I can't run migration (with .net core 3.0 and entity framework)

Question

My .Net Core version is 3.0.100-preview6-012264. You can ask me why I use the preview version. The main reason is useful work with GRPC (scaffolding for this). Now I would like to use entity framework in my project. I have the following .csproj:

<Project Sdk="Microsoft.NET.Sdk.Web">

    <PropertyGroup>
        <TargetFramework>netcoreapp3.0</TargetFramework>
    </PropertyGroup>

    <ItemGroup>
        <Protobuf Include="Protos\dashboard.proto" GrpcServices="Server" Generator="MSBuild:Compile" />
        <Protobuf Include="Protos\users.proto" GrpcServices="Client" Generator="MSBuild:Compile" />
        <Protobuf Include="Protos\anal.proto" GrpcServices="Client" Generator="MSBuild:Compile" />
        <Content Include="@(Protobuf)" />
        <None Remove="@(Protobuf)" />
    </ItemGroup>

    <ItemGroup>
        <PackageReference Include="DimaRabbitLogger" Version="1.3.3" />
        <PackageReference Include="Grpc.AspNetCore.Server" Version="0.1.22-pre1" />
        <PackageReference Include="Google.Protobuf" Version="3.8.0" />
        <PackageReference Include="Grpc.Tools" Version="1.21.0" PrivateAssets="All" />
        <PackageReference Include="Grpc.Core" Version="1.21.0" />

        <PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.0.0-preview6.19304.10" />
        <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.0.0-preview6.19304.10" />
        <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.0.0-preview6.19304.10" />
        <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="3.0.0-preview5" />

        <PackageReference Include="Newtonsoft.Json" Version="12.0.2" />
        <PackageReference Include="System.Runtime.Serialization.Json" Version="4.3.0" />

    </ItemGroup>

</Project>

And couple of very simple models:

Model Application:

public class Application
{
    int ApplicationId { get; set; }

    public string PackageName { get; set; }

    public List<WorkspaceApplication> WorkspaceApplications { get; set; }

Model Workspace:

public class Workspace
{
    public int WorkspaceId { get; set; }

    public string Name { get; set; }

    public List<WorkspaceApplication> WorkspaceApplications { get; set; }

}

Class for many-to-many relationship:

public class WorkspaceApplication
{
    public int ApplicationId { get; set; }
    public Application Application { get; set; }

    public string WorkspaceId { get; set; }
    public Workspace Workspace { get; set; }
}

And my application context:

public class ApplicationContext : DbContext
{
    private readonly string _connectionString;

    public DbSet<Workspace> Workspaces { get; set; }
    public DbSet<Application> Applications { get; set; }

    public ApplicationContext(IConfiguration configuration)
    {
        _connectionString = configuration.GetConnectionString("DashboardDb");
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseNpgsql(_connectionString, b => b.MigrationsAssembly("Dashboard"));
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<WorkspaceApplication>()
            .HasKey(x => new {x.WorkspaceId, x.ApplicationId});

        modelBuilder.Entity<WorkspaceApplication>()
            .HasOne(x => x.Workspace)
            .WithMany(x => x.WorkspaceApplications)
            .HasForeignKey(x => x.WorkspaceId);

        modelBuilder.Entity<WorkspaceApplication>()
            .HasOne(x => x.Application)
            .WithMany(x => x.WorkspaceApplications)
            .HasForeignKey(x => x.ApplicationId);
    }
}

I run the following console command:

dotnet ef migrations add FirstMigration

and have this error message:

无法执行，因为找不到指定的命令或文件。可能的原因： * 您输入的内置 dotnet 有误。* 您计划运行 .NET Core，但 dotnet-ef 不存在。* 您想运行全局工具，但在 PATH 中指定的 PATH 找不到具有此名称的带有 dotnet 前缀的可执行文件。

这适用于 .Net Core 2.2。问题出在哪儿？

Answer 1

从 3.0 开始，dotnet ef它不再是 .NET SDK 的一部分。

旧行为

在 3.0 之前，dotnet ef 工具包含在 .NET Core SDK 中，可随时从任何项目的命令行使用，无需额外步骤。

新行为

从 3.0 开始，.NET SDK 不包含 dotnet ef 工具，因此在使用它之前，您必须将其显式安装为本地或全局工具。

要安装它，您可以运行以下命令：

dotnet tool install --global dotnet-ef --version 3.0.0-*

然后你应该能够运行正常的 ef-core 命令，比如 dotnet ef migrations add ...

不要忘记在PATH操作系统的变量中添加 dotnet 工具的路径。例如，如果您使用 linux ubuntu 和 zsh 作为 shell，则必须在.zshrc文件中添加以下内容：

export PATH=$PATH:$HOME/.dotnet/tools