以前多对多映射都没有用过List方式，现在需要一个有序的列表结果报错 下面是代码：

class Student {
	//科目
	static hasMany = [subjects:Subject]
    List subjects
}

class Subject {
	 static mapping = {
		    table 'cto_subject'

		  }
	static belongsTo = Student
	static hasMany = [students:Student]
	String name
}

直接保持Subject里出错
errors.GrailsExceptionResolver org.springframework.dao.InvalidDataAccessResourceUsageException: could not insert: [Subject]; nested exception is org.hibernate.exception.DataException: could not insert: [Subject]
这是什么原因造成的？

从以上信息，原因我判断不出来，娃哈哈