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1. EDS:: select or create table

• Posted by K_D_R Feb 10, 2012
• 1648 views

I am having a wreck of a heck of a time trying to figure out how to create a database after db_table_list returns and a NO_TABLE error.

If the db has a table there is no problem. But if there is no table everything freezes up pronto.

This is my latest failing effort:

-- select or create table 
procedure select_or_create_table() 
    db_banner("Select Table") 
    sequence answer = {} 
    tables = {} 
    object dbtblst 
    dbtblst = db_table_list() 
      if atom(dbtblst) then 
	    if dbtblst = NO_TABLE then 
		answer = delete_trailing_white(key_gets(" ", {})) 
	    end if 
    else 
	    for i = 1 to length(dbtblst) do 
		tables = update_history(tables, sprintf("%s", {dbtblst[i]})) 
	    end for 
	    answer = delete_trailing_white(key_gets("", tables)) 
    end if 
 
    if length(answer) != 0 then 
	if db_select_table(answer)!= DB_OK then 
	    if db_create_table(answer) != DB_OK then 
		db_banner("tb") 
		any_key("Failed to create/select table! ") 
	    end if 
	end if 
	tables = update_history(tables, answer) 
    end if 
end procedure 

Any suggestions will be much appreciated.

Regards, Kenneth Rhodes

3. Re: EDS:: select or create table

• Posted by K_D_R Feb 10, 2012
• 1583 views

Key_gets was not the problem. The routine was freezing up after displaying "Select Table" on the top-line with the cursor blinking, but not accepting any keyboard input. It should have accepted the name of a table typed in by the user. The following routine works. The question now is why does the code testing dttblst for atom status and "NO_TABLE" status fail? What is the proper use of NO_TABLE?

procedure select_or_create_table() 
    db_banner("Select Table") 
    sequence answer = {} 
--  tmp = {} 
    tables = {} 
    object dbtblst 
    dbtblst = db_table_list() 
--    if atom(dbtblst) then 
--          if dbtblst = NO_TABLE then 
--              answer = delete_trailing_white(key_gets(" ", {})) 
--          end if 
--  else 
--          for i = 1 to length(dbtblst) do 
--              tables = update_history(tables, sprintf("%s", {dbtblst[i]})) 
--          end for 
--          answer = delete_trailing_white(key_gets("", tables)) 
--   
--  end if 
 
    if length(dbtblst) < 1  then 
	answer = delete_trailing_white(key_gets("",{})) 
    else 
	    for i = 1 to length(dbtblst) do 
		tables = update_history(tables, sprintf("%s", {dbtblst[i]})) 
	    end for 
	    answer = delete_trailing_white(key_gets("", tables)) 
    end if 
     
     
    if length(answer) != 0 then 
	if db_select_table(answer)!= DB_OK then 
	    if db_create_table(answer) != DB_OK then 
		db_banner("tb") 
		any_key("Failed to create/select table! ") 
	    end if 
	end if 
	tables = update_history(tables, answer) 
    end if 
end procedure 

Your assistance is appreciated.

Kenneth Rhodes

5. Re: EDS:: select or create table

• Posted by jimcbrown (admin) Feb 10, 2012
• 1473 views

I suspect that this is the key_gets() routine from ed.ex

My understanding is that this is very significant. In the former, a hot key is passed in (so pressing spacebar triggers a hot key), but in the latter, no hot keys are passed in.

db table names generally don't include spaces, however, if a space was entered then an empty string would be returned and assigned to answer.

The functional code suggests that db_table_list() is never returning an atom.

7. Re: EDS:: select or create table

• Posted by DerekParnell (admin) Feb 11, 2012
• 1453 views

if dbtblst = NO_TABLE then  

NO_TABLE is an atom. However, according to the documentation, db_table_list() returns a sequence that contains a list of table names. If this sequence is empty, there are no tables in the database.

The NO_TABLE error code is returned only by those functions that can take a table name as a parameter and the supplied table name is not known in the current database. The db_table_list() function does not accept a table name as a parameter so it does not return NO_TABLE. Also, as a database can legally contain no tables, it is never an error condition for db_table_list() to return an empty list. The NO_TABLE is an error condition so its not appropriate for db_table_list() to return that code.

9. Re: EDS:: NO_TABLE, db_table_list()

• Posted by DerekParnell (admin) Feb 11, 2012
• 1455 views

That is true. However I didn't think it would have to as an empty sequence is a list of all the tables in a database that contains no tables. I thought it was self evident as in ... 2 entries means there are 2 tables, 1 entry means that there is one table and zero entries therefore naturally means that there are no tables.

However, for Jiri's sake, I'll add this to the documentation.

8.28.3.4 NO_TABLE 
include std/eds.e 
namespace eds 
public enum NO_TABLE 
no table was found. 

The NO_TABLE value should more accurately be described as the specifically requested table was not found.

I'm not sure that I agree with this logic. Asking for a list of all tables contained within a database and receiving a list with nothing in it is simply NOT an error condition. But, for example, asking to delete a record from a specific table and that table not existing IS an error condition. I say this because the first function can complete its requested task (listing all known tables), and the second cannot complete its task.