更改列的数据类型的EF迁移 [英] EF migration for changing data type of columns

问题描述

我在我的项目如下模型：

I have a Model in my project as below:

Public Class Model {
        public int Id { get; set; }
        public long FromNo { get; set; }
        public long ToNo { get; set; }
        public string Content { get; set; }
        public long TicketNo { get; set; }
        }

迁移是如下

The migration is as below

public override void Down()
{
    AlterColumn("dbo.Received", "FromNo", c => c.Long(nullable: false));
    AlterColumn("dbo.Received", "ToNo", c => c.Long(nullable: false));
    AlterColumn("dbo.Received", "TicketNo", c => c.Long(nullable: false));
}
public override void Up()
{
    AlterColumn("dbo.Received", "FromNo", c => c.String());
    AlterColumn("dbo.Received", "ToNo", c => c.String());
    AlterColumn("dbo.Received", "TicketNo", c => c.String());
}

当我使用更新的数据库的下引发错误：

when I use Update-Database the error below is raised:

对象'DF_的输入接收的_FromN__25869641'依赖于列
'FromNo。 ALTER TABLE ALTER COLUMN FromNo失败，因为一个或多个
对象访问此列。

The object 'DF_Receiv_FromN__25869641' is dependent on column 'FromNo'. ALTER TABLE ALTER COLUMN FromNo failed because one or more objects access this column.

这表没有外键或者是什么所以还有什么问题？

This tables has no foreign key or what else so what is the problem?

推荐答案

您对您的列的默认约束。您需要先删除约束，那么改变你的栏位。

You have a default constraint on your column. You need to first drop the constraint, then alter your column.

public override void Up()
{
    Sql("ALTER TABLE dbo.Received DROP CONSTRAINT DF_Receiv_FromN__25869641");
    AlterColumn("dbo.Received", "FromNo", c => c.String());
    AlterColumn("dbo.Received", "ToNo", c => c.String());
    AlterColumn("dbo.Received", "TicketNo", c => c.String());
}

您可能不得不放弃对你的其他列的默认约束也是如此。

You will probably have to drop the default constraints on your other columns as well.

我刚看到安德烈的评论（我知道 - 很晚了），他是正确的。因此，一个更强大的方法是使用这样的：

I've just seen Andrey's comment (I know - very late) and he is correct. So a more robust approach would be to use something like:

 DECLARE @con nvarchar(128)
 SELECT @con = name
 FROM sys.default_constraints
 WHERE parent_object_id = object_id('dbo.Received')
 AND col_name(parent_object_id, parent_column_id) = 'FromNo';
 IF @con IS NOT NULL
     EXECUTE('ALTER TABLE [dbo].[Received] DROP CONSTRAINT ' + @con)

我知道这可能不利于OP但希望它有助于其他任何人遇到这个问题。

I know this probably doesn't help the OP but hopefully it helps anyone else that comes across this issue.

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