没什么好说的，能支持DropCreateDatabaseIfModelChanges和RowVersion的Sqlite谁都想要。EntityFramework7正在添加对Sqlite的支持，虽然EF7不知道猴年马月才能完成正式版，更不知道MySql等第三方提供程序会在什么时候跟进支持，但是EF7中的确出现了Sqlite的相关代码。Sqlite支持EF6的CodeFirst，只是不支持从实体生成数据库，估计有很多人因为这个原因放弃了使用它。现在SQLite.CodeFirst的简单实现可以让我们生成数据库，因此在等待EF7的可以预见的长时间等待中，我们可以使用SQLite.CodeFirst，毕竟我们只是开发的时候使用DropCreateDatabaseIfModelChanges，Release时不会使用更不用担心SQLite.CodeFirst的简单实现会带来什么问题。可以直接修改源码，也可以参考最后面通过反射实现自定义DropCreateDatabaseIfModelChanges的方式。
1.RowVersion的支持：
可以从我的上一篇：在MySql中使用和SqlServer一致的RowVersion并发控制中采用相同的策略即可。我已经测试过在Sqlite中的可行性。
首先是RowVersion的配置：
protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); modelBuilder.Configurations.AddFromAssembly(typeof(SqliteDbContext).Assembly); modelBuilder.Properties() .Where(o => o.Name == "RowVersion") .Configure(o => o.IsConcurrencyToken() .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None)); Database.SetInitializer(new SqliteDbInitializer(Database.Connection.ConnectionString, modelBuilder)); }然后是SaveChanges的重写：
public override int SaveChanges() { this.ChangeTracker.DetectChanges(); var objectContext = ((IObjectContextAdapter)this).ObjectContext; foreach (ObjectStateEntry entry in objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Modified | EntityState.Added)) { var v = entry.Entity as IRowVersion; if (v != null) { v.RowVersion = System.Text.Encoding.UTF8.GetBytes(Guid.NewGuid().ToString()); } } return base.SaveChanges(); }2.DropCreateDatabaseIfModelChanges支持
（1）生成__MigrationHistory：
DropCreateDatabaseIfModelChanges则需要修改SQLite.CodeFirst的代码，SQLite.CodeFirst生成的数据库不包含__MigrationHistory信息，所以我们首先修改SqliteInitializerBase添加__MigrationHistory，__MigrationHistory表是通过HistoryRow实体的映射，我们直接在EF源代码中找到相关部分作为参考。修改SqliteInitializerBase的SqliteInitializerBase方法，配置HistoryRow实体的映射。
public const string DefaultTableName = "__MigrationHistory"; internal const int ContextKeyMaxLength = 300; internal const int MigrationIdMaxLength = 150; protected SqliteInitializerBase(string connectionString, DbModelBuilder modelBuilder) { DatabaseFilePath = SqliteConnectionStringParser.GetDataSource(connectionString); ModelBuilder = modelBuilder; // This convention will crash the SQLite Provider before "InitializeDatabase" gets called. // See https://github.com/msallin/SQLiteCodeFirst/issues/7 for details. modelBuilder.Conventions.Remove<TimestampAttributeConvention>(); modelBuilder.Entity<HistoryRow>().ToTable(DefaultTableName); modelBuilder.Entity<HistoryRow>().HasKey( h => new { h.MigrationId, h.ContextKey }); modelBuilder.Entity<HistoryRow>().Property(h => h.MigrationId).HasMaxLength(MigrationIdMaxLength).IsRequired(); modelBuilder.Entity<HistoryRow>().Property(h => h.ContextKey).HasMaxLength(ContextKeyMaxLength).IsRequired(); modelBuilder.Entity<HistoryRow>().Property(h => h.Model).IsRequired().IsMaxLength(); modelBuilder.Entity<HistoryRow>().Property(h => h.ProductVersion).HasMaxLength(32).IsRequired(); }（2）初始化__MigrationHistory：
继续修改InitializeDatabase方法，在创建数据库后，初始化__MigrationHistory的信息。虽然采用了HistoryRow，但初始化信息我们只简单的使用生成的SQL语句作为判定实体和配置是否改变的依据，因为后面的InitializeDatabase方法中也是我们自己来判定实体和配置是否改变。
public virtual void InitializeDatabase(TContext context) { var model = ModelBuilder.Build(context.Database.Connection); using (var transaction = context.Database.BeginTransaction()) { try { var sqliteDatabaseCreator = new SqliteDatabaseCreator(context.Database, model); sqliteDatabaseCreator.Create(); /*start*/ context.Set<HistoryRow>().Add( new HistoryRow { MigrationId = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:fffffff"), ContextKey = context.GetType().FullName, Model = System.Text.Encoding.UTF8.GetBytes(sqliteDatabaseCreator.GetSql().ToCharArray()), ProductVersion = "6.1.2" }); /*end*/ transaction.Commit(); } catch (Exception) { transaction.Rollback(); throw; } } using (var transaction = context.Database.BeginTransaction()) { try { Seed(context); context.SaveChanges(); transaction.Commit(); } catch (Exception) { transaction.Rollback(); throw; } } }（3）添加DropCreateDatabaseIfModelChanges支持
添加SqliteDropCreateDatabaseIfModelChanges类，在InitializeDatabase方法中判读实体和配置是否改变。需要注意的是，删除sqlite文件时，即使关闭Connection和调用GC.Collect()仍然在第一次无法删除文件，所以必须进行多次尝试。
public override void InitializeDatabase(TContext context) { bool dbExists = File.Exists(DatabaseFilePath); if (dbExists) { var model = ModelBuilder.Build(context.Database.Connection); var sqliteDatabaseCreator = new SqliteDatabaseCreator(context.Database, model); var newSql = sqliteDatabaseCreator.GetSql(); var oldSql = ""; oldSql = System.Text.Encoding.UTF8.GetString(context.Set<System.Data.Entity.Migrations.History.HistoryRow>().AsNoTracking().FirstOrDefault().Model); context.Database.Connection.Close(); GC.Collect(); if (oldSql == newSql) { return; } for (int i = 0; i < 10; i++) { try { File.Delete(DatabaseFilePath); break; } catch (Exception) { System.Threading.Thread.Sleep(1); } } } base.InitializeDatabase(context); }
核心的代码已经贴出来，SQLite.CodeFirst本身的实现就比较简易，我添加的代码也比较简陋，因此在代码上没什么参考价值，只有使用和实用价值。毕竟只是在Debug开发时才需要这些功能的支持，对Sqlite本身和EF的提供程序没有任何影响。到这里终于松了口气，我们现在可以使用：Sql Server（CE）、Sqlite和Mysql进行Code First开发，采用相同的实体定义和配置，并且采用相同的并发控制。非Sql Server（CE）的并发控制和Sqlite不支持从代码生成数据库这两点终于克服了。
后记
修改源码是由于SQLite.CodeFirst的内部类无法调用，考虑到可以使用反射，于是有了下面不需要修改源码，通过反射实现直接自定义DropCreateDatabaseIfModelChanges的方式：
public class SqliteDropCreateDatabaseIfModelChanges<TContext> : IDatabaseInitializer<TContext> where TContext : DbContext { protected readonly DbModelBuilder ModelBuilder; protected readonly string DatabaseFilePath; public const string DefaultTableName = "__MigrationHistory"; internal const int ContextKeyMaxLength = 300; internal const int MigrationIdMaxLength = 150; public SqliteDropCreateDatabaseIfModelChanges(string connectionString, DbModelBuilder modelBuilder) { ModelBuilder = modelBuilder; ConfigMigrationHistory(modelBuilder); } private void ConfigMigrationHistory(DbModelBuilder modelBuilder) { modelBuilder.Entity<HistoryRow>().ToTable(DefaultTableName); modelBuilder.Entity<HistoryRow>().HasKey( h => new { h.MigrationId, h.ContextKey }); modelBuilder.Entity<HistoryRow>().Property(h => h.MigrationId).HasMaxLength(MigrationIdMaxLength).IsRequired(); modelBuilder.Entity<HistoryRow>().Property(h => h.ContextKey).HasMaxLength(ContextKeyMaxLength).IsRequired(); modelBuilder.Entity<HistoryRow>().Property(h => h.Model).IsRequired().IsMaxLength(); modelBuilder.Entity<HistoryRow>().Property(h => h.ProductVersion).HasMaxLength(32).IsRequired(); } public string GetSql(DbModel model) { Assembly asm = Assembly.GetAssembly(typeof(SqliteInitializerBase<>)); Type builderType = asm.GetType("SQLite.CodeFirst.Builder.CreateDatabaseStatementBuilder"); ConstructorInfo builderConstructor = builderType.GetConstructor(new Type[] { typeof(EdmModel) }); Object builder = builderConstructor.Invoke(new Object[] { model.StoreModel }); MethodInfo method = builderType.GetMethod("BuildStatement", BindingFlags.Instance|BindingFlags.InvokeMethod|BindingFlags.Public); var statement = (IStatement)method.Invoke(builder, new Object[] { }); string sql = statement.CreateStatement(); return sql; } public void InitializeDatabase(TContext context) { var model = ModelBuilder.Build(context.Database.Connection); var sqliteDatabaseCreator = new SqliteDatabaseCreator(context.Database, model); var newSql = this.GetSql(model); bool dbExists = File.Exists(DatabaseFilePath); if (dbExists) { var oldSql = System.Text.Encoding.UTF8.GetString(context.Set<System.Data.Entity.Migrations.History.HistoryRow>().AsNoTracking().FirstOrDefault().Model); context.Database.Connection.Close(); GC.Collect(); if (oldSql == newSql) { return; } for (int i = 0; i < 10; i++) { try { File.Delete(DatabaseFilePath); break; } catch (Exception) { System.Threading.Thread.Sleep(1); } } } using (var transaction = context.Database.BeginTransaction()) { try { context.Database.ExecuteSqlCommand(newSql); context.Set<HistoryRow>().Add( new HistoryRow { MigrationId = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:fffffff"), ContextKey = context.GetType().FullName, Model = System.Text.Encoding.UTF8.GetBytes(newSql.ToCharArray()), ProductVersion = "6.1.3" }); transaction.Commit(); } catch (Exception) { transaction.Rollback(); throw; } } using (var transaction = context.Database.BeginTransaction()) { try { Seed(context); context.SaveChanges(); transaction.Commit(); } catch (Exception) { transaction.Rollback(); throw; } } } protected virtual void Seed(TContext context) { } }View Code
希望你不是找了好久才找到这个解决方案。
原标题：Entity Framework 6 Code First 系列：使SQLite.CodeFirst支持DropCreateDatabaseIfModelChanges和RowVersion
关键词：sql
我知道了 