存储数据库中引用的常量的最佳方法是什么？

In my database, I have a model which has a field which should be selected from one of a list of options. As an example, consider a model which needs to store a measurement, such as 5ft or 13cm or 12.24m3. The obvious way to achieve this is to have a decimal field and then some other field to store the unit of measurement. In my database, I have a model which has a fiel