5

我有一个使用 OOB 数据库初始化程序创建的数据库，并且我将 Code First 与 EF 4.3.1 一起使用。

我想利用 Add-Migration cmdlet 上新的“IgnoreChanges”标志，这样我就可以更改我的一些列并添加默认 SQL 值。本质上，我的一些实体有一个名为 DateLastUpdated 的列，我想将 DEFAULT 设置为 sql 表达式 GETDATE()。

我使用“add-migration InitialMigration -ignorechanges”创建了 InitialMigration，然后将以下内容添加到 Up() 和 Down()：

public override void Up()
{
    AlterColumn("CustomerLocations", "DateLastUpdated", c => c.DateTime(defaultValueSql: "GETDATE()"));
    AlterColumn("UserReportTemplates", "DateLastUpdated", c => c.DateTime(defaultValueSql: "GETDATE()"));
    AlterColumn("Chains", "DateLastUpdated", c => c.DateTime(defaultValueSql: "GETDATE()"));
}

public override void Down()
{
    AlterColumn("CustomerLocations", "DateLastUpdated", c => c.DateTime());
    AlterColumn("UserReportTemplates", "DateLastUpdated", c => c.DateTime());
    AlterColumn("Chains", "DateLastUpdated", c => c.DateTime());
}

然后我尝试运行“Update-Database -verbose”，但我看到它正在尝试在数据库上创建相同命名的默认约束，并且 SQL 抛出异常：

Applying explicit migrations: [201203221856095_InitialMigration].
Applying explicit migration: 201203221856095_InitialMigration.
ALTER TABLE [CustomerLocations] ADD CONSTRAINT DF_DateLastUpdated DEFAULT GETDATE() FOR [DateLastUpdated]
ALTER TABLE [CustomerLocations] ALTER COLUMN [DateLastUpdated] [datetime]
ALTER TABLE [UserReportTemplates] ADD CONSTRAINT DF_DateLastUpdated DEFAULT GETDATE() FOR [DateLastUpdated]
System.Data.SqlClient.SqlException (0x80131904): There is already an object named 'DF_DateLastUpdated' in the database.
Could not create constraint. See previous errors.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at System.Data.Entity.Migrations.DbMigrator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, XDocument targetModel, IEnumerable`1 operations, Boolean downgrading)
   at System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
   at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration)
   at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.RunCore()
   at System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()
There is already an object named 'DF_DateLastUpdated' in the database.
Could not create constraint. See previous errors.

看起来 EF 正在创建 DEFAULT 约束，方法是在列名后附加“DF_”，但不使用表名，以使其对表唯一。这是一个已知的错误，还是我在这里做错了什么？

4

3 回答 3

7

似乎这是一个已知的错误：msdn forums

Andrew J Peters Microsoft (MSFT) 回复：

感谢您报告此事。该问题将针对 RTM 进行修复。

一种可能的解决方法是最初使列可以为空，这将防止迁移生成额外的 DEFAULT 约束。创建列后，可以将其更改回不可为空的。

但它绝对没有在 EF 4.3.1 中修复。这是来源的相关部分：

// Type: System.Data.Entity.Migrations.Sql.SqlServerMigrationSqlGenerator
// Assembly: EntityFramework, Version=4.3.1.0, 
// Culture=neutral, PublicKeyToken=b77a5c561934e089
namespace System.Data.Entity.Migrations.Sql
{
  public class SqlServerMigrationSqlGenerator : MigrationSqlGenerator
  {
     protected virtual void Generate(AlterColumnOperation alterColumnOperation)
     {
      //...
      writer.Write("ALTER TABLE ");
      writer.Write(this.Name(alterColumnOperation.Table));
      writer.Write(" ADD CONSTRAINT DF_");
      writer.Write(column.Name);
      writer.Write(" DEFAULT ");
      //...

因此 EF 不会尝试使约束名称唯一。

您应该尝试解决方法并将其报告为错误。

编辑：我刚刚意识到上述Generate方法virtual在最坏的情况下可以继承SqlServerMigrationSqlGenerator并修复 SQL 生成并将其设置为 Configuration.cs 中的 sql 生成器：

public Configuration()
{
    AutomaticMigrationsEnabled = true;
    SetSqlGenerator("System.Data.SqlClient", 
        new MyFixedSqlServerMigrationSqlGenerator());
}

编辑2：

我认为最好的办法是在它修复回原始 SQL 之前：

public override void Up()
{
    Sql(@"ALTER TABLE [CustomerLocations] ADD CONSTRAINT 
        DF_CustomerLocations_DateLastUpdated 
        DEFAULT GETDATE() FOR [DateLastUpdated]");
    Sql(@"ALTER TABLE [CustomerLocations] ALTER COLUMN 
        [DateLastUpdated] [datetime]");
    //...
}
于 2012-03-22T22:17:23.630 回答
7

好的，根据 nemesv 的回答（已接受），这就是我现在最终解决问题的方法，直到正式发布修复程序：

internal class MyFixedSqlServerMigrationSqlGenerator : SqlServerMigrationSqlGenerator
{
    protected override void Generate(AlterColumnOperation alterColumnOperation)
    {
        if (alterColumnOperation == null)
            throw new ApplicationException("alterColumnOperation != null");

        ColumnModel column = alterColumnOperation.Column;
        if ((column.DefaultValue != null) || !string.IsNullOrWhiteSpace(column.DefaultValueSql))
        {
            using (IndentedTextWriter writer = Writer())
            {
                writer.Write("ALTER TABLE ");
                writer.Write(this.Name(alterColumnOperation.Table));
                writer.Write(" ADD CONSTRAINT DF_");
                writer.Write(alterColumnOperation.Table + "_"); //   <== THIS IS THE LINE THAT FIXES THE PROBLEM
                writer.Write(column.Name);
                writer.Write(" DEFAULT ");
                writer.Write(column.DefaultValue != null ? base.Generate(column.DefaultValue) : column.DefaultValueSql);
                writer.Write(" FOR ");
                writer.Write(this.Quote(column.Name));
                this.Statement(writer);
            }
        }
        using (IndentedTextWriter writer2 = Writer())
        {
            writer2.Write("ALTER TABLE ");
            writer2.Write(this.Name(alterColumnOperation.Table));
            writer2.Write(" ALTER COLUMN ");
            writer2.Write(this.Quote(column.Name));
            writer2.Write(" ");
            writer2.Write(this.BuildColumnType(column));
            if (column.IsNullable.HasValue && !column.IsNullable.Value)
            {
                writer2.Write(" NOT NULL");
            }
            this.Statement(writer2);
        }
    }
}


internal sealed class Configuration : DbMigrationsConfiguration<MyDbContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = true;

        SetSqlGenerator("System.Data.SqlClient", new MyFixedSqlServerMigrationSqlGenerator());
    }
    ...
}
于 2012-03-26T15:59:17.040 回答
1

此解决方案在 EF 6.1.3 中进行了测试。很可能适用于以前的版本。

您可以从 System.Data.Entity.SqlServer 命名空间实现从 SqlServerMigrationSqlGenerator 派生的自定义 sql 生成器类：

using System.Data.Entity.Migrations.Model;
using System.Data.Entity.SqlServer;

namespace System.Data.Entity.Migrations.Sql{
    internal class FixedSqlServerMigrationSqlGenerator : SqlServerMigrationSqlGenerator {
        protected override void Generate(AlterColumnOperation alterColumnOperation){
            ColumnModel column = alterColumnOperation.Column;
            var sql = String.Format(@"DECLARE @ConstraintName varchar(1000);
            DECLARE @sql varchar(1000);
            SELECT @ConstraintName = name   FROM sys.default_constraints
                WHERE parent_object_id = object_id('{0}')
                AND col_name(parent_object_id, parent_column_id) = '{1}';
            IF(@ConstraintName is NOT Null)
                BEGIN
                set @sql='ALTER TABLE {0} DROP CONSTRAINT [' + @ConstraintName+ ']';
            exec(@sql);
            END", alterColumnOperation.Table, column.Name);
                this.Statement(sql);
            base.Generate(alterColumnOperation);
            return;
        }
        protected override void Generate(DropColumnOperation dropColumnOperation){
            var sql = String.Format(@"DECLARE @SQL varchar(1000)
                SET @SQL='ALTER TABLE {0} DROP CONSTRAINT [' + (SELECT name
                    FROM sys.default_constraints
                    WHERE parent_object_id = object_id('{0}')
                    AND col_name(parent_object_id, parent_column_id) = '{1}') + ']';
            PRINT @SQL;
                EXEC(@SQL); ", dropColumnOperation.Table, dropColumnOperation.Name);

                    this.Statement(sql);
            base.Generate(dropColumnOperation);
        }
    }
}

并设置此配置：

internal sealed class Configuration : DbMigrationsConfiguration<MyDbContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = true;

        SetSqlGenerator("System.Data.SqlClient", new FixedSqlServerMigrationSqlGenerator ());
    }
    ...
}
于 2017-02-18T09:45:15.963 回答