c# - SQLite.CodeFirst - 创建模型时无法使用上下文

Question

我正在使用带有 SQLite 数据库的 WPF 应用程序。尝试使用 SQLite.CodeFirst 以代码优先的方式设计数据库。

错误是:{“创建模型时无法使用上下文。如果在OnModelCreating方法内部使用了上下文，或者如果多个线程同时访问同一个上下文实例，则可能会抛出此异常。注意不保证 DbContext 和相关类的实例成员是线程安全的。”

我正在使用代码:

1. 数据库上下文:

   class GestDbContext : DbContext
   {
       override protected void OnModelCreating(DbModelBuilder modelBuilder)
       {
           var model = modelBuilder.Build(Database.Connection);
           IDatabaseCreator sqliteDatabaseCreator = new SqliteDatabaseCreator();
           sqliteDatabaseCreator.Create(Database, model);
       }
   
       public DbSet<GestUser> GestUsers { get; set; }
       public DbSet<Gesture> Gestures { get; set; }
       public DbSet<UserSettings> UserSettings { get; set; }
   
   }
   

2. MainWindowViewModel - 只是为了初始化数据库

   #region Constructor
   public MainWindowViewModel()
   {
       using (var context = new GestDbContext())
       {
           var entity = context.Gestures.Any();
       }
   }
   #endregion
   

3. 应用程序配置

   <entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
<parameters>
<parameter value="mssqllocaldb" />
</parameters>
</defaultConnectionFactory>
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
<provider invariantName="System.Data.SQLite.EF6" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" />
<provider invariantName="System.Data.SQLite" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" />
</providers>
</entityFramework>
<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" />
</DbProviderFactories>
</system.data>
<connectionStrings>
<add name="connection"
connectionString="Data Source=.\GestDB"
providerName="System.Data.SqlLite"/>
</connectionStrings>

Answer 1

我将 modelBuilder 从 OnModelCreating 保存在一个实例变量中

private DbModelBuilder _modelBuilder;
override protected void OnModelCreating(DbModelBuilder modelBuilder)
{
    _modelBuilder = modelBuilder;
}

然后在公共(public)方法中使用它:

public void Init()
{
  var model = _modelBuilder.Build(Database.Connection);
  IDatabaseCreator sqliteDatabaseCreator = new SqliteDatabaseCreator();
  sqliteDatabaseCreator.Create(Database, model);
}

并执行一次(我需要创建一次结构)

public MainWindowViewModel()
{
  using (var context = new GestDbContext())
  {
    var entity = context.Gestures.Any();
    context.Init();
  }
}