Program.cs代码:

  class Program
    {
        private static void Main(string[] args)
        {
            var st = new Student { Id = 10, Name = "爱因斯坦" };
            ParameterExpression paraExpr = Expression.Parameter(st.GetType());
            //访问 st=>st.Name  
            PropertyInfo idProp = st.GetType().GetProperty("Id");
            BlockExpression idExpr = CreatePropertyAccesorExpression(idProp, paraExpr, null); //生成的表达式大意为："st.Id"  
            Expression<Func<Student, int>> idlambda = Expression.Lambda<Func<Student, int>>(idExpr, paraExpr);
            //生成的表达式大意为："st=>st.Id"  
            Func<Student, int> idFunc = idlambda.Compile(); //生成相应的delegate；  
            int idValue = idFunc(st); //执行： st=>st.Id;  
            Console.WriteLine("id= " + idValue); //输出  
            //现在访问 st=>st.Location.Row ; 由于Location为null，因此，我们期望访问的Row属性默认值为：0  
            PropertyInfo localProp = st.GetType().GetProperty("Location");
            BlockExpression localExpr = CreatePropertyAccesorExpression(localProp, paraExpr, null);
            //生成的表达式大意为："st.Location!=null?st.Location:null"  
            PropertyInfo rowProp = localProp.PropertyType.GetProperty("Row");
            /*生成的表达式大意为： 
             * var parentExpr = st.Location!=null?st.Location:null; 
             * if(parentExpr!=null){ 
             * return parentExpr.Row; 
             * }else{ 
             * return default(int); 
             * } 
             */
            BlockExpression rowExpr = CreatePropertyAccesorExpression(rowProp, localExpr, null);
            //生成lambda： st=>(rowExpr表达式块）  
            Expression<Func<Student, int>> rowlambda = Expression.Lambda<Func<Student, int>>(rowExpr, paraExpr);
            Func<Student, int> rowFunc = rowlambda.Compile(); //生成相应的delegate  
            int rowValue = rowFunc(st); //执行： st=>（rowExpr表达式块）  
            Console.WriteLine("rowValue= " + rowValue);

            Console.ReadKey();
        }


        private static BlockExpression CreatePropertyAccesorExpression(PropertyInfo prop, Expression parentExpr,
            object defaultValue)
        {
            //默认值  
            if (defaultValue == null && prop.PropertyType.IsValueType)
            {
                defaultValue = Activator.CreateInstance(prop.PropertyType);
            }
            //默认返回Expression  
            ConstantExpression defaultExpr = Expression.Constant(defaultValue, prop.PropertyType);
            //测试当前属性的“父属性”是否非空  
            BinaryExpression test = Expression.NotEqual(parentExpr, Expression.Constant(null));
            //“父属性”非空时的返回值  
            MemberExpression propExpr = Expression.Property(parentExpr, prop);
            LabelTarget labelTarget = Expression.Label(prop.PropertyType);
            //局部变量，用于存放最终的返回值  
            ParameterExpression locExpr = Expression.Variable(prop.PropertyType);
            //测试并赋值  
            ConditionalExpression ifesleTestExpr = Expression.IfThenElse(test, Expression.Assign(locExpr, propExpr),
                Expression.Assign(locExpr, defaultExpr));
            //返回值  
            GotoExpression retExpr = Expression.Return(labelTarget, locExpr);
            LabelExpression labelExpr = Expression.Label(labelTarget, locExpr);
            BlockExpression block = Expression.Block(
                new[] { locExpr },
                ifesleTestExpr,
                retExpr,
                labelExpr
                );
            return block;
        }
    }

运行结果如图: