表达式树深度> 1的成员访问(Expression tree for a member acc

public class Job
{
    public string Name { get; set; }
    public int Salary { get; set; }
}
public class Employee
{
    public string Name { get; set; }
    public Job Job { get; set; }
}

如果我想创建一个成员访问到Employee.Name的表达式目录树，这是我做的：

        var param = Expression.Parameter(type, "x");
        var memberAccess = Expression.PropertyOrField(param, memberName);
        return Expression.Lambda<Func<TModel, TMember>>(memberAccess, param);

什么是相当于这一个成员访问Employee.Job.Salary？

Answer 1:

你需要：

var jobProperty = Expression.PropertyOrField(param, "Job");
var salaryProperty = Expression.PropertyOrField(jobProperty, "Salary");

基本上你正在做的Salary从评估的结果性质x.Job 。

如果你需要做这以编程的方式，你需要这样的：

Expression expression = Expression.Parameter(type, "x");
foreach (var property in properties.Split('.'))
{
    expression = Expression.PropertyOrField(expression, property);
}

Answer 2:

将创建扩展的最好方法如下 ：

public static class ExpressionExtensions
{
    /// <summary>
    ///     create expression by property name
    /// </summary>
    /// <typeparam name="TModel"></typeparam>
    /// <param name="propertyName">
    ///     <example>Urer.Role.Name</example>
    /// </param>
    /// <returns></returns>
    public static Expression<Func<TModel, dynamic>> CreateExpression<TModel>(this string propertyName) {
        Type currentType = typeof (TModel);
        ParameterExpression parameter = Expression.Parameter(currentType, "x");
        Expression expression = parameter;

        int i = 0;
        List<string> propertyChain = propertyName.Split('.').ToList();
        do {
            System.Reflection.PropertyInfo propertyInfo = currentType.GetProperty(propertyChain[i]);
            currentType = propertyInfo.PropertyType;
            i++;
            if (propertyChain.Count == i)
            {
                currentType = typeof (object);
            }
            expression = Expression.Convert(Expression.PropertyOrField(expression, propertyInfo.Name), currentType);
        } while (propertyChain.Count > i);

        return Expression.Lambda<Func<TModel, dynamic>>(expression, parameter);
    }
}

您不能转换（）来的typeof（对象），每次，因为System.Object的没有财产，那你的类型有（如姓名或薪水在你的例子）。

文章来源: Expression tree for a member access of depth > 1