在前面的文章中我们提到Entity Framework的“Code First”模式也同样可以基于现有数据库进行开发。今天就让我们一起看一下使用Entity Framework Power Tools如何基于现有数据库生成数据类和数据库上下等。
Entity Framework Power Tools
基于现有数据库生成POCO数据类和数据库上下文需要借助Visual Studio一个扩展插件-- Entity Framework Power Tools（一个Code First反向工程工具）。只要在Visual Studio扩展里面输入“Entity Framework Power”搜索即可找到最新的扩展，点击下载即可（如下图）。当然你也可以到这里下载安装包进行安装。
安装完之后只要在项目上右键选择Entity Framework->Reverse Engineer Code First（项目中首先需要安装Entity Framework 包，否则会有错误），然后在弹出的窗口中输入相关的数据库连接信息即可（我们这里使用“AdventureWorks”数据库）。
 | 注意：如果使用“AdventureWorks”数据库，可能发生如下错误： One or more errors occurred while loading schema information. error 6004: The table 'AdventureWorks.Production.Document' is referenced by a relationship, but cannot be found. 这是由于EF目前还不支持SQL Server 2008中新增的“”数据类型，目前只有先不用该类型的数据了，暂时将它改为其他类型。 |
然后我们稍等片刻，可以看到Entity Framework Power Tools已经根据所选数据库自动为你生成了数据类、数据库上下文操作类、对应的映射配置类并添加了数据库连接配置。
我们先看一下配置文件，可以看到在配置文件中Entity Framework Power Tools已经自动对数据库连接串进行了配置，添加了名为“AdventureWorksContext”的数据库连接串：
与此同时，对生成的数据库上下文操作类“AdventureWorksContext”进行了配置，在构造函数中使用了上面配置的“AdventureWorksContext”数据库连接：
using System.Data.Entity;using System.Data.Entity.Infrastructure;using EFPowerTools.Models.Mapping;namespace EFPowerTools.Models{ public partial class AdventureWorksContext : DbContext { static AdventureWorksContext() { Database.SetInitializer (null); } public AdventureWorksContext() : base("Name=AdventureWorksContext") { } public DbSet AWBuildVersions { get; set; } public DbSet DatabaseLogs { get; set; } public DbSet ErrorLogs { get; set; } public DbSet OrderDetails { get; set; } public DbSet Orders { get; set; } public DbSet Departments { get; set; } public DbSet Employees { get; set; } public DbSet EmployeeDepartmentHistories { get; set; } public DbSet EmployeePayHistories { get; set; } public DbSet JobCandidates { get; set; } public DbSet Shifts { get; set; } public DbSet Addresses { get; set; } public DbSet AddressTypes { get; set; } public DbSet BusinessEntities { get; set; } public DbSet BusinessEntityAddresses { get; set; } public DbSet BusinessEntityContacts { get; set; } public DbSet ContactTypes { get; set; } public DbSet CountryRegions { get; set; } public DbSet EmailAddresses { get; set; } public DbSet Passwords { get; set; } public DbSet People { get; set; } public DbSet PersonPhones { get; set; } public DbSet PhoneNumberTypes { get; set; } public DbSet StateProvinces { get; set; } public DbSet BillOfMaterials { get; set; } public DbSet Cultures { get; set; } public DbSet Illustrations { get; set; } public DbSet Locations { get; set; } public DbSet Products { get; set; } public DbSet ProductCategories { get; set; } public DbSet ProductCostHistories { get; set; } public DbSet ProductDescriptions { get; set; } public DbSet ProductInventories { get; set; } public DbSet ProductListPriceHistories { get; set; } public DbSet ProductModels { get; set; } public DbSet ProductModelIllustrations { get; set; } public DbSet ProductModelProductDescriptionCultures { get; set; } public DbSet ProductPhotoes { get; set; } public DbSet ProductProductPhotoes { get; set; } public DbSet ProductReviews { get; set; } public DbSet ProductSubcategories { get; set; } public DbSet ScrapReasons { get; set; } public DbSet TransactionHistories { get; set; } public DbSet TransactionHistoryArchives { get; set; } public DbSet UnitMeasures { get; set; } public DbSet WorkOrders { get; set; } public DbSet WorkOrderRoutings { get; set; } public DbSet ProductVendors { get; set; } public DbSet PurchaseOrderDetails { get; set; } public DbSet PurchaseOrderHeaders { get; set; } public DbSet ShipMethods { get; set; } public DbSet Vendors { get; set; } public DbSet CountryRegionCurrencies { get; set; } public DbSet CreditCards { get; set; } public DbSet Currencies { get; set; } public DbSet CurrencyRates { get; set; } public DbSet Customers { get; set; } public DbSet PersonCreditCards { get; set; } public DbSet SalesOrderDetails { get; set; } public DbSet SalesOrderHeaders { get; set; } public DbSet SalesOrderHeaderSalesReasons { get; set; } public DbSet SalesPersons { get; set; } public DbSet SalesPersonQuotaHistories { get; set; } public DbSet SalesReasons { get; set; } public DbSet SalesTaxRates { get; set; } public DbSet SalesTerritories { get; set; } public DbSet SalesTerritoryHistories { get; set; } public DbSet ShoppingCartItems { get; set; } public DbSet SpecialOffers { get; set; } public DbSet SpecialOfferProducts { get; set; } public DbSet Stores { get; set; } public DbSet vEmployees { get; set; } public DbSet vEmployeeDepartments { get; set; } public DbSet vEmployeeDepartmentHistories { get; set; } public DbSet vJobCandidates { get; set; } public DbSet vJobCandidateEducations { get; set; } public DbSet vJobCandidateEmployments { get; set; } public DbSet vAdditionalContactInfoes { get; set; } public DbSet vStateProvinceCountryRegions { get; set; } public DbSet vProductAndDescriptions { get; set; } public DbSet vProductModelCatalogDescriptions { get; set; } public DbSet vProductModelInstructions { get; set; } public DbSet vVendorWithAddresses { get; set; } public DbSet vVendorWithContacts { get; set; } public DbSet vIndividualCustomers { get; set; } public DbSet vPersonDemographics { get; set; } public DbSet vSalesPersons { get; set; } public DbSet vSalesPersonSalesByFiscalYears { get; set; } public DbSet vStoreWithAddresses { get; set; } public DbSet vStoreWithContacts { get; set; } public DbSet vStoreWithDemographics { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Configurations.Add(new AWBuildVersionMap()); modelBuilder.Configurations.Add(new DatabaseLogMap()); modelBuilder.Configurations.Add(new ErrorLogMap()); modelBuilder.Configurations.Add(new OrderDetailMap()); modelBuilder.Configurations.Add(new OrderMap()); modelBuilder.Configurations.Add(new DepartmentMap()); modelBuilder.Configurations.Add(new EmployeeMap()); modelBuilder.Configurations.Add(new EmployeeDepartmentHistoryMap()); modelBuilder.Configurations.Add(new EmployeePayHistoryMap()); modelBuilder.Configurations.Add(new JobCandidateMap()); modelBuilder.Configurations.Add(new ShiftMap()); modelBuilder.Configurations.Add(new AddressMap()); modelBuilder.Configurations.Add(new AddressTypeMap()); modelBuilder.Configurations.Add(new BusinessEntityMap()); modelBuilder.Configurations.Add(new BusinessEntityAddressMap()); modelBuilder.Configurations.Add(new BusinessEntityContactMap()); modelBuilder.Configurations.Add(new ContactTypeMap()); modelBuilder.Configurations.Add(new CountryRegionMap()); modelBuilder.Configurations.Add(new EmailAddressMap()); modelBuilder.Configurations.Add(new PasswordMap()); modelBuilder.Configurations.Add(new PersonMap()); modelBuilder.Configurations.Add(new PersonPhoneMap()); modelBuilder.Configurations.Add(new PhoneNumberTypeMap()); modelBuilder.Configurations.Add(new StateProvinceMap()); modelBuilder.Configurations.Add(new BillOfMaterialMap()); modelBuilder.Configurations.Add(new CultureMap()); modelBuilder.Configurations.Add(new IllustrationMap()); modelBuilder.Configurations.Add(new LocationMap()); modelBuilder.Configurations.Add(new ProductMap()); modelBuilder.Configurations.Add(new ProductCategoryMap()); modelBuilder.Configurations.Add(new ProductCostHistoryMap()); modelBuilder.Configurations.Add(new ProductDescriptionMap()); modelBuilder.Configurations.Add(new ProductInventoryMap()); modelBuilder.Configurations.Add(new ProductListPriceHistoryMap()); modelBuilder.Configurations.Add(new ProductModelMap()); modelBuilder.Configurations.Add(new ProductModelIllustrationMap()); modelBuilder.Configurations.Add(new ProductModelProductDescriptionCultureMap()); modelBuilder.Configurations.Add(new ProductPhotoMap()); modelBuilder.Configurations.Add(new ProductProductPhotoMap()); modelBuilder.Configurations.Add(new ProductReviewMap()); modelBuilder.Configurations.Add(new ProductSubcategoryMap()); modelBuilder.Configurations.Add(new ScrapReasonMap()); modelBuilder.Configurations.Add(new TransactionHistoryMap()); modelBuilder.Configurations.Add(new TransactionHistoryArchiveMap()); modelBuilder.Configurations.Add(new UnitMeasureMap()); modelBuilder.Configurations.Add(new WorkOrderMap()); modelBuilder.Configurations.Add(new WorkOrderRoutingMap()); modelBuilder.Configurations.Add(new ProductVendorMap()); modelBuilder.Configurations.Add(new PurchaseOrderDetailMap()); modelBuilder.Configurations.Add(new PurchaseOrderHeaderMap()); modelBuilder.Configurations.Add(new ShipMethodMap()); modelBuilder.Configurations.Add(new VendorMap()); modelBuilder.Configurations.Add(new CountryRegionCurrencyMap()); modelBuilder.Configurations.Add(new CreditCardMap()); modelBuilder.Configurations.Add(new CurrencyMap()); modelBuilder.Configurations.Add(new CurrencyRateMap()); modelBuilder.Configurations.Add(new CustomerMap()); modelBuilder.Configurations.Add(new PersonCreditCardMap()); modelBuilder.Configurations.Add(new SalesOrderDetailMap()); modelBuilder.Configurations.Add(new SalesOrderHeaderMap()); modelBuilder.Configurations.Add(new SalesOrderHeaderSalesReasonMap()); modelBuilder.Configurations.Add(new SalesPersonMap()); modelBuilder.Configurations.Add(new SalesPersonQuotaHistoryMap()); modelBuilder.Configurations.Add(new SalesReasonMap()); modelBuilder.Configurations.Add(new SalesTaxRateMap()); modelBuilder.Configurations.Add(new SalesTerritoryMap()); modelBuilder.Configurations.Add(new SalesTerritoryHistoryMap()); modelBuilder.Configurations.Add(new ShoppingCartItemMap()); modelBuilder.Configurations.Add(new SpecialOfferMap()); modelBuilder.Configurations.Add(new SpecialOfferProductMap()); modelBuilder.Configurations.Add(new StoreMap()); modelBuilder.Configurations.Add(new vEmployeeMap()); modelBuilder.Configurations.Add(new vEmployeeDepartmentMap()); modelBuilder.Configurations.Add(new vEmployeeDepartmentHistoryMap()); modelBuilder.Configurations.Add(new vJobCandidateMap()); modelBuilder.Configurations.Add(new vJobCandidateEducationMap()); modelBuilder.Configurations.Add(new vJobCandidateEmploymentMap()); modelBuilder.Configurations.Add(new vAdditionalContactInfoMap()); modelBuilder.Configurations.Add(new vStateProvinceCountryRegionMap()); modelBuilder.Configurations.Add(new vProductAndDescriptionMap()); modelBuilder.Configurations.Add(new vProductModelCatalogDescriptionMap()); modelBuilder.Configurations.Add(new vProductModelInstructionMap()); modelBuilder.Configurations.Add(new vVendorWithAddressMap()); modelBuilder.Configurations.Add(new vVendorWithContactMap()); modelBuilder.Configurations.Add(new vIndividualCustomerMap()); modelBuilder.Configurations.Add(new vPersonDemographicMap()); modelBuilder.Configurations.Add(new vSalesPersonMap()); modelBuilder.Configurations.Add(new vSalesPersonSalesByFiscalYearMap()); modelBuilder.Configurations.Add(new vStoreWithAddressMap()); modelBuilder.Configurations.Add(new vStoreWithContactMap()); modelBuilder.Configurations.Add(new vStoreWithDemographicMap()); } }}
在项目中我们还可以看到Entity Framework Power Tools自动创建了一个Models文件夹，这里除了“AdventureWorksContext”类还有所有的数据类。在Models文件夹下还有一个“Mapping”文件夹，这里放了数据类与数据库的映射配置类，可以看出Entity Framework Power Tools通过fluent API的方式进行映射细节配置（目前Entity Framework Power Tools还不支持Data Annotations方式），关于配置类的具体细节我们这里暂不进行详细介绍。
下面我们进行数据查询：
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using EFPowerTools.Models;namespace EFPowerTools{ class Program { static void Main(string[] args) { using (var db = new AdventureWorksContext()) { var persons = db.People.Where(p => p.LastName == "Stevens").OrderBy(p=>p.FirstName); foreach(var p in persons) { Console.WriteLine("FirstName:{0},LastName:{1}", p.FirstName, p.LastName); } } } }} 查询结果：
自定义模板
事实上Entity Framework Power Tools的功能还远不止这些，例如我们上面谈到Entity Framework Power Tools使用fluent API进行映射配置，而通常情况下开发人员更喜欢使用Data Annotations方式进行映射约定，那么此时你就可以选择配置自己的模板。
在项目上右键选择Entity Frmaework->Customize Reverse Engineer Templates，此时会看到项目中添加了一个“CodeTemplates”文件夹，里面存放了Entity Framework Power Tools用于生产相关类文件的T4模板（对于不了解T4模板引擎的朋友可以点击这里），如果此时再使用Entity Framework Power Tools进行Code First反向工程操作将使用当前这个文件夹中的模板进行生成。接下来看一下如何进行模板自定义。
首先让我们打开Mapping.tt文件，这个文件主要用户生成配置类，在Entity Framework Power Tools默认生成的代码中通过fluent API进行表名和数据类名以及属性名同列名的对应配置，例如下面的代码：
下面让我们修改一下Mapping.tt文件，去掉上面的约束，而改用Data Annotations方式进行约定。首先去掉下图中选择的代码，此时生成的映射类中就不再出现上图中选择的代码部分：
然后我们需要修改Entity.tt模板，将数据库中的表和列的映射声明到数据类上。先让我们将数据类和表做对应，这需要在数据类上添加“Table”声明，标记出表名和架构名（EF默认会使用dbo架构），在如图位置添加如下代码：
<# var tableName = (string)efHost.TableSet.MetadataProperties["Table"].Value ?? efHost.TableSet.Name; var conventionTableName = System.Data.Entity.Design.PluralizationServices.PluralizationService .CreateService(new CultureInfo("en")) .Pluralize(efHost.EntityType.Name); var schemaName = (string)efHost.TableSet.MetadataProperties["Schema"].Value; schemaName = string.IsNullOrWhiteSpace(schemaName) ? "dbo" : schemaName; if(schemaName != "dbo" || conventionTableName != tableName) { #> [Table("<#= tableName #>", Schema="<#= schemaName #>")] <# }#> 这段代码主要处理逻辑是：当架构不是“dbo”或者表名的复数形式同表名不同时添加“Table”标记声明。之所以添加判断是因为EF的默认使用“dbo”架构并且EF在操作表的时候默认将数据类的复数形式作为表名。
接下来添加列标记声明，在如图位置添加如下代码即可：
var columnName = efHost.PropertyToColumnMappings[property].Name; if(code.Escape(property) != columnName) { #> [Column("<#= columnName #>")] <# } 这里只是简单的对列名和编码后的列名进行比较，不同则添加列标记，否则不添加（EF默认认为数据类属性名和表的列名相同）。
由于刚才添加的标记属性类在“System.ComponentModel.DataAnnotations.Schema” 命名空间下，因此最后还需要在模板头部添加该命名空间：
<# if (efHost.EntityFrameworkVersion >= new Version(4, 4)) { #> using System.ComponentModel.DataAnnotations.Schema; <# } else { #> using System.ComponentModel.DataAnnotations; <# } #> 由于之前的EF版本中“Table”和“Column”类不在“System.ComponentModel.DataAnnotations.Schema”命名空间而是在 “System.ComponentModel.DataAnnotations”命名空间中，因此这里我们还需要添加一个判断。
今天的内容先到此为止，关于如何使用fluent API及Data Annotations定义配置类来进行更多的映射控制请关注后面的文章。