在一对多关系中从父集合中删除子实体时删除子实体 [英] Delete child entity when removed from parent collection in one to many relationship Entity Framework

问题描述

我有以下数据库设置:

I have the following database setup:

表映射如下:

public class OrderMapping : EntityTypeConfiguration<Order>
{
    public OrderMapping()
    {
        this.ToTable("Orders", "prf");

        this.HasKey(o => o.OrderId);

        this.HasMany(o => o.OrderItems)
            .WithRequired(oi => oi.Order)
            .HasForeignKey(oi => oi.OrderId);

        this.HasRequired(o => o.Institution)
            .WithMany()
            .HasForeignKey(o => o.InstitutionId);

        this.Property(o => o.IsConfirmed)
            .IsRequired();

        this.Ignore(o => o.Id);
    }
}

public class OrderItemMapping : EntityTypeConfiguration<OrderItem>
{
    public OrderItemMapping()
    {
        this.ToTable("OrderItems", "prf");

        this.HasKey(oi => oi.OrderItemId);

        this.HasRequired(oi => oi.Order)
            .WithMany(oi => oi.OrderItems)
            .HasForeignKey(oi => oi.OrderId);

        this.HasRequired(oi => oi.Proficiency)
            .WithMany()
            .HasForeignKey(oi => oi.ProficiencyId);

        this.HasOptional(oi => oi.Enrolment)
            .WithMany()
            .HasForeignKey(oi => oi.EnrolmentId);

        this.HasMany(oi => oi.OrderItemSets)
            .WithRequired(ois => ois.OrderItem)
            .HasForeignKey(ois => ois.OrderItemId);

        this.Property(oi => oi.DateCreated);

        this.Ignore(oi => oi.Id);
    }
}

public class OrderItemSetMapping : EntityTypeConfiguration<OrderItemSet>
{
    public OrderItemSetMapping()
    {
        this.ToTable("OrderItemSets", "prf");

        this.HasKey(ois => ois.OrderItemSetId);

        this.HasRequired(ois => ois.OrderItem)
            .WithMany(ois => ois.OrderItemSets)
            .HasForeignKey(ois => ois.OrderItemId);

        this.Property(ois => ois.NumberOfSets);
        this.Property(ois => ois.Month);
    }
}

当我尝试从OrderItem的集合中删除OrderItemSet时，实体框架试图将OrderItemSet中的外键设置为null，而不是删除行，即使外键不可为空，因此抛出异常说明外键不能设置为空.

When I try to remove an OrderItemSet from the OrderItem's collection Entity Framework is trying to set the foreignkey in OrderItemSet as null instead of deleting the row even though the foreignkey is not nullable and therefore throwing an exception stating the foreignkey cannot be set to null.

this.OrderItemSets.Remove(orderItemSet);

我不知道我的映射有什么问题，让Entity Framework认为它应该将外键设置为null而不是删除行.

I don't know what is wrong with my mapping to have Entity Framework think it should set the foreignkey to null instead of deleting the row.

推荐答案

我已经按照Abbondanza的建议解决了该问题.首先，创建包含外键的实体的键(这将迫使实体框架删除子项，因为没有外键就无法存在子项):

I have resolved the issue as per Abbondanza's suggestion. First off create the key of the entity to contain the foreign key (this will force entity framework to delete the child item as it cannot exist without the foreign key):

public OrderItemSetMapping()
{
    ...

    this.HasKey(ois => new { ois.OrderItemSetId, ois.OrderItemId });

    ...
}

实体框架现在将从实体集合中删除实体，但是会删除该实体，但是由于OrderItemSetId是Identity列，这会引起另一个问题，即实体框架现在希望在向父实体添加新项目时在该列中插入一个值集合(将引发异常).通过在此列上指定DatabaseGenerationOption，将解决问题:

Entity Framework will now delete the entity if removed from the collection of the parent, however since OrderItemSetId is an Identity column this creates another issue where Entity Framework now wants to insert a value in that column when adding a new item to the parent collection (which will throw an exception). By specifying a DatabaseGenerationOption on this column the problem will be resolved:

public OrderItemSetMapping()
{
    ...

    this.Property(r => r.OrderItemSetId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

    ...
}

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