为 entity framework 创建与其他记录有关系的记录：ASP.NET Core 6 Minimal API (SQL / Postgres)

Question

我有两个 table，Participant 和 Meeting，在一个 ASP.NET Core 6 minimal API 项目中设置如下：

record Participant(int id)
{
    public string name { get; set; } = default!;
    public string title { get; set; } = default!;
}

record Meeting(int id)
{
    public string subject { get; set; } = default!;
    public string organizer { get; set; } = default!;
    public DateTime starttime { get; set; } = default!;
    public DateTime endtime { get; set; } = default!;
}

class MyDb: DbContext 
{
    public MyDb(DbContextOptions<MyDb> options): base(options) 
    {
    }

    public DbSet<Participant> Participants => Set<Participant>();

    public DbSet<Meeting> Meetings => Set<Meeting>();
}

现在我需要创建一个组合 table/记录来连接这两个 tables/记录

在 SQL 中就是这样 table

CREATE TABLE meetings_participants
(
    meeting_id int NOT NULL,
    participant_id int NOT NULL,
    PRIMARY KEY (meeting_id, participant_id),
    CONSTRAINT fk_meeting_id 
        FOREIGN KEY (meeting_id) REFERENCES meetings(id),
    CONSTRAINT fk_participant_id 
        FOREIGN KEY (participant_id) REFERENCES participants(id)
);

但是我如何在 EF 中将它写为带有外键的记录？

Answer 1

您可以像这样创建一个 MeetingParticipant class：

public class MeetingParticipant
{
    public int  ParticipantID { get; set; }
    [ForeignKey("ParticipantID")]
    public virtual Participant Participant { get; set; }
    public int MeetingID { get; set; }
    [ForeignKey("MeetingID")]
    public virtual Meeting Meeting { get; set; }
}

并更新参与者和会议 class 如下：

public record Participant(int id)
{
    public string name { get; set; } = default!;
    public string title { get; set; } = default!;

    public List<MeetingParticipant> MeetingParticipant { get; set; }
}

public record Meeting(int id)
{
    public string subject { get; set; } = default!;
    public string organizer { get; set; } = default!;
    public DateTime starttime { get; set; } = default!;
    public DateTime endtime { get; set; } = default!;
    public List<MeetingParticipant> MeetingParticipant { get; set; }
}

然后，更新 ApplicationDbContext（您可以将其更改为您的），如下所示：

public class ApplicationDbContext : IdentityDbContext
{ 
    public DbSet<Participant> Participants => Set<Participant>();

    public DbSet<Meeting> Meetings => Set<Meeting>();

    public DbSet<MeetingParticipant> MeetingParticipant { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    { 
        base.OnModelCreating(modelBuilder);
        //set the primary key
        modelBuilder.Entity<MeetingParticipant> ().HasKey(mp=> new { mp.MeetingID, mp.ParticipantID}); 
    }

然后，使用 EF 迁移命令启用迁移，如下所示（如果使用 Visual Studio）：

Add-Migration AddMeetingParticipant
Update-Database

然后，它将在Participant和Meeting table之间配置many-to-many，MeetingParticipant table用于存储关系。

更多关于EF核心关系的详细信息，请参考以下文章：

Many-to-many Relationships

Configure Many-to-Many Relationships in Entity Framework Core

为 entity framework 创建与其他记录有关系的记录：ASP.NET Core 6 Minimal API (SQL / Postgres)

Creating record for entity framework with relationships to other records : ASP.NET Core 6 Minimal API (SQL / Postgres)

c#

asp.net-web-api

entity-framework-6

asp.net-core

minimal-apis