动态生成具有嵌套属性的linq选择(select)

最新推荐文章于 2019-08-27 12:54:17 发布

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最新推荐文章于 2019-08-27 12:54:17 发布

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原文链接：http://www.cnblogs.com/myesn/p/10267915.html

本文介绍了一种使用C#表达式树将SelectList对象转换为SelectListDto对象的方法。通过反射获取源对象属性，并创建表达式树来绑定目标对象属性，实现类型之间的映射。

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    class SelectItem
    {
        public string Item { get; set; }
    }
    class SelectList
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public SelectItem Item { get; set; }
    }
    class SelectListDto : SelectList
    {

    }


        static Func<SelectList, SelectListDto> Test()
        {
            var entityType = typeof(SelectList);
            var selectListDtoType = typeof(SelectListDto);
            var selectItemType = typeof(SelectItem);
            var entityIDProperty = entityType.GetProperty("ID");
            var entityNameProperty = entityType.GetProperty("Name");
            var entityItemProperty = entityType.GetProperty("Item");
            var entityItemItemProperty = entityItemProperty.PropertyType.GetProperty("Item");
            var selectListDtoIDProperty = selectListDtoType.GetProperty("ID");
            var selectListDtoNameProperty = selectListDtoType.GetProperty("Name");
            var selectListDtoItemProperty = selectListDtoType.GetProperty("Item");
            var selectListDtoItemItemProperty = selectListDtoItemProperty.PropertyType.GetProperty("Item");

            var parameterExpression = Expression.Parameter(entityType);
            var newInstantiationExpression = Expression.New(selectListDtoType);

            var idMemberExpression = Expression.Property(parameterExpression, entityIDProperty);
            var nameMemberExpression = Expression.Property(parameterExpression, entityNameProperty);
            var itemMemberExpression = Expression.Property(parameterExpression, entityItemProperty);

            var innerObjNew = Expression.New(selectItemType);

            var nestedItemMemberExpression = Expression.Property(itemMemberExpression, entityItemItemProperty);

            var idBinding = Expression.Bind(selectListDtoIDProperty, idMemberExpression);
            var nameBinding = Expression.Bind(selectListDtoNameProperty, nameMemberExpression);
            var nestedItemBinding = Expression.Bind(entityItemItemProperty, nestedItemMemberExpression);

            var nestedInit = Expression.MemberInit(innerObjNew, nestedItemBinding);

            var nestedBinding = Expression.Bind(entityItemProperty, nestedInit);
            var bindings = new List<MemberAssignment>() { idBinding, nameBinding, nestedBinding};

            var memberInitExpression = Expression.MemberInit(newInstantiationExpression, bindings);

            var lambda = Expression.Lambda<Func<SelectList, SelectListDto>>(memberInitExpression, parameterExpression);
            return lambda.Compile();
        }

参考地址：

https://stackoverflow.com/a/51764873

https://stackoverflow.com/a/31465017/7712266

https://docs.microsoft.com/zh-cn/dotnet/csharp/expression-trees

转载于:https://www.cnblogs.com/myesn/p/10267915.html