A primary key is a special thing in the relational model: It must be unique to each record (row) of a table.
在关系模型中主键是特殊的事物：它对于表的每个记录(行)必须是唯一的。
Active Record is an object-relational mapping (ORM) that follows a standard ORM model.
ActiveRecord是遵照了标准的or m模型的对象关系映射(object - relational mapping,ORM)。
Active Record is an object-relational mapping (ORM) that follows a standard ORM model.
ActiveRecord是遵照了标准的or m模型的对象关系映射(object - relational mapping,ORM)。
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