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TechTip: BLOBs Keep PDF, XLS, and Other Reports Safe in DB2, Part 1

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Ever had a user asking for a report you couldn't generate again because it was a "snapshot" of your database at a certain time? Here's how to fix that!

 

This TechTip will tell you all you need to know about the BLOB. No, we're not talking about the 1958 Steve McQueen movie or the Marvel villain. We're going to revisit a fairly old concept, with a new twist: the Binary Large OBject. I'll explain how and why you can use it in the context of iSeries-generated PDFs and charts. Read on to find out more.

 

A BLOB is, basically, a way to store a non-native object on a DB2 database. By non-native object, I mean a file, such as a PDF, a spreadsheet, or a web page. This can be especially useful when your application generates reports in these (or other) formats and you need to retrieve them quickly, without having to produce the report all over again. In fact, if your report is a "snapshot" of a certain moment (like the end of the month or quarter, for instance), it might be hard to produce the exact same report.

 

As you might have guessed by now, the DB2 implementation of the BLOB concept consists of a kind of column on a database table. I say "kind of" because you cannot actually query this column; all you'll see is a pointer reference. In order to access the content, you need to extract it to the IFS.

 

Let's start by creating a table with some information to help us identify what's inside each BLOB:

 

CREATE TABLE RPTARCHIVE/REPORTS

 

(RPT_ID DECIMAL (7 , 0)

 

, RPT_TYPE CHAR (10 )

 

, RPT_TIME TIMESTAMP

 

, RPT_RMK CHAR (200 )

 

, RPT_FILE1 BLOB (500K )

 

, CONSTRAINT PK_RPT_ID UNIQUE (RPT_ID))

 

Rpt_Id is the unique identifier of the stored file, and Rpt_Type and Rpt_Rmk (short for remark) will help you identify the content without having to extract it to the IFS. Finally, I've created the BLOB itself (Rpt_File1) with 500K. This is something you need to handle with care, because the BLOB size is not dynamic or dependant on the content size. In other words, each line of this table will occupy a little of 500K of disk space, regardless of the file size contained within the BLOB. Another detail that might be important for the development management of this table is that it cannot be created with a DDS. Currently, there's no way to create a BLOB-type column using DDS keywords.

 

Now that we have our "report archive," it's time to store something on it. In order to do that, you need to use a special data structure composed of the following fields:

 

  • File Name Length (10u 0)The size of the complete file and path name in characters
  • Data Length (10u 0)The size of the file (an optional parameter)
  • File Option (10u 0)The operation you want to execute (I'll explain this further on)
  • File Name (255A )The complete path and file name

 

The Blob_In sample program stores the PDF file /Reports/Test.PDF into the REPORTS table:

 

     D Rpt_ID         S             7 0 Inz(*Zeros)

 

     D Rpt_Type       S             10   Inz(*Blanks)

 

     D Rpt_Rmk         S           255   Inz(*Blanks)

 

 

     D File_In         s                   SQLTYPE(BLOB_FILE)

 

 

     * The SQLTYPE(BLOB_FILE) definition will be converted by the compiler

 

     * into the following data structure:

 

     D*File_In         DS

 

     D*File_In_NL                   10U 0

 

     D*File_In_DL                   10U 0

 

     D*File_In_FO                   10U 0

 

     D*File_In_NAME                 255A

 

 

 

     // Store an object into the blob table

 

     /FREE

 

       Rpt_ID = 1;

 

       Rpt_Type = 'PDF';

 

       Rpt_Rmk = 'Just a PDF test report';

 

       File_In_FO   = SQFRD;

 

       File_In_NAME = '/Reports/Test.PDF';

 

       File_In_NL   = %len(%trimr(File_In_NAME));

 

 

       EXEC SQL   Insert Into RptArchive/Reports

 

                         Values (:Rpt_ID, :Rpt_Type, NOW(),

 

                                :Rpt_Rmk , :File_In);

 

 

 

       *InLr = *On;

 

     /END-FREE

 

Here, I'm passing all the relevant information into the special data structure and executing a simple INSERT statement. Note that I didn't actually define the File_In data structure; I defined a SQLTYPE(BLOB_File) field, which the compiler converts into the special data structure I mentioned above.

 

If you query the REPORTS table, you'll see the newly inserted record. As I mentioned before, you can't actually see the file inside the BLOB; you will see a pointer instead. That's why I added the Rpt_Type and Rpt_Remark columns to the table.

 

Now, let's retrieve the file from the archive, with the BLOB_OUT sample program: 

 

     D Rpt_ID         S             7 0 Inz(*Zeros)

 

 

     D File_Out       s                   SQLTYPE(BLOB_FILE)

 

 

     * The SQLTYPE(BLOB_FILE) definition will be converted by the compiler

 

     * into the following data structure:

 

     D*File_Out       DS

 

     D*File_Out_NL                   10U 0

 

     D*File_Out_DL                   10U 0

 

     D*File_Out_FO                   10U 0

 

     D*File_Out_NAME               255A

 

 

 

     // Retrieve an object from the blob table

 

 

     /FREE

 

       Rpt_ID = 1;

 

       File_Out_FO   = SQFOVR;

 

       File_Out_NAME = '/Reports/Test_Out.PDF';

 

       File_Out_NL   = %Len(%TrimR(File_Out_NAME));

 

 

       EXEC SQL   Select Rpt_File1

 

                   Into :File_Out

 

                   From RptArchive/Reports

 

                   Where Rpt_Id = :Rpt_Id;

 

 

       *InLr = *On;

 

 

     /END-FREE

 

Again, I'm passing all the relevant information to the special data structure in order to retrieve the file with a SELECT statement. Other than the SQL statement used, the big difference between the two programs is the file option I used (…_FO field of the special data structure). In the first program, it was SQFRD, which tells the program I'm using the file in "read mode"; in the second program, I wanted to write the file to the IFS, overwriting it if it existed. For that I chose SQFOVR. Here's the complete list of file options available:

 

  • SQFRDOpen IFS file for reading only
  • SQFCRTCreate IFS file if it doesn't exist, and open for writing
  • SQFOVRCreate IFS file if it doesn't exist, overwrite it if it does exist, and open for writing
  • SQFAPPAppend data to the end of an existing IFS file

 

In the second part of this TechTip, I'll walk you through the creation of simplified store/retrieve procedures that can be used in both RPG and SQL!

 

 

Rafael Victoria-Pereira

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.


MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale

SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

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