Question

我一直在使用EF Code First，但这是我第一次使用EF7。

我有以下模型类，其中Venue与Show有一对多的关系：

public class Show
{
    public int Id { get; set; }
    public Venue Venue { get; set; }
    //...
}

public class Venue
{
    public int Id { get; set; }
    public string Name {get; set; }
    //...
    public List<Show> Shows { get; set; }
}

我像这样设置了DBContext：

public class NettlesContext : DbContext
{
    public DbSet<Show> Shows { get; set; }
    public DbSet<Venue> Venues { get; set; } 

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

        new ShowConfiguration(builder.Entity<Show>());
        new ImageConfiguration(builder.Entity<Image>());
    }
}

public class ShowConfiguration
{
    public ShowConfiguration(EntityTypeBuilder<Show> builder)
    {
        builder.Property(p => p.Id).IsRequired();
        builder.Property(p => p.Title).IsRequired();
    } 
}

public class VenueConfiguration
{
    public VenueConfiguration(EntityTypeBuilder<Venue> builder)
    {
        builder.Property(p => p.Id).IsRequired();
        builder.Property(p => p.Name).IsRequired();
    }
}

然后在一些启动代码中我像这样初始化数据库：

    private static void AddShows(NettlesContext db)
    {
        var shows = new List<Show>()
        {
            new Show()
            {
                Title = "Portland Country Dance Community Contra Dance",
                Venue = new Venue()
                {
                    Name = "Fulton Community Center",
                },
            },
            new Show()
            {
                Title = "Portland Roadhouse Contra Dance",
                Venue = new Venue()
                {
                    Name = "Milwaukie Community Club",
                },
            },
        };

        db.Shows.AddRange(shows);
        db.SaveChanges();
    }

显示表已正确初始化，但VenueId为空。场地表完全是空的。

发生了什么事？

Answer 1

DbSet.Add有第二个参数。

Add(TEntity entity, GraphBehavior behavior = GraphBehavior.IncludeDependents)

虽然默认为IncludeDependents（也称为儿童实体），但EF7的Add()行为并未将Venue标识为Show的孩子。在OnModelCreating中，您需要指定Venue和Show之间的关系。请参阅EF7文档中的Relationships。

示例：

modelBuilder.Entity<Venue>(entityBuilder =>
{
    entityBuilder
        .HasMany(v => v.Shows)
        .WithOne(s => s.Venue)
        .HasForeignKey(s => s.VenueId);
});

即使这样，你仍然需要在Venue的新实例上调用.Add，因为Show不是Venue的依赖（孩子）。

private static void AddShows(NettlesContext db)
{
    var fulton = new Venue()
            {
                Name = "Fulton Community Center",
            };
    var club = new Venue()
            {
                Name = "Milwaukie Community Club",
            };
    db.Venues.Add(fulton);
    db.Venues.Add(club);

    var shows = new List<Show>()
    {
        new Show()
        {
            Title = "Portland Country Dance Community Contra Dance",
            Venue = fulton,
        },
        new Show()
        {
            Title = "Portland Roadhouse Contra Dance",
            Venue = club
        },
    };
    context.Shows.AddRange(shows);
}

值得注意的是：.Add（）的这种行为一直是EF7 RC1的混乱源，其行为可能在EF7 RC2中发生变化。请参阅https://github.com/aspnet/EntityFramework/pull/4132

Answer 2

您需要更新您的模型

public class Venue
{
  public int Id { get; set; }
  public string Name {get; set; }
  //...
  public List<Show> Shows { get; set; }
 }
public class Show
{
  public int Id { get; set; }
  public int VenueId { get; set; }
  [ForeignKey("VenueId")]
  public Venue Venue { get; set; }
  //...
}

ForegnKey属性用于定义两个表之间关系的foriegn键

实体框架7 AddRange（）不添加外部实体

2 个答案: