上一篇写的是使用静态基类方法的实现步骤:

使用dynamic (ExpandoObject)的好处就是可以动态组建返回类型, 之前使用的是ViewModel, 如果想返回结果的话, 肯定需要把ViewModel所有的属性都返回, 如果属性比较多, 就有可能造成性能和灵活性等问题. 而使用ExpandoObject(dynamic)就可以解决这个问题.

返回一个对象

返回一个dynamic类型的对象, 需要把所需要的属性从ViewModel抽取出来并转化成dynamic对象, 这里所需要的属性通常是从参数传进来的, 例如针对下面的CustomerViewModel类, 参数可能是这样的: "Name, Company":

using System;using SalesApi.Core.Abstractions.DomainModels;namespace SalesApi.ViewModels{    public class CustomerViewModel: EntityBase    {        public string Company { get; set; }        public string Name { get; set; }        public DateTimeOffset EstablishmentTime { get; set; }    }}

还需要一个Extension Method可以把对象按照需要的属性转化成dynamic类型:

using System;using System.Collections.Generic;using System.Dynamic;using System.Reflection;namespace SalesApi.Shared.Helpers{    public static class ObjectExtensions    {        public static ExpandoObject ToDynamic
     
      (this TSource source, string fields = null)        {            if (source == null)            {                throw new ArgumentNullException("source");            }            var dataShapedObject = new ExpandoObject();            if (string.IsNullOrWhiteSpace(fields))            {                // 所有的 public properties 应该包含在ExpandoObject里                 var propertyInfos = typeof(TSource).GetProperties(BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);                foreach (var propertyInfo in propertyInfos)                {                    // 取得源对象上该property的值                    var propertyValue = propertyInfo.GetValue(source);                    // 为ExpandoObject添加field                    ((IDictionary
      
       )dataShapedObject).Add(propertyInfo.Name, propertyValue);                }                return dataShapedObject;            }            // field是使用 "," 分割的, 这里是进行分割动作.            var fieldsAfterSplit = fields.Split(',');            foreach (var field in fieldsAfterSplit)            {                var propertyName = field.Trim();                // 使用反射来获取源对象上的property                // 需要包括public和实例属性， 并忽略大小写.                var propertyInfo = typeof(TSource).GetProperty(propertyName, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);                if (propertyInfo == null)                {                    throw new Exception($"没有在‘{typeof(TSource)}’上找到‘{propertyName}’这个Property");                }                // 取得源对象property的值                var propertyValue = propertyInfo.GetValue(source);                // 为ExpandoObject添加field                ((IDictionary
       
        )dataShapedObject).Add(propertyInfo.Name, propertyValue);            }            return dataShapedObject;        }    }}

注意: 这里的逻辑是如果没有选择需要的属性的话, 那么就返回所有合适的属性.

然后在CustomerController里面:

首先创建为对象添加link的方法:

private IEnumerable
     
       CreateLinksForCustomer(int id, string fields = null)        {            var links = new List
      
       ();            if (string.IsNullOrWhiteSpace(fields))            {                links.Add(                    new LinkViewModel(_urlHelper.Link("GetCustomer", new { id = id }),                    "self",                    "GET"));            }            else            {                links.Add(                    new LinkViewModel(_urlHelper.Link("GetCustomer", new { id = id, fields = fields }),                    "self",                    "GET"));            }            links.Add(                new LinkViewModel(_urlHelper.Link("DeleteCustomer", new { id = id }),                "delete_customer",                "DELETE"));            links.Add(                new LinkViewModel(_urlHelper.Link("CreateCustomer", new { id = id }),                "create_customer",                "POST"));            return links;        }

针对返回一个对象, 添加了本身的连接, 添加的连接以及删除的连接.

然后修改Get和Post的Action:

[HttpGet]        [Route("{id}", Name = "GetCustomer")]        public async Task
     
       Get(int id, string fields)        {            var item = await _customerRepository.GetSingleAsync(id);            if (item == null)            {                return NotFound();            }            var customerVm = Mapper.Map
      
       (item);            var links = CreateLinksForCustomer(id, fields);            var dynamicObject = customerVm.ToDynamic(fields) as IDictionary
       
        ;            dynamicObject.Add("links", links);            return Ok(dynamicObject);        }        [HttpPost(Name = "CreateCustomer")]        public async Task
        
          Post([FromBody] CustomerViewModel customerVm)        {            if (customerVm == null)            {                return BadRequest();            }            if (!ModelState.IsValid)            {                return BadRequest(ModelState);            }            var newItem = Mapper.Map
         
          (customerVm);            _customerRepository.Add(newItem);            if (!await UnitOfWork.SaveAsync())            {                return StatusCode(500, "保存时出错");            }            var vm = Mapper.Map
          
           (newItem); var links = CreateLinksForCustomer(vm.Id); var dynamicObject = vm.ToDynamic() as IDictionary
           
            ; dynamicObject.Add("links", links); return CreatedAtRoute("GetCustomer", new { id = dynamicObject["Id"] }, dynamicObject); }

红色部分是相关的代码. 创建links之后把vm对象按照需要的属性转化成dynamic对象. 然后往这个dynamic对象里面添加links属性. 最后返回该对象.

下面测试一下.

POST:

结果:

由于POST方法里面没有选择任何fields, 所以返回所有的属性.

下面试一下GET:

再试一下GET, 选择几个fields:

OK, 效果都如预期.

但是有一个问题, 因为返回的json的Pascal case的(只有dynamic对象返回的是Pascal case, 其他ViewModel现在返回的都是camel case的), 而camel case才是更好的选择 .

所以在Startup里面可以这样设置:

services.AddMvc(options =>            {                options.ReturnHttpNotAcceptable = true;                // the default formatter is the first one in the list.                options.OutputFormatters.Remove(new XmlDataContractSerializerOutputFormatter());                // set authorization on all controllers or routes                var policy = new AuthorizationPolicyBuilder()                    .RequireAuthenticatedUser()                    .Build();                options.Filters.Add(new AuthorizeFilter(policy));            })            .AddJsonOptions(options =>            {                options.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();            })            .AddFluetValidations();

然后再试试:

OK.

返回集合

首先编写创建links的方法:

private IEnumerable
     
       CreateLinksForCustomers(string fields = null)        {            var links = new List
      
       ();            if (string.IsNullOrWhiteSpace(fields))            {                links.Add(                   new LinkViewModel(_urlHelper.Link("GetAllCustomers", new { fields = fields }),                   "self",                   "GET"));            }            else            {                links.Add(                   new LinkViewModel(_urlHelper.Link("GetAllCustomers", new { }),                   "self",                   "GET"));            }            return links;        }

这个很简单.

然后需要针对IEnumerable<T>类型创建把ViewModel转化成dynamic对象的Extension方法:

using System;using System.Collections.Generic;using System.Dynamic;using System.Reflection;namespace SalesApi.Shared.Helpers{    public static class IEnumerableExtensions    {        public static IEnumerable
     
       ToDynamicIEnumerable
      
       (this IEnumerable
       
         source, string fields)        {            if (source == null)            {                throw new ArgumentNullException("source");            }            var expandoObjectList = new List
        
         ();            var propertyInfoList = new List
         
          ();            if (string.IsNullOrWhiteSpace(fields))            {                var propertyInfos = typeof(TSource).GetProperties(BindingFlags.Public | BindingFlags.Instance);                propertyInfoList.AddRange(propertyInfos);            }            else            {                var fieldsAfterSplit = fields.Split(',');                foreach (var field in fieldsAfterSplit)                {                    var propertyName = field.Trim();                    var propertyInfo = typeof(TSource).GetProperty(propertyName, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);                    if (propertyInfo == null)                    {                        throw new Exception($"Property {propertyName} wasn't found on {typeof(TSource)}");                    }                    propertyInfoList.Add(propertyInfo);                }            }            foreach (TSource sourceObject in source)            {                var dataShapedObject = new ExpandoObject();                foreach (var propertyInfo in propertyInfoList)                {                    var propertyValue = propertyInfo.GetValue(sourceObject);                    ((IDictionary
          
           )dataShapedObject).Add(propertyInfo.Name, propertyValue); } expandoObjectList.Add(dataShapedObject); } return expandoObjectList; } }}

注意: 反射的开销很大, 注意性能.

然后修改GetAll方法:

[HttpGet(Name = "GetAllCustomers")]        public async Task
     
       GetAll(string fields)        {            var items = await _customerRepository.GetAllAsync();            var results = Mapper.Map
      
       
        >(items);            var dynamicList = results.ToDynamicIEnumerable(fields);            var links = CreateLinksForCustomers(fields);            var dynamicListWithLinks = dynamicList.Select(customer =>            {                var customerDictionary = customer as IDictionary
        
         ;                var customerLinks = CreateLinksForCustomer(                    (int)customerDictionary["Id"], fields);                customerDictionary.Add("links", customerLinks);                return customerDictionary;            });            var resultWithLink = new {                Value = dynamicListWithLinks,                Links = links            };            return Ok(resultWithLink);        }

红色部分是相关代码.

测试一下:

不选择属性:

选择部分属性:

OK.

HATEOAS这部分就写到这.

其实翻页的逻辑很适合使用HATEOAS结构. 有空我再写一个翻页的吧.

下面是我的关于ASP.NET Core Web API相关技术的公众号--草根专栏: