使用 Entity Framework Core 在具有多对多关系的数据透视表中插入新记录答案

【问题标题】：Insert new record in pivot table with many to many relationship using Entity Framework Core使用 Entity Framework Core 在具有多对多关系的数据透视表中插入新记录
【发布时间】：2018-12-31 15:50:01
【问题描述】：

我正在使用 ASP.NET Core MVC 构建应用程序。我正在尝试插入具有多对多关系的新记录。我有 3 张桌子 Repairs、Parts 和 RepairParts。

如何将RepairId 和PartId 插入RepairParts 表中？ EF Core 是否为此提供了一些东西？我搜索了文档，但没有提及如何执行此操作。

Entity Framework 会自动执行此操作吗？（插入数据透视表）还是我需要手动操作？举个例子会有所帮助。

修复类：

public class Repair
{
    [Key]
    public int RepairId { get; set; }

    public int VehicleId { get; set; }
    public string Notes { get; set; }
    public string Mileage { get; set; }
    public DateTime RepairDate { get; set; }
    public string uuid { get; set; }

    [ForeignKey("VehicleId")]
    public Vehicle Vehicle { get; set; }

    public virtual ICollection<RepairParts> RepairParts { get; set; }
}

部分类：

public class Part
{
    public int PartId { get; set; }
    public int Code { get; set; }
    public string PartCode { get; set; }
    public string Type { get; set; }
    public string Name { get; set; }
    public string Descr { get; set; }
    public string Manufacturer { get; set; }
    public string uuid { get; set; }

    public virtual ICollection<RepairParts> RepairParts { get; set; }
}

RepairPart类：

public class RepairParts
{
    public int RepairId { get; set; }
    public Repair Repair { get; set; }

    public int PartId { get; set; }
    public Part Part { get; set; }

    public decimal price { get; set; }
}

DbContext 类：

public class ApplicationDbContext : IdentityDbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public DbSet<Customer> Customers { get; set; }
    public DbSet<TaxOffice> TaxOffices { get; set; }
    public DbSet<Vehicle> Vehicles { get; set; }
    public DbSet<Part> Parts { get; set; }
    public DbSet<Repair> Repairs { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<Customer>()
              .HasMany(v => v.Vehicles)
              .WithOne(b => b.Customer);

        builder.Entity<Vehicle>()
             .HasOne(c => c.Customer)
             .WithMany(b => b.Vehicles);

        builder.Entity<Vehicle>()
              .HasMany(v => v.Repairs)
              .WithOne(c => c.Vehicle);

        builder.Entity<RepairParts>()
            .HasKey(t => new { t.RepairId, t.PartId });

        builder.Entity<RepairParts>()
            .HasOne(r => r.Repair)
            .WithMany(t => t.RepairParts)
            .HasForeignKey(f => f.RepairId);

        builder.Entity<RepairParts>()
            .HasOne(r => r.Part)
            .WithMany(p => p.RepairParts)
            .HasForeignKey(f => f.PartId);
    }
}

【问题讨论】：

Entity Framework 会自动执行此操作吗？ 不，这是简短且唯一的答案。

标签： c# entity-framework asp.net-core many-to-many

【解决方案1】：

这里有两个选择：

插入RepairPartspublic virtual ICollection<RepairParts> RepairParts { get; set; }

var repaire = new Repair { uuid = "R3" };
var part = new Part { Code = 3 };
var reparePart = new RepairParts { Repair = repaire, Part = part };
repaire.RepairParts = new List<RepairParts>()
{
    reparePart
};
_context.Add(repaire);
_context.SaveChanges();

由_context.Add(reparePart1); 明确插入RepairParts

var repaire1 = new Repair { uuid = "RR1" };
var part1 = new Part { Code = 4 };
var reparePart1 = new RepairParts { Repair = repaire1, Part = part1 };
_context.Add(repaire1);
_context.Add(part1);
_context.Add(reparePart1);
_context.SaveChanges();

【讨论】：