上一篇写的是使用静态基类方法的实现步骤: http://www.cnblogs.com/cgzl/p/8726805.html
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<TSource>(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<string, object>)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<string, object>)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<LinkViewModel> CreateLinksForCustomer(int id, string fields = null) { var links = new List<LinkViewModel>(); 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<IActionResult> Get(int id, string fields) { var item = await _customerRepository.GetSingleAsync(id); if (item == null) { return NotFound(); } var customerVm = Mapper.Map<CustomerViewModel>(item); var links = CreateLinksForCustomer(id, fields); var dynamicObject = customerVm.ToDynamic(fields) as IDictionary<string, object>; dynamicObject.Add("links", links); return Ok(dynamicObject); } [HttpPost(Name = "CreateCustomer")] public async Task<IActionResult> Post([FromBody] CustomerViewModel customerVm) { if (customerVm == null) { return BadRequest(); } if (!ModelState.IsValid) { return BadRequest(ModelState); } var newItem = Mapper.Map<Customer>(customerVm); _customerRepository.Add(newItem); if (!await UnitOfWork.SaveAsync()) { return StatusCode(500, "保存时出错"); } var vm = Mapper.Map<CustomerViewModel>(newItem); var links = CreateLinksForCustomer(vm.Id); var dynamicObject = vm.ToDynamic() as IDictionary<string, object>; 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<LinkViewModel> CreateLinksForCustomers(string fields = null) { var links = new List<LinkViewModel>(); 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<ExpandoObject> ToDynamicIEnumerable<TSource>(this IEnumerable<TSource> source, string fields) { if (source == null) { throw new ArgumentNullException("source"); } var expandoObjectList = new List<ExpandoObject>(); var propertyInfoList = new List<PropertyInfo>(); 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<string, object>)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<IActionResult> GetAll(string fields) { var items = await _customerRepository.GetAllAsync(); var results = Mapper.Map<IEnumerable<CustomerViewModel>>(items); var dynamicList = results.ToDynamicIEnumerable(fields); var links = CreateLinksForCustomers(fields); var dynamicListWithLinks = dynamicList.Select(customer => { var customerDictionary = customer as IDictionary<string, object>; 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:
