目录
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。
问题描述
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。
解决方案
安装依赖包
首先我们创建一个控制台程序,安装如下 Package:
- System.Data.SQLite
- SQLite.CodeFirst
修改程序配置 App.config
<?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>
创建模型对象 Person.cs
[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; }
}
创建数据上下文 PersonDbContext.cs
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:
主程序调用 Program.cs
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();
}
}
}
注意事项
由于 SQLite.CodeFirst 的 Package 需要依赖 EntityFramework
,以及为了能保证数据操作支持相关 LINQ 操作,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。