Question

我使用Entity Framework Core3。我创建了新的Present文件

Present.cs

public class Present
{
    [Key]
    public string PresentedId { get; set; }
    public string ReagentId { get; set; }
    [Column(TypeName ="smalldatetime")]
    public DateTime Date { get; set; }
    public bool Paid { get; set; }
    public double ShareAmount { get; set; }
    [ForeignKey("ReagentId")]
    public virtual AppUser Reagent { get; set; }
    [ForeignKey("PresentedId")]
    public virtual AppUser Presented { get; set; }
}

我的DBContext

public class AppDbContext : IdentityDbContext<AppUser, IdentityRole, string>
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
    {

    }
    ///...
    public virtual DbSet<Present> Presents { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        ///...
        builder.Entity<Present>()
            .Property(e => e.Date)
            .HasDefaultValueSql("getutcdate()");

        builder.Entity<AppUser>()
            .HasOne(e => e.Reagent)
            .WithOne(e => e.Presented);

        builder.Entity<AppUser>()
       .HasMany(e => e.Presents)
       .WithOne(e => e.Reagent)
       .HasForeignKey(e => e.ReagentId)
       .OnDelete(DeleteBehavior.NoAction);
    }
}

我添加了迁移

dotnet ef migrations add addedPresent ///this was successfull,and was not empty for first time
dotnet ef database update             /// this was with error

但是当我想更新数据库时，我遇到了一个错误，应该删除Cascad。在数据库中，它没有创建新表（Present），也没有在Migrations table中添加新行，因此，我删除了上一次迁移我将OnDelete(DeleteBehavior.Cascade);更改为OnDelete(DeleteBehavior.NoAction); 然后我添加了新的Migrations。但是我的问题是它将创建一个空的Migrations文件，我不知道如何解决这个问题？

public partial class addpresent : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
    }
    protected override void Down(MigrationBuilder migrationBuilder)
    {
    }
}

修改

我使用以下命令删除迁移

dotnet ef migrations remove --force

并执行错误，但删除了迁移文件（addPresent.cs）

dotnet ef迁移删除--force 信息：Microsoft.EntityFrameworkCore.Infrastructure [10403] 实体框架核心3.0.0使用提供程序'Microsoft.EntityFrameworkCore.SqlServer'初始化了'AppDbContext'，选项如下：执行DbCommand [Parameters = []，CommandType ='Text'，CommandTimeout = '30'] SELECT OBJECT_ID（N'[__ EFMigrationsHistory]'）; 信息：Microsoft.EntityFrameworkCore.Database.Command [20100] 执行DbCommand [Parameters = []，CommandType ='Text'，CommandTimeout = '30'] SELECT OBJECT_ID（N'[__ EFMigrationsHistory]'）; 执行DbCommand [Parameters = []，CommandType ='Text'，CommandTimeout = '30'] 选择[MigrationId]，[ProductVersion] 来自[__EFMigrationsHistory] ORDER BY [MigrationId]; 信息：Microsoft.EntityFrameworkCore.Database.Command [20100] 执行DbCommand [Parameters = []，CommandType ='Text'，CommandTimeout = '30'] 选择[MigrationId]，[ProductVersion] 来自[__EFMigrationsHistory] ORDER BY [MigrationId]; 正在删除迁移'20191124071753_addPresent'。 System.NullReferenceException：对象引用未设置为对象的实例。在Microsoft.EntityFrameworkCore.Design.Internal.CSharpHelper.Literal（字符串值）在Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GeneratePropertyAnnotations（IProperty属性，IndentedStringBuilder stringBuilder）中在Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateProperty（String builderName，IProperty属性，IndentedStringBuilder stringBuilder）在Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateProperties（String builderName，IEnumerable 1 properties, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityType(String builderName, IEntityType entityType, IndentedStringBuilder stringBuilder) at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityTypes(String builderName, IReadOnlyList 1 entityTypes，IndentedStringBuilder stringBuilder）中在Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.Generate（字符串builderName，IModel模型，IndentedStringBuilder stringBuilder）在Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationsGenerator.GenerateSnapshot（String modelSnapshotNamespace，Type contextType，String modelSnapshotName，IModel模型）在Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.RemoveMigration（String projectDir，String rootNamespace，Boolean force，String语言）在Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.RemoveMigration（String contextType，Boolean force）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.RemoveMigrationImpl（String contextType，Boolean force）处在Microsoft.EntityFrameworkCore.Design.OperationExecutor.RemoveMigration。<> c__DisplayClass0_0。<。ctor> b__0（）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase。<> c__DisplayClass3_0`1.b__0（）在Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute（Action操作）对象引用未设置为对象的实例。

我添加了“新迁移”，但它仍为空文件

dotnet ef migrations add addPresent

编辑2：

现在，我添加了一个表Conversation（用于测试），并且添加了迁移功能，并且可以正常运行

dotnet ef database update

它向数据库添加了表。但是数据库中没有Present表。我不知道它如何检测到我添加了Conversation却没有检测到我添加了Present。现在该怎么办？

为什么添加迁移会创建空的迁移文件？

0 个答案: