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目前 EF 是 .NET 平台下相当成熟的 ORM 框架，但是其最新发布的 6.x 版本依然不支持 SQLite 的 CodeFirst 模式，好在有大神已经在 Nuget 上发布的相应的 Package 来解决这个问题。笔者通过做一个小实验来验证一下。
SQLite 本身不支持 CodeFirst 模式，当我们的数据模型因业务变化而需要修改的话，那对应的数据库表也要进行更改。这个时候，如果我们手动修改数据表的话就不太方便，因此我们需要想办法让其支持 CodeFirst 模式。笔者通过使用 SQLite.CodeFirst 来尝试解决上述问题。
首先我们创建一个控制台程序，安装如下 Package：
- System.Data.SQLite
- SQLite.CodeFirst
<?xml version="1.0" encoding="utf-8"?> <configuration> <configSections> <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 --> <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" /> </configSections> <startup> <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" /> </startup> <!--新增结点--> <system.data> <DbProviderFactories> <remove invariant="System.Data.SQLite.EF6" /> <add name="SQLite Data Provider (Entity Framework 6)" invariant="System.Data.SQLite.EF6" description=".NET Framework Data Provider for SQLite (Entity Framework 6)" type="System.Data.SQLite.EF6.SQLiteProviderFactory, System.Data.SQLite.EF6" /> <remove invariant="System.Data.SQLite" /><add name="SQLite Data Provider" invariant="System.Data.SQLite" description=".NET Framework Data Provider for SQLite" type="System.Data.SQLite.SQLiteFactory, System.Data.SQLite" /></DbProviderFactories> </system.data> <entityFramework> <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework"> <parameters> <parameter value="mssqllocaldb" /> </parameters> </defaultConnectionFactory> <!--新增结点--> <providers> <provider invariantName="System.Data.SQLite" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" /> <provider invariantName="System.Data.SQLite.EF6" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" /> </providers> </entityFramework> <!--新增结点--> <connectionStrings> <add name="sampledb" connectionString="data source=.\sampledb.db" providerName="System.Data.SQLite" /> </connectionStrings> </configuration>
[Table("person")] public class Person { [Column("id"), Key, Autoincrement] public int Id { get; set; } [Column("firstname")] public string FirstName { get; set; } [Column("lastname")] public string LastName { get; set; } } public class PersonDbContext : DbContext { public DbSet<Person> People { get; set; } /// <summary> /// 从配置文件读取链接字符串 /// </summary> public PersonDbContext() : base("name = sampledb") { ConfigurationFunc(); } /// <summary> /// 代码指定数据库连接 /// </summary> /// <param name="existingConnection"></param> /// <param name="contextOwnsConnection"></param> public PersonDbContext(DbConnection existingConnection, bool contextOwnsConnection) : base(existingConnection, contextOwnsConnection) { ConfigurationFunc(); } private void ConfigurationFunc() { Configuration.LazyLoadingEnabled = true; Configuration.ProxyCreationEnabled = true; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { var initializer = new SqliteDropCreateDatabaseWhenModelChanges<PersonDbContext>(modelBuilder); Database.SetInitializer(initializer); } } 此时，当我们修改数据模型时，不需要执行任何 migration 操作就可以将 数据表映射到新的模型上。下面我们在主程序中调用一下：
class Program { static void Main(string[] args) { var ptah = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "sampledb.db"); var connection = SQLiteProviderFactory.Instance.CreateConnection(); connection.ConnectionString = $"Data Source={ptah}"; //using (var context = new PersonDbContext()) using (var context = new PersonDbContext(connection, false)) { #region 预热：针对数据表较多的情况下建议执行下述操作 var objectContext = ((IObjectContextAdapter)context).ObjectContext; var mappingColection = (StorageMappingItemCollection)objectContext.MetadataWorkspace.GetItemCollection(DataSpace.CSSpace); mappingColection.GenerateViews(new List<EdmSchemaError>()); #endregion #region 插入数据 Console.WriteLine("插入数据："); context.People.Add(new Person { FirstName = "hippie", LastName = "zhou" }); context.SaveChanges(); #endregion #region 查找数据 Console.WriteLine("查找数据："); foreach (var people in context.People) { Console.WriteLine($"{people.Id} - {people.FirstName} - {people.LastName}"); } #endregion #region 更改数据 Console.WriteLine("更改数据："); Person person = context.People.Where(p => p.Id == 1)?.FirstOrDefault(); person.LastName = "Puth"; context.SaveChanges(); #endregion #region 删除数据 Console.WriteLine("删除数据："); Person person = context.People.Where(p => p.Id == 1)?.FirstOrDefault(); context.People.Remove(person); context.SaveChanges(); #endregion Console.ReadKey(); } } } 由于 SQLite.CodeFirst 的 Package 需要依赖 EntityFramework,以及为了能保证数据操作支持异步性，在上述两个 Pacakge 安装的过程中，会同时安装其它依赖包，所以最终的项目依赖包如下所示：
- EntityFramework
- SQLite.CodeFirst
- System.Data.SQLite
- System.Data.SQLite.Core
- System.Data.SQLite.EF6
- System.Data.SQLite.Linq
此外，需要注意一下 System.Data.SQLite 与 System.Data.SQLite.Core 的区别：
System.Data.SQLite：The official SQLite database engine for both x86 and x64 along with the ADO.NET provider. This package includes support for LINQ and Entity Framework 6.
System.Data.SQLite.Core：The official SQLite database engine for both x86 and x64 along with the ADO.NET provider.
所以，为了能让 SQLite 支持 CodeFirst ,还是一件挺曲折的事情啊。