EntityFramework系列：SQLite的CodeFrist和RowVersion

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。

1.首先是RowVersion的配置：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove();
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));
}

2.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();
}

3.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();
modelBuilder.Entity().ToTable(DefaultTableName);
modelBuilder.Entity().HasKey(
h => new
{
h.MigrationId,
h.ContextKey
});
modelBuilder.Entity().Property(h => h.MigrationId).HasMaxLength(MigrationIdMaxLength).IsRequired();
modelBuilder.Entity().Property(h => h.ContextKey).HasMaxLength(ContextKeyMaxLength).IsRequired();
modelBuilder.Entity().Property(h => h.Model).IsRequired().IsMaxLength();
modelBuilder.Entity().Property(h => h.ProductVersion).HasMaxLength(32).IsRequired();
}

4.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().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;
}
}
}

5.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().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。

6.不修改源代码，使用反射实现

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：

using SQLite.CodeFirst.Statement;
using System;
using System.Data.Entity;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.Migrations.History;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.IO;
using System.Linq;
using System.Reflection;
namespace SQLite.CodeFirst
{
public class SqliteDropCreateDatabaseIfModelChanges : IDatabaseInitializer where TContext : DbContext
{
protected readonly DbModelBuilder ModelBuilder;
protected readonly string DatabaseFilePath;
public const string DefaultTableName = "__MigrationHistory";
private const string DataDirectoryToken = "|datadirectory|";
internal const int COntextKeyMaxLength= 300;
internal const int MigratiOnIdMaxLength= 150;
public SqliteDropCreateDatabaseIfModelChanges(string connectionString, DbModelBuilder modelBuilder)
{
DatabaseFilePath = ConnectionStringParse(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();
ConfigMigrationHistory(modelBuilder);
}
private string ConnectionStringParse(string connectionString)
{
var path = connectionString.Trim(' ', ';').Split(';').FirstOrDefault(o => o.StartsWith("data source", StringComparison.OrdinalIgnoreCase)).Split('=').Last().Trim();
if (!path.StartsWith("|datadirectory|", StringComparison.OrdinalIgnoreCase))
{
return path;
}
string fullPath;
// find the replacement path
object rootFolderObject = AppDomain.CurrentDomain.GetData("DataDirectory");
string rootFolderPath = (rootFolderObject as string);
if (rootFolderObject != null && rootFolderPath == null)
{
throw new InvalidOperationException("The value stored in the AppDomains 'DataDirectory' variable has to be a string!");
}
if (string.IsNullOrEmpty(rootFolderPath))
{
rootFolderPath = AppDomain.CurrentDomain.BaseDirectory;
}
// We don't know if rootFolderpath ends with '\', and we don't know if the given name starts with onw
int fileNamePosition = DataDirectoryToken.Length; // filename starts right after the '|datadirectory|' keyword
bool rootFolderEndsWith = (0 1] == '\\';
bool fileNameStartsWith = (fileNamePosition '\\';
// replace |datadirectory| with root folder path
if (!rootFolderEndsWith && !fileNameStartsWith)
{
// need to insert '\'
fullPath = rootFolderPath + '\\' + path.Substring(fileNamePosition);
}
else if (rootFolderEndsWith && fileNameStartsWith)
{
// need to strip one out
fullPath = rootFolderPath + path.Substring(fileNamePosition + 1);
}
else
{
// simply concatenate the strings
fullPath = rootFolderPath + path.Substring(fileNamePosition);
}
return fullPath;
}
private void ConfigMigrationHistory(DbModelBuilder modelBuilder)
{
modelBuilder.Entity().ToTable(DefaultTableName);
modelBuilder.Entity().HasKey(
h => new
{
h.MigrationId,
h.ContextKey
});
modelBuilder.Entity().Property(h => h.MigrationId).HasMaxLength(MigrationIdMaxLength).IsRequired();
modelBuilder.Entity().Property(h => h.ContextKey).HasMaxLength(ContextKeyMaxLength).IsRequired();
modelBuilder.Entity().Property(h => h.Model).IsRequired().IsMaxLength();
modelBuilder.Entity().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().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
{
sqliteDatabaseCreator.Create();
transaction.Commit();
}
catch (Exception)
{
transaction.Rollback();
throw;
}
}
using (var transaction = context.Database.BeginTransaction())
{
try
{
context.Set().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"
});
Seed(context);
context.SaveChanges();
transaction.Commit();
}
catch (Exception)
{
transaction.Rollback();
throw;
}
}
}
protected virtual void Seed(TContext context)
{
}
}
}

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希望你不是找了好久才找到这个解决方案。