Traverse a blob

[franzwarning]

Hi there,

 

How could I get the value of every 4 bytes of a BLOB? Additionally, how can I add an item to the end of a BLOB and store it back in the database?

 

Cheers,

George

[Xtremer360]

I'm not sure about this but curious on the purpose of it.

 

[franzwarning]

I plan on storing multiple user_id's in binary format, assuming each id is an int (4 bytes).

[franzwarning]

After doing some research, I think I can do it like this:

<?php
$result    = ibase_query("SELECT blob_value FROM table");
$data      = ibase_fetch_object($result);
$blob_data = ibase_blob_info($data->BLOB_VALUE);
$blob_hndl = ibase_blob_open($data->BLOB_VALUE);
echo         ibase_blob_get($blob_hndl, $blob_data[0]);
?>

But what is ibase? Is it like mysql_query but for BLOBS?

[kicken]

Why are you trying to store multiple user id's in a blob?  Just store one per row in a normal int column.  As for ibase, it is a different database system.  If your using mysql, you use it's functions not the ibase* functions.

 

As for working with binary data, you'd use pack and unpack but I believe your approach is incorrect.

 

[franzwarning]

I feel like that's less efficient though. I have a table called groups, where each row contains a group id, and all the member of that group in a BLOB.

[kicken]

I feel like that's less efficient though. I have a table called groups, where each row contains a group id, and all the member of that group in a BLOB.

 

No, what your proposing is less efficient and harder to use.  Databases are designed to work with tables composed of many rows.  Creating a new row per id is what it will do and handle best.

 

Think about this, what happens when you decide you want to list out all the members of a group and their details (name, email, phone, whatever you have).

 

With your method you have to:

- Select the BLOB from the table

- Use PHP to decode the ID's from the table

- Run a second query to get the details for each user

- Display the results

 

If you do one row per user ID, then all you have to do is

- Run a single query for the details

- Display the results

 

What if you decide you want to paginate the results because there are a lot of members?  Your method becomes increasingly more complicated and harder to deal with, while one-row-per-user method only has to alter the query to include a LIMIT clause.

 

[franzwarning]

Alright, you've convinced me.

 

Cheers,

Raymond