从OData v4开始增加了对单例模式的支持，我们不用每次根据主键等来获取某个EDM，就像在C#中使用单例模式一样。实现方式大致需要两步：
1、在需要实现单例模式的导航属性上加上[Singleton]特性
2、在EDM配置的时候使用builder.Singleton<SomeModel>("SomeModels")来创建SingletonConfiguration<SomeModel>
首先还是从模型开始。
public class Employee{ public int ID { get; set; } public string Name { get; set; } [Singleton] public Company Company { get; set; }}public enum CompanyCategory{ IT = 0, Communication = 1, Electronics = 2, Others = 3}public class Company{ public int ID { get; set; } public string Name { get; set; } public Int64 Revenue { get; set; } public CompanyCategory Category { get; set; } public List<Employee> Employees { get; set; }}
以上，Company和Employee存在1对多关系，我们在Employee的Compnay导航属性上加上了[Singleton]特性，也就意味着我们希望在Company上使用单例模式。
然后就在WebApiConfig中配置如下：
public static class WebApiConfig{ public static void Register(HttpConfiguration config) { ... config.MapODataServiceRoute("ODataRoute", "odata", GetEdmModel()); } public static IEdmModel GetEdmModel() { ODataConventionModelBuilder builder = new ODataConventionModelBuilder(); EntitySetConfiguration<Employee> employeesConfiguration = builder.EntitySet<Employee>("Employees"); EntityTypeConfiguration<Employee> employeeTypeConfiguration = employeesConfiguration.EntityType; employeeTypeConfiguration.Action("ResetDataSource"); SingletonConfiguration<Company> companiesConfiguration = builder.Singleton<Company>("Umbrella"); companiesConfiguration.EntityType.Action("ResetDataSource"); companiesConfiguration.EntityType.Function("GetEmployeesCount").Returns<int>(); builder.Namespace = "Hello"; return builder.GetEdmModel(); }}
以上，builder.Singleton<Company>("Umbrella")方法创建SingletonConfiguration<Company>类型的实例，这是EDM实现单例的方式。
Company对应的控制器UmbrellaController
再来看Company对应的控制器，大致如下:
public class UmbrellaController : ODataController{ public static Company Umbrella; static UmbrellaController() { InitData(); } private static void InitData() { Umbrella = new Company() { ID = 1, Name = "Umbrella", Revenue = 1000, Category = CompanyCategory.Communication, Employees = new List<Employee>() }; } ... [HttpPost] public IHttpActionResult ResetDataSourceOnCompany() { InitData(); return StatusCode(HttpStatusCode.NoContent); } public IHttpActionResult GetEmployeesCount() { return Ok(Umbrella.Employees.Count); }}
以上，UmbrellaController提供的静态Company类型的Umbrella可以在全局获取。ResetDataSourceOnCompany对应配置单例EDM的companiesConfiguration.EntityType.Action("ResetDataSource")的Action，GetEmployeesCount对应配置单例EDM的companiesConfiguration.EntityType.Function("GetEmployeesCount").Returns<int>()的Function。
● 查询
[EnableQuery]public IHttpActionResult Get(){ return Ok(Umbrella);}public IHttpActionResult GetRevenueFromCompany(){ return Ok(Umbrella.Revenue);}public IHttpActionResult GetName(){ return Ok(Umbrella.Employees);}
以上，GetRevenueFromCompany和GetName分别获取属性，要符合惯例，即"Get+属性名称"。
● 添加
public IHttpActionResult Put(Company newCompany){ Umbrella = newCompany; return StatusCode(HttpStatusCode.NoContent);}
● Patch
public IHttpActionResult Patch(Delta<Company> item){ item.Patch(Umbrella); return StatusCode(HttpStatusCode.NoContent);}
● 创建Company上的Employees关系
/// <summary>/// 创建Company上Employees的关系/// </summary>/// <param name="navigationProperty"></param>/// <param name="link">Empolyee的uri地址</param>/// <returns></returns>[AcceptVerbs("POST")]public IHttpActionResult CreateRef(string navigationProperty, [FromBody] Uri link){ //获取Employee的外键 int employeeId = HelperFunction.GetKeyValue<int>(link); Employee employee = EmployeesController.Employees.First(x => x.ID == employeeId); if(employee == null || navigationProperty!="Employees") { return BadRequest(); } if(Umbrella.Employees == null) { Umbrella.Employees = new List<Employee>() { employee}; } else { Umbrella.Employees.Add(employee); } return StatusCode(HttpStatusCode.NoContent);}
其实就是往Company的Employees集合导航属性中添加一个元素。其中，HelperFunction.GetKeyValue<int>()方法用来获取link中Empoyee的主键。如下：
public static class HelperFunction{ //获取主键值 public static TKey GetKeyValue<TKey>(Uri uri) { if(uri ==null) { throw new ArgumentException("uri"); } var rootPath = uri.AbsoluteUri.Substring(0, uri.AbsoluteUri.LastIndexOf('/') + 1); var odataUriParser = new ODataUriParser(WebApiConfig.GetEdmModel(), new Uri(rootPath), uri); var odataPath = odataUriParser.ParsePath(); var keySegment = odataPath.LastSegment as KeySegment; if(keySegment==null) { throw new InvalidOperationException("The link does not contain a key"); } return (TKey)keySegment.Keys.First().Value; }}
● 删除Company上的Employees关系
/// <summary>/// 删除关系/// </summary>/// <param name="relatedKey">Employee的主键</param>/// <param name="navigationProperty"></param>/// <returns></returns>public IHttpActionResult DeleteRef(string relatedKey, string navigationProperty){ int key = int.Parse(relatedKey); Employee employee = Umbrella.Employees.First(x => x.ID == key); if(navigationProperty != "Employees") { return BadRequest(); } Umbrella.Employees.Remove(employee); return StatusCode(HttpStatusCode.NoContent);}
其实就是删除Company的集合属性Employees中的一个Employee元素。
● 往Company的Employees集合里添加一个Employee元素
/// <summary>/// 从Compnay处添加某个Employee/// </summary>/// <param name="employee"></param>/// <returns></returns>[HttpPost]public IHttpActionResult PostToEmployees([FromBody] Employee employee){ EmployeesController.Employees.Add(employee); if(Umbrella.Employees == null) { Umbrella.Employees = new List<Employee>() { employee }; } else { Umbrella.Employees.Add(employee); } return Created(employee);}
EmployeesController不详诉
public class EmployeesController : ODataController{ public static List<Employee> Employees; static EmployeesController() { InitData(); } private static void InitData() { Employees = Enumerable.Range(0, 10).Select(i => new Employee() { ID = i, Name = string.Format("Name {0}", i) }).ToList(); } [EnableQuery] public IHttpActionResult Get() { return Ok(Employees.AsQueryable()); } [EnableQuery] public IHttpActionResult Get(int key) { return Ok(Employees.Where(e => e.ID == key)); } public IHttpActionResult GetCompanyFromEmployee([FromODataUri] int key) { var company = Employees.First(e => e.ID == key).Company; if(company==null) { return StatusCode(HttpStatusCode.NotFound); } return Ok(company); } public IHttpActionResult Post([FromBody] Employee employee) { Employees.Add(employee); return Created(employee); } [AcceptVerbs("PUT")] public IHttpActionResult CreateRef([FromODataUri] int key, string navigationProperty, [FromBody] Uri link) { if(navigationProperty!="Company") { return BadRequest(); } Employees.First(e => e.ID == key).Company = UmbrellaController.Umbrella; return StatusCode(HttpStatusCode.NoContent); } public IHttpActionResult DeleteRef([FromODataUri] int key, string navigationProperty) { if(navigationProperty!="Company") { return BadRequest(); } Employees.First(e => e.ID == key).Company = null; return StatusCode(HttpStatusCode.NoContent); } public IHttpActionResult PutToCompany(int key, Company company) { var navigateCompany = Employees.First(e => e.ID == key).Company; Employees.First(e => e.ID == key).Company = company; if(navigateCompany.Name == "Umbrella") { //体现Singleton UmbrellaController.Umbrella = navigateCompany; } else { return BadRequest(); } return StatusCode(HttpStatusCode.NoContent); } public IHttpActionResult PatchToCompany(int key, Delta<Company> company) { var navigateCompan = Employees.First(e => e.ID == key).Company; company.Patch(Employees.First(e => e.ID == key).Company); if(navigateCompan.Name == "Umbrella") { company.Patch(UmbrellaController.Umbrella); } else { return BadRequest(); } return StatusCode(HttpStatusCode.NoContent); } [HttpPost] public IHttpActionResult ResetDataSourceOnCollectionOfEmployee() { InitData(); return Ok(); }}
原标题：在ASP.NET Web API中使用OData的单例模式
关键词：ASP.NET
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