我有以下模型：
public class Employee
{
public int ID { get; set; }
public string name { get; set; }
public int LocationID { set; get; }
public virtual Location Location { set; get; }
}
public class Location {
public int ID { set; get; }
public string NAME { set; get; }
public virtual ICollection<Employee> LocationEmployees { get; set; }
}
基本上，员工属于某个地点，而且某个地点拥有大量员工。我想在名为location contact的位置模型中添加一列，该列将是一个员工ID。我尝试通过代码优先迁移添加它，但它没有产生预期的结果。
添加了列
public class Employee
{
public int ID { get; set; }
public string name { get; set; }
public int LocationID { set; get; }
public virtual Location Location { set; get; }
}
public class Location {
public int ID { set; get; }
public string NAME { set; get; }
public int EmployeeID { get; set; }
public virtual Employee Employee { get; set; }
public virtual ICollection<Employee> LocationEmployees { get; set; }
}
生成了迁移文件：
public override void Up()
{
DropForeignKey("dbo.Employees", "LocationID", "dbo.Locations");
DropIndex("dbo.Employees", new[] { "LocationID" });
RenameColumn(table: "dbo.Employees", name: "LocationID", newName: "Location_ID");
AddColumn("dbo.Locations", "EmployeeID", c => c.Int(nullable: true));
AddForeignKey("dbo.Employees", "Location_ID", "dbo.Locations", "ID");
AddForeignKey("dbo.Employees", "LocationID", "dbo.Locations", "ID", cascadeDelete: false);
AddForeignKey("dbo.Locations", "EmployeeID", "dbo.Employees", "ID", cascadeDelete: false);
CreateIndex("dbo.Employees", "Location_ID");
CreateIndex("dbo.Employees", "LocationID");
CreateIndex("dbo.Locations", "EmployeeID");
}
public override void Down()
{
DropIndex("dbo.Locations", new[] { "EmployeeID" });
DropIndex("dbo.Employees", new[] { "LocationID" });
DropIndex("dbo.Employees", new[] { "Location_ID" });
DropForeignKey("dbo.Locations", "EmployeeID", "dbo.Employees");
DropForeignKey("dbo.Employees", "LocationID", "dbo.Locations");
DropForeignKey("dbo.Employees", "Location_ID", "dbo.Locations");
DropColumn("dbo.Locations", "EmployeeID");
RenameColumn(table: "dbo.Employees", name: "Location_ID", newName: "LocationID");
CreateIndex("dbo.Employees", "LocationID");
AddForeignKey("dbo.Employees", "LocationID", "dbo.Locations", "ID", cascadeDelete: false);
}
我收到此错误：
System.Data.SqlClient.SqlException (0x80131904): Foreign key 'FK_dbo.Employees_dbo.Locations_LocationID' references invalid column 'LocationID' in referencing table 'Employees'.
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, Boolean auto)
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()
Foreign key 'FK_dbo.Employees_dbo.Locations_LocationID' references invalid column 'LocationID' in referencing table 'Employees'.
Could not create constraint. See previous errors.
我错过了什么？
答案 0 :(得分：2)
我不确切地知道为什么迁移会引发此异常，但很明显它不会创建您想要的关系。当添加三个外键而不是两个时，您可以在Up方法中看到它。 EF在此处创建三个关系，其中一个具有默认的FK名称Location_ID。
原因是EF不知道Employee.Location是否有Location.Employee或Location.LocationEmployees作为反向导航属性。
您必须使用数据注释明确定义...
public class Employee
{
//...
[InverseProperty("LocationEmployees")]
public virtual Location Location { set; get; }
}
...或使用Fluent API：
modelBuilder.Entity<Location>()
.HasMany(l => l.LocationEmployees)
.WithRequired(e => e.Location)
.HasForeignKey(e => e.LocationID);
modelBuilder.Entity<Location>()
.HasOptional(l => l.Employee)
.WithMany()
.HasForeignKey(l => l.EmployeeID);
请注意，我在第二个关系中使用了HasOptional而不是HasRequired，这意味着您还必须使Location模型中的FK可以为空：
public int? EmployeeID { get; set; }
由于没有有效的排序Employee和Location实体可以插入到数据库中，因为它们彼此相互依赖，所以不能要求这两种关系。
或者，如果符合您的业务要求，您也可以在int? LocationID Employee中与{{1}}建立其他关系。