EFCore-一對一配置外鍵小記2

前后兩次遇到這樣的錯誤：

The property 'xx' on entity type 'xxxx' has a temporary value. Either set a permanent value explicitly or ensure that the database is configured to generate values for this property.

多數情況下是表配置關系會出現這樣的問題。我實在配置TagItem一對一關聯TagUseCount出現的問題：

public void Configure(EntityTypeBuilder<TagItem> builder)
        {
            builder.ToTable("Tags")
                .HasKey(x => x.Id);

            builder.Property(x => x.Id).HasColumnName("TagId");
            builder.Property(x => x.TagName);

            builder.HasOne(x => x.TagUseCount)
                .WithOne(x => x.Tag)
                .HasForeignKey<Tag>(x => x.Id);
        }

以及

public void Configure(EntityTypeBuilder<TagUseCount> builder)
        {
            builder.ToTable("TagUseCount");

            builder.Property(t => t.Id)
                .HasColumnName("TagId");
            builder.Property(t => t.UseCount);
        }

以上配置有兩點錯誤，都是調試后總結出來的：

1. TagItem 關聯TagUseCount 需要指定的是關聯表的外鍵，也就是TagUseCount的Id，不能指定自己哦！
2. TagUseCount千萬別偷懶或忘記寫 builder.HasKey(x => x.Id);