EF CORE 外键关联小记

前后两次遇到这样的错误：

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.

多数情况下是表配置关系会出现这样的问题。我实在配置TagItem一对一关联TagUseCount出现的问题：

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

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

以上配置有两点错误，都是调试后总结出来的：

TagItem 关联TagUseCount 需要指定的是关联表的外键，也就是TagUseCount的Id，不能指定自己哦！
TagUseCount千万别偷懒或忘记写 builder.HasKey(x => x.Id);