全局禁用 EF Core 2 上的级联删除

Question

我需要了解在EF Core 2 中全局禁用级联删除的方法。任何帮助都可以得到。

在 EF 6.x 中，我们使用以下代码禁用 OneToMany 和 ManyToMany 的级联删除：

builder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
builder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();

Answer 1

不幸的是，目前的 EF Core（目前是最新的 v2.0）没有公开一种全局控制约定的好方法。

默认的 EF Core 2.0 约定是使用 DeleteBehavior.Cascade 表示必需关系，使用 DeleteBehavior.ClientSetNull 表示可选关系。我可以建议的解决方法是在OnModelCreating 覆盖末尾的典型元数据模型循环。在这种情况下，定位所有已经发现的关系并相应地修改它们：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // ...

    var cascadeFKs = modelBuilder.Model.GetEntityTypes()
        .SelectMany(t => t.GetForeignKeys())
        .Where(fk => !fk.IsOwnership && fk.DeleteBehavior == DeleteBehavior.Cascade);

    foreach (var fk in cascadeFKs)
        fk.DeleteBehavior = DeleteBehavior.Restrict;

    base.OnModelCreating(modelBuilder);
}

Answer 2

constraints: table =>
                {
                    table.PrimaryKey("PK_ComandaPlato", x => x.ComandaPlatoId);
                    table.ForeignKey(
                        name: "FK_ComandaPlato_Comanda_ComandaId",
                        column: x => x.ComandaId,
                        principalTable: "Comanda",
                        principalColumn: "ComandaId",
                        onDelete: ReferentialAction.Cascade);//default: cascade on
                    table.ForeignKey(
                        name: "FK_ComandaPlato_Plato_PlatoId",
                        column: x => x.PlatoId,
                        principalTable: "Plato",
                        principalColumn: "PlatoId",
                        onDelete: ReferentialAction.NoAction);//turn off cascade,"by hand"
                });
//comments: modifing the auto-generated migration, "harcode by hand" this attibute, as view bellow: change "Cascade" to "NoAction" (as view 1st and 2st examples)

Answer 3

可能会有所帮助：

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
ChangeTracker.CascadeDeleteTiming = ChangeTracking.CascadeTiming.Never;
ChangeTracker.DeleteOrphansTiming = ChangeTracking.CascadeTiming.Never;
}