如何添加一个新生成的数据库中的新代码优先迁移？(How to add a new code-firs

2019-08-02 01:36发布

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我已经启用了我的实体框架项目代码优先迁移，并增加了一些迁移该做的事情一样重命名表。 不过，我现在已经删除了数据库，并造成实体框架，基于我的最新数据模型，一个全新的数据库。 如果我尝试运行： 

PM> Add-Migration TestMigration

......它告诉我，我需要首先将现有的迁移。 于是我运行： 

PM> Update-Database

......但麻烦的是，它试图更新不需要更新数据库; 它已经基于最新的数据模型。 所以，当它试图重新命名，现在不存在的表，我得到一个错误。

有没有一些方法，我可以指示数据迁移，我的数据库运行最新的，并不需要在其上运行任何迁移？ 我该怎么办？

Answer 1:

我已经找到了一种方法，以表明我的数据库是最新的最新的，和它的（不出所料）的基础上修改__MigrationHistory表，代码优先迁移用来确定当你运行应用到DB哪些迁移Update-Database 。

顺便说一句，同时研究这个答案我碰到一个很不错的参考来对代码优先迁移命令，可以在这里找到： http://dotnet.dzone.com/articles/ef-migrations-command

当从头开始自动EF创建的数据库，它会永远把一个进入__MigrationHistory表，该条目将有MigrationId (currentDateTime)_InitialCreate 。 这表示EF刚刚进行过数据库的初始创建。 但是，迁移历史是不会与MigrationId开始，因为你已经开始用别的东西。

以“傻瓜”代码优先迁移，以为你是在最新的迁移，您需要删除(currentDateTime)_InitialCreate从入门__MigrationHistory新创建数据库的表，然后将你会一直存在，如果你仍然有旧的数据库，其不得不适用于它的迁移。

所以，先删除一切从新近生成的DB的__MigrationHistory表。 然后，进入包管理器控制台，然后运行： 

PM> Update-Database -Script

从得到的SQL脚本，使出浑身开头的几行： 

INSERT INTO [__MigrationHistory]...

然后，运行这些INSERT新创建的数据库的上下文中的语句。 检查每个这些行现在在你的存在__MigrationHistory表。 当您下一次运行： 

PM> Update-Database

......你应该得到一个消息，说“没有待基于代码的迁移。” 恭喜 - 你已经上当代码优先迁移以为你现在最新的迁移，你可以继续你离开的地方离这里添加新的迁移。

我认为应该有做着这个内置EF代码优先，但...也许还应该加上一些像一些自动化的方式： 

PM> Update-Database -MigrationsTableOnly

......由此会揍在迁移表中的现有条目，只需将新的条目到迁移历史记录在您的项目中定义的每个迁移，但实际上没有尝试和执行的迁移。 呃，好吧。

UPDATE
我已经找到一种方法来很好地自动执行此，使用自定义初始化的种子法。 基本上种子方法删除DB时，被创建的现有迁移历史数据，并插入您的迁移历史。 在我的数据库上下文构造，我注册自定义初始化像这样： 

public class MyDatabaseContext : DbContext {
    public MyDatabaseContext() : base() {
        Database.SetInitializer(new MyDatabaseContextMigrationHistoryInitializer());
    }

自定义初始化本身看起来是这样的： 

/// <summary>
/// This initializer clears the __MigrationHistory table contents created by EF code-first when it first
/// generates the database, and inserts all the migration history entries for migrations that have been
/// created in this project, indicating to EF code-first data migrations that the database is
/// "up-to-date" and that no migrations need to be run when "Update-Database" is run, because we're
/// already at the latest schema by virtue of the fact that the database has just been created from
/// scratch using the latest schema.
/// 
/// The Seed method needs to be updated each time a new migration is added with "Add-Migration".  In
/// the package manager console, run "Update-Database -Script", and in the SQL script which is generated,
/// find the INSERT statement that inserts the row for that new migration into the __MigrationHistory
/// table.  Add that INSERT statement as a new "ExecuteSqlCommand" to the end of the Seed method.
/// </summary>
public class MyDatabaseContextMigrationHistoryInitializer : CreateDatabaseIfNotExists<MyDatabaseContext> {
    /// <summary>
    /// Sets up this context's migration history with the entries for all migrations that have been created in this project.
    /// </summary>
    /// <param name="context">The context of the database in which the seed code is to be executed.</param>
    protected override void Seed(MyDatabaseContext context) {
        // Delete existing content from migration history table, and insert our project's migrations
        context.Database.ExecuteSqlCommand("DELETE FROM __MigrationHistory");
        context.Database.ExecuteSqlCommand("INSERT INTO __MigrationHistory (MigrationId, Model, ProductVersion) VALUES ('201210091606260_InitialCreate', 0x1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4AF54AD7E074A..., '5.0.0.net40')");
        context.Database.ExecuteSqlCommand("INSERT INTO __MigrationHistory (MigrationId, Model, ProductVersion) VALUES ('201210102218467_MakeConceptUserIdNullable', 0x1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4..., '5.0.0.net40')");
        context.Database.ExecuteSqlCommand("INSERT INTO __MigrationHistory (MigrationId, Model, ProductVersion) VALUES ('201210231418163_ChangeDateTimesToDateTimeOffsets', 0x1F8B0800000000000400ECBD07601C499625262F6D..., '5.0.0.net40')");
        context.Database.ExecuteSqlCommand("INSERT INTO __MigrationHistory (MigrationId, Model, ProductVersion) VALUES ('201210251833252_AddConfigSettings', 0x1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4AF54AD7E..., '5.0.0.net40')");
        context.Database.ExecuteSqlCommand("INSERT INTO __MigrationHistory (MigrationId, Model, ProductVersion) VALUES ('201210260822485_RenamingOfSomeEntities', 0x1F8B0800000000000400ECBD07601C499625262F6DCA7B7F4AF5..., '5.0.0.net40')");
    }
}


Answer 2:

转到MigrationHistory在SQL Server（下表system文件夹），它具有排了迁移，并在其数据库哈希必须是同一个在迁移文件，只是从数据库到文件复制。

换句话说，你需要同步您的MigrationHistory实际迁移表。



Answer 3:

此实现不需要手工维护的记录被插入到__MigrationHistory 。 迁移是从组件指定的确定。

也许这会有所帮助。

我感谢送给@Jez了最初的想法。 

/// <summary>
/// An implementation of IDatabaseInitializer that will:
/// 1. recreate database only if the database does not exist 
/// 2. actualize __MigrationHistory to match current model state (i.e. latest migration)
/// </summary>
/// <typeparam name="TContext">The type of the context.</typeparam>
public class CreateDatabaseIfNotExistsAndMigrateToLatest<TContext> : CreateDatabaseIfNotExists<TContext>
    where TContext : DbContext
{
    private readonly Assembly migrationsAssembly;

    /// <summary>
    /// Gets the migration metadata for types retrieved from <paramref name="assembly"/>. Types must implement <see cref="IMigrationMetadata"/>.
    /// </summary>
    /// <param name="assembly">The assembly.</param>
    /// <returns></returns>
    private static IEnumerable<IMigrationMetadata> GetMigrationMetadata(Assembly assembly)
    {
        var types = assembly.GetTypes().Where(t => typeof(IMigrationMetadata).IsAssignableFrom(t));
        var migrationMetadata = new List<IMigrationMetadata>();
        foreach (var type in types)
        {
            migrationMetadata.Add(
                (IMigrationMetadata)Activator.CreateInstance(type));
        }

        return migrationMetadata.OrderBy(m => m.Id);
    }

    /// <summary>
    /// Gets the provider manifest token.
    /// </summary>
    /// <param name="db">The db.</param>
    /// <returns></returns>
    private static string GetProviderManifestToken(TContext db)
    {
        var connection = db.Database.Connection;
        var token = DbProviderServices.GetProviderServices(connection).GetProviderManifestToken(connection);

        return token;
    }

    /// <summary>
    /// Gets the migration SQL generator. Currently it is <see cref="SqlServerMigrationSqlGenerator"/>.
    /// </summary>
    /// <returns></returns>
    private static MigrationSqlGenerator GetMigrationSqlGenerator()
    {
        return new SqlServerMigrationSqlGenerator();
    }

    /// <summary>
    /// Creates the operation for inserting into migration history. Operation is created for one <paramref name="migrationMetadatum"/>.
    /// </summary>
    /// <param name="migrationMetadatum">The migration metadatum.</param>
    /// <returns></returns>
    private static InsertHistoryOperation CreateInsertHistoryOperation(IMigrationMetadata migrationMetadatum)
    {
        var model = Convert.FromBase64String(migrationMetadatum.Target);

        var op = new InsertHistoryOperation(
            "__MigrationHistory",
            migrationMetadatum.Id,
            model,
            null);

        return op;
    }

    /// <summary>
    /// Generates the SQL statements for inserting migration into history table.
    /// </summary>
    /// <param name="generator">The generator.</param>
    /// <param name="op">The operation.</param>
    /// <param name="token">The token.</param>
    /// <returns></returns>
    private static IEnumerable<MigrationStatement> GenerateInsertHistoryStatements(
        MigrationSqlGenerator generator,
        InsertHistoryOperation op,
        string token)
    {
        return generator.Generate(new[] { op }, token);
    }

    /// <summary>
    /// Runs the SQL statements on database specified by <paramref name="db"/> (<see cref="DbContext.Database"/>).
    /// </summary>
    /// <param name="statements">The statements.</param>
    /// <param name="db">The db.</param>
    private static void RunSqlStatements(IEnumerable<MigrationStatement> statements, TContext db)
    {
        foreach (var statement in statements)
        {
            db.Database.ExecuteSqlCommand(statement.Sql);
        }
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="CreateDatabaseIfNotExistsAndMigrateToLatest{TContext}"/> class.
    /// </summary>
    /// <param name="migrationsAssembly">The migrations assembly.</param>
    public CreateDatabaseIfNotExistsAndMigrateToLatest(Assembly migrationsAssembly)
    {
        this.migrationsAssembly = migrationsAssembly;
    }

    protected override void Seed(TContext context)
    {
        base.Seed(context);

        // Get migration metadata for migrationAssembly
        var migrationMetadata = GetMigrationMetadata(migrationsAssembly);

        // Crate DbContext
        var db = Activator.CreateInstance<TContext>();
        // Remove newly created record in __MigrationHistory
        db.Database.ExecuteSqlCommand("DELETE FROM __MigrationHistory");

        // Get provider manifest token
        var token = GetProviderManifestToken(db);
        // Get sql generator
        var generator = GetMigrationSqlGenerator();

        foreach (var migrationMetadatum in migrationMetadata)
        {
            // Create history operation
            var op = CreateInsertHistoryOperation(migrationMetadatum);
            // Generate history insert statements
            var statements = GenerateInsertHistoryStatements(generator, op, token);
            // Run statements (SQL) over database (db)
            RunSqlStatements(statements, db);
        }
    }
}


文章来源: How to add a new code-first migration with a newly-generated database?
标签： sql-server entity-framework ef-code-first data-migration ef-migrations
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