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(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);