c# - 未定义 MemberExpression 属性

Question

我需要帮助。我有两个类:实体和模型。他们的代码如下。

public class TestEntityForSerialize
{
    public String FIO { get; set; }
    public DateTime Birthday { get; set; }
    public String Name { get; set; }
}

[DataContract]
public class TestModelForSerialize
{
    [DataMember]
    public String FIO { get; set; }
    [DataMember]
    public DateTime Birthday { get; set; }
    [DataMember(Name = "Name")]
    public String BigName { get; set; }
    public Int32 Age { get; set; }
}

主要任务是以编程方式转换任何Func<TestModelForSerialize, Boolean>至 Func <TestEntityForSerialize, Boolean> .我的决定是使用表达式树。我正在使用 ExpressionVisitor 迭代模型的表达式树的节点，并构建一个以实体作为参数的新表达式。这些 Func 的通用参数在类中设置，具有功能。

我已经通过覆盖 VisitParameter 方法成功地转换了 ParameterExpression，但我一直坚持覆盖 ExpressionVisitor 的后代的 VisitMember 方法。事实上我有代码:VisitMember 覆盖:

    protected override Expression VisitMember(MemberExpression node)
    {            
        Expression e = base.VisitMember(node);
        MemberExpression me = e as MemberExpression;
        if (me != null)
        {
            String modelPropertyName = ((PropertyInfo)me.Member).Name;
            ParameterExpression pe = node.Expression as ParameterExpression;
            TModel m = Activator.CreateInstance<TModel>();
            PropertyInfo memberPI = GetEntityProperty(m, modelPropertyName);
            MemberExpression meToReturn = Expression.Property(Expression.Parameter(typeof(TEntity)), memberPI);

            return meToReturn;
        }
        else
        {
            return base.VisitMember(node);
        }
    }

访问参数覆盖:

    protected override Expression VisitParameter(ParameterExpression node)
    {
        ParameterExpression pe = base.VisitParameter(node) as ParameterExpression;
        if (pe.Type == typeof(TModel))
        {
            ParameterExpression ex = Expression.Parameter(typeof(TEntity), pe.Name);
            return ex;
        }
        else
        {
            return pe;
        }
    }

GetEntityProperty 是将TModel 类的属性映射到TEntity 类的属性的方法。它使用DataContract和DataMember进行映射。

    protected PropertyInfo GetEntityProperty(TModel model, String propertyName)
    {
        PropertyInfo property = model.GetType().GetProperty(propertyName);
        if (property != null)
        {
            Attribute attr = property.GetCustomAttribute(typeof(DataMemberAttribute));
            if (attr != null)
            {
                String entityPropertyName = (((DataMemberAttribute)attr).Name != null ? ((DataMemberAttribute)attr).Name : propertyName);
                return typeof(TEntity).GetProperty(entityPropertyName);
            }
            else
            {
                throw new DataMemberAttributeNotFoundException();
            }
        }
        else
        {
            throw new MissingMemberException();
        }
    }

测试方法是

    [TestMethod]
    public void TestVisitMemberShouldReplaceModelWithEntity()
    {
        ParameterExpression p = Expression.Parameter(typeof(TestModelForSerialize));
        Type tm = typeof(TestModelForSerialize);
        PropertyInfo birthdayProp = tm.GetProperty("FIO");
        Assert.IsNotNull(birthdayProp);
        MemberExpression me = Expression.Property(p, birthdayProp);
        VisitorForTests vft = new VisitorForTests();
        MemberExpression meResult = vft.VisitMemberForTest(me) as MemberExpression;
        Assert.IsInstanceOfType(meResult.Member, typeof(PropertyInfo));
    }

VisitorForTests 是在类中调用 protected 方法的类，我正在尝试处理。方法:

    public Expression VisitMemberForTest(MemberExpression node)
    {
        return this.VisitMember(node);
    }

当我尝试调用 VisitMember 方法时，它在第一行(“Expression e = base.VisitMember(node);”)中崩溃，抛出带有消息的 ArgumentException:属性“FIO”未在类“TestEntityForSerialize”中定义.我唯一能注意到的是 - VisitMember 尝试启动 VisitParameter 方法，并在获得结果后崩溃。

非常感谢任何帮助。

Answer 1

明白了!正如俄罗斯谚语所说的那样，“拯救正在沉没的人——是这个人自己的事。”。问题是——我试图使用带有错误参数的表达式。它应该与 TEntity 的属性一起提供，而我会为它提供 TModel 的属性。所以只需稍微更改 VisitMember 方法和 Qawabanga!

    protected override Expression VisitMember(MemberExpression node)
    {            
        //Expression e = base.VisitMember(node); - I've commented this line
        MemberExpression me = node as MemberExpression;
        if (me != null)
        {
            String modelPropertyName = ((PropertyInfo)me.Member).Name;
            ParameterExpression pe = node.Expression as ParameterExpression;
            TModel m = Activator.CreateInstance<TModel>();
            PropertyInfo memberPI = GetEntityProperty(m, modelPropertyName);
            MemberExpression meToReturn = Expression.Property(Expression.Parameter(typeof(TEntity)), memberPI.Name);

            return base.VisitMember(meToReturn); //and changed this line
        }
        else
        {
            return base.VisitMember(node);
        }
    }

这有效!