Automatic migration was not applied because it would result in data loss

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PM> update-database -Verbose

Using StartUp project 'TopWin.Etone.Web'.

Using NuGet project 'TopWin.Etone.Domain'.

Specify the '-Verbose' flag to view the SQL statements being applied to the target database.

Target database is: 'Yunyou' (DataSource: .\sql2008, Provider: System.Data.SqlClient, Origin: Configuration).

No pending code-based migrations.

Applying automatic migration: 201307170115022_AutomaticMigration.

Automatic migration was not applied because it would result in data loss.

解决方法：提示“Automatic migration was not applied because it would result in data loss”(不能自动迁移,会导致数据丢失) ，则在Update-Database 后面加 -Force参数即可。注意，这样并不会引起数据丢失。

成功后提示：

PM> update-database -Force -Verbose

Using StartUp project 'TopWin.Etone.Web'.

Using NuGet project 'TopWin.Etone.Domain'.

Specify the '-Verbose' flag to view the SQL statements being applied to the target database.

Target database is: 'Yunyou' (DataSource: .\sql2008, Provider: System.Data.SqlClient, Origin: Configuration).

No pending code-based migrations.

Applying automatic migration: 201307170118213_AutomaticMigration.

ALTER TABLE [dbo].[Customer] ADD [CustomerName2] [nvarchar](max)

DECLARE @var0 nvarchar(128)

SELECT @var0 = name

FROM sys.default_constraints

WHERE parent_object_id = object_id(N'dbo.Customer')

AND col_name(parent_object_id, parent_column_id) = 'CustomerName1';

IF @var0 IS NOT NULL

EXECUTE('ALTER TABLE [dbo].[Customer] DROP CONSTRAINT ' + @var0)

ALTER TABLE [dbo].[Customer] DROP COLUMN [CustomerName1]

[Inserting migration history record]

Running Seed method.

PM>

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