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+---- Thread: Variable length string database, using an index file (/showthread.php?tid=142)
Variable length string database, using an index file - SMcNeill - 04-23-2022
Code: (Select All)
'Random length string database creation.
'This demo will utilize two different files to manage our database.
'the first one will be the data, and the second will be our index to the data
TYPE RecordType
Name AS STRING
Age AS _BYTE
Sex AS STRING
Phone AS STRING
END TYPE
TYPE IndexType
StartPosition AS LONG
LengthName AS LONG 'track how long the name is
LengthSex AS LONG 'track how long the sex is
LengthPhone AS LONG 'track how long the phone is
END TYPE
DEFLNG A-Z
DIM SHARED Record AS RecordType, Index AS IndexType
DIM SHARED RecordNumber, RecordCount
OPEN "Demo.dba" FOR BINARY AS #1 'the demo database
OPEN "Demo.ndx" FOR BINARY AS #2 'the demo index
RecordCount = LOF(2) \ LEN(Index)
DO
choice = ShowOptions
SELECT CASE choice
CASE 1: AddRecord
CASE 2:
CASE 3:
CASE 4: RecordNumber = RecordNumber - 1: IF RecordNumber < 1 THEN RecordNumber = RecordCount
CASE 5: RecordNumber = RecordNumber + 1: IF RecordNumber > RecordCount THEN RecordNumber = 1
CASE 6: SYSTEM
END SELECT
LOOP
SUB ShowMainInfo
CLS
IF RecordNumber > 0 THEN 'Get the current record and display it
GET #2, (RecordNumber - 1) * LEN(Index) + 1, Index
Record.Name = SPACE$(Index.LengthName)
Record.Sex = SPACE$(Index.LengthSex)
Record.Phone = SPACE$(Index.LengthPhone)
GET #1, Index.StartPosition, Record.Name
GET #1, , Record.Age
GET #1, , Record.Sex
GET #1, , Record.Phone
ELSE
Record.Name = ""
Record.Age = 0
Record.Sex = ""
Record.Phone = ""
END IF
PRINT "Steve's Variable Length Database Demo"
PRINT
PRINT "Record RECORD "; RecordNumber; " of "; RecordCount
PRINT "Name : "; Record.Name
PRINT "Age : "; Record.Age
PRINT "Sex : "; Record.Sex
PRINT "Phone: "; Record.Phone
PRINT
PRINT
END SUB
SUB AddRecord
RecordNumber = 0 'Display a blank record
ShowMainInfo
RecordCount = RecordCount + 1 'increase our total count of records
RecordNumber = RecordCount 'And set our current record to the new record count value
PRINT "ENTER Name : "
PRINT "ENTER Age : "
PRINT "ENTER Sex : "
PRINT "ENTER Phone: "
LOCATE 10, 14: INPUT ; ""; Record.Name
LOCATE 11, 14: INPUT ; ""; Record.Age
LOCATE 12, 14: INPUT ; ""; Record.Sex
LOCATE 13, 14: INPUT ; ""; Record.Phone
filesize = LEN(Record.Name) + LEN(Record.Age) + LEN(Record.Sex) + LEN(Record.Phone)
Index.StartPosition = LOF(1) + 1
Index.LengthName = LEN(Record.Name)
Index.LengthSex = LEN(Record.Sex)
Index.LengthPhone = LEN(Record.Phone)
PUT #2, (RecordCount - 1) * LEN(Index) + 1, Index
t$ = Record.Name: PUT #1, LOF(1) + 1, t$ 'We must use a temp string, as we can't put a variable length string type to a file
PUT #1, , Record.Age
t$ = Record.Sex: PUT #1, , t$
t$ = Record.Phone: PUT #1, , t$
END SUB
FUNCTION ShowOptions
ShowMainInfo
PRINT "1) Add Record"
PRINT "2) Delete Record Record (Not Implemented Yet)"
PRINT "3) Edit Record Record (Not Implemented Yet)"
PRINT "4) Previous Record"
PRINT "5) Next Record"
PRINT "6) Quit"
PRINT
PRINT
DO
i$ = INPUT$(1)
SELECT CASE i$
CASE "1" TO "6": ShowOptions = VAL(i$): EXIT FUNCTION
END SELECT
LOOP
END FUNCTIONFolks have recently been talking about how to make databases with BINARY vs RANDOM access, and somebody brought up how they'd manage variable length strings with a database, using line terminations and parsing... (I think it might have been bplus who mentioned that method.)
Here's how I generally work with handling variable length strings with a database.
For each variable length database, I usually use two databases -- one for the data, and one for an index to the data, which is what I'm doing with the above. (Though sometimes, I'll pack both files into one database, with the index being a set positional header, and the data coming after that header -- but I thought I'd show the simplest form of the process first.)
Now, before I let the demo get too complicated that it might turn folks off from looking at it, I'm just going to post the bare bones of the process first. The code above basically doesn't do anything except allow us to ADD RECORDS, and browse those records sequentially -- but it does show how we'd GET/PUT our information, and track where all that information is while on a disk for us.
RecordNumber is the current record that we're looking at
RecordCount is the total number of records which our database contains.
"Demo.dba" is the demo database
"Demo.ndx" is the demo index
In AddRecord, you can see where we get the information from the user and how we put the proper information onto the drive for us, so we can access it later, and in ShowMainInfo, you can see the process by which we get that information back for us.
Honestly, I don't think there's anything very complicated about what we're doing here, so I really don't know what I need to comment on, or what questions someone might have about the process. If anyone has any specific questions, feel free to ask, and I'll happily answer them, but the process is really very simple:
One file is the user's data, the other file tracks each record's position and lengths inside that file, so we only retrieve and work with what we want, when we want it.
A simple database is included below, but you can freely ignore it if you want. Just run the code above and add your own records and browse them all you want.
