Question

在我的项目中尝试实施EF迁移时，我被困在一个地方。

EF Code First MigrateDatabaseToLatestVersion接受来自config的连接字符串Name。

在我的案例中，数据库名称在运行时已知（用户从下拉列表中选择它）。就像DbContext接受的方式，ConnectionString或connectionString Name在它的构造函数中，“MigrateDatabaseToLatestVersion”不接受相同的

System.Data.Entity.Database.SetInitializer
(new MigrateDatabaseToLatestVersion<SrcDbContext, SRC.DomainModel.ORMapping.Migrations.Configuration>(connString));

还有其他方法可以达到这个目的吗？

Answer 1

谢谢大家。我从codeplex中检出了EF代码，并在理解了它们的源代码后继承了我自己的类。这是我选择的解决方案： -

public class MigrateDbToLatestInitializerConnString<TContext, TMigrationsConfiguration> : IDatabaseInitializer<TContext>
        where TContext : DbContext
        where TMigrationsConfiguration : DbMigrationsConfiguration<TContext>, new()
    {
        private readonly DbMigrationsConfiguration config;

        /// <summary>
        ///     Initializes a new instance of the MigrateDatabaseToLatestVersion class.
        /// </summary>
        public MigrateDbToLatestInitializerConnString()
        {
            config = new TMigrationsConfiguration();
        }

        /// <summary>
        ///     Initializes a new instance of the MigrateDatabaseToLatestVersion class that will
        ///     use a specific connection string from the configuration file to connect to
        ///     the database to perform the migration.
        /// </summary>
        /// <param name="connectionString"> connection string to use for migration. </param>
        public MigrateDbToLatestInitializerConnString(string connectionString)
        {
            config = new TMigrationsConfiguration
                          {
                              TargetDatabase = new DbConnectionInfo(connectionString, "System.Data.SqlClient")
                          };
        }

        public void InitializeDatabase(TContext context)
        {
            if (context == null)
            {
                throw new ArgumentException("Context passed to InitializeDatabase can not be null");
            }

            var migrator = new DbMigrator(config);

            migrator.Update();
        }
    }

 public static class DatabaseHelper
    {
        /// <summary>
        /// This method will create data base for given parameters supplied by caller.
        /// </summary>
        /// <param name="serverName">Name of the server where database has to be created</param>
        /// <param name="databaseName">Name of database</param>
        /// <param name="userName">SQL user name</param>
        /// <param name="password">SQL password</param>
        /// <returns>void</returns>
        public static bool CreateDb(string serverName, string databaseName, string userName, string password)
        {
            bool integratedSecurity = !(!string.IsNullOrEmpty(userName) || !string.IsNullOrEmpty(password));

            var builder = new System.Data.SqlClient.SqlConnectionStringBuilder
                {
                    DataSource = serverName,
                    UserID = userName,
                    Password = password,
                    InitialCatalog = databaseName,
                    IntegratedSecurity = integratedSecurity,
                };


            var db = new SrcDbContext(builder.ConnectionString);

            var dbInitializer = new MigrateDbToLatestInitializerConnString<SrcDbContext, SRC.DomainModel.ORMapping.Migrations.Configuration>(builder.ConnectionString);

            //following uses strategy to "CreateIfNotExist<>"
            dbInitializer.InitializeDatabase(db);

            return true;

        }
    }

Answer 2

这是在什么情况下运行？网站或桌面应用程序？

在网站下，这样做并不是一个好主意。数据库初始化策略根据上下文类型设置。因此，具有相同类型上下文的不同连接字符串将覆盖彼此的init策略。

如果桌面应用程序，可能包含一个额外的实用程序来在数据库之间切换？

无论哪种方式，我都不建议这样做，但如果你真的想做你提到的事情，看起来你必须破解它。

    using (var context = new DbContext("<Your connection string right in here>"))
    {
        var constructors = typeof (DbMigrator).GetConstructors(BindingFlags.Instance | BindingFlags.NonPublic);
        var hackedDbMigrator = constructors[0].Invoke(new object[] { new Configuration(), context }) as DbMigrator;
        hackedDbMigrator.Update();
    }

Answer 3

您可以使 MigrateDatabaseToLatestVersion 初始化程序使用首先触发迁移的上下文使用的连接字符串。这是通过将 useSuppliedContext：true 传递给MigrateDatabaseToLatestVersion构造函数来完成的，如the docs中所述。在你的情况下：

Database.SetInitializer(new MigrateDatabaseToLatestVersion<SrcDbContext, SRC.DomainModel.ORMapping.Migrations.Configuration>(useSuppliedContext: true));

Answer 4

迁移的问题是使用参数调用DbContext派生类。一旦解决了它应该工作。请看这里的示例解决方案。 EntityFramework code-first custom connection string and migrations

EF Code First MigrateDatabaseToLatestVersion接受来自config的连接字符串Name

4 个答案: