new();

    public virtual long? ModelEntityBridgeId { get; set; }
    public virtual ModelEntity? ModelEntityBridge { get; set; }
}

内容的提问来源于stack exchange，提问作者Raheel Khan