erlang mnesia create table error

Question

I am trying to create mnesia table from Erlang shell. I got error and the same error for the below syntax copied from mnesia help documents.

mnesia:create_table(employee,
    [{attributes, record_info(fields, employee)}]).

got the error

record employee undefined

tried various combinations, getting same error. mnesia already started.

rvirding rvirding · Accepted Answer · 2014-04-22T08:45:30

You need to have the record employee defined before you can do record_info on it. In the shell use can use rr(FileName). command which will find all the record definitions in the file and remember them. In a module you would either define the record directly in the module or include a file which contains the record definition.

The reason for having to do this special handling in the shell is that records are purely a compile-time feature so a record definition doesn't really "exist" anywhere.

EDIT: If you want to define the record directly in shell then you can't use the standard -record(...). syntax. That is only valid in modules. The shell sees that as a call to the record/2 function. You need to use the rd shell command. It your case it would become:

3> rd(employee, {emp_no, name, salary, sex, phone, room_no}).
employee
4> record_info(fields, employee).
[emp_no,name,salary,sex,phone,romm_no]
5>

Then record_info works. If you already have the record definitions in a file then use the shell rr(File). command instead as it is easier. I think.

erlang mnesia create table error

2 Answers