Friday, October 12, 2012

Adding Moodle 1.9 Block Restore to Moodle 2.3 - Part 3

This is part three of my series on writing the Moodle 1.9 to 2.3 block restore conversion code for Moodle core.

Up to this point, all I've really done is figured out some of the basic operation of the Moodle 1.9 restore converter, and verified my findings using some new test code. This exploration has shown me that the heavy lifting I need to do is convert the data format from a 1.9 backup file to the data format used by Moodle 2. Essentially, I need to look at what data was stored in a 1.9 backup, compare it to what is in a 2.x format and plan for that transformation.

Looking at the backup XML first, in 1.9 I see:
In 2.3, I see:
<block id="10" contextid="278" version="2012061700">
    <block_position id="1">
I need to analyze this data and structures and determine how I migrate the old to the new.

The easy ones (I believe) should be able to transfer "as is":
  • ID => id
  • NAME => blockname
  • CONFIGDATA => configdata
The others will require some transformation processing. I'll look at each one.

contextid - This would be the context instance id value of the block on the system it was backed up from. Since this is not kept in 1.9 backups, I'll need to create one. This is a common problem with all 1.9 converters, so there should be examples I can borrow.

version - This would be the version string of the block when it was backed up. This is not in the 1.9 backup information. I'll have to find what I can use in its place, possibly leaving it blank.

parentcontextid - This is likely the context instance id of the context the block is installed on. This is not part of the 1.9 backup, but the page id (PAGEID) is. I may be able to use it, since what is probably most important is consistency for any block on that page.

showinsubcontexts - This is a new feature of blocks previously not available in Moodle 1.9. I should be able to just default this to zero.

pagetypepattern - This is a new setting for blocks in M2. This looks to be similar to PAGETYPE, but is a setting that impacts what pages it will displayed on. This will require a bit of investigation.

subpagepattern - This is a new feature of blocks previously not available in Moodle 1.9. It looks like I should be able to default this to $@NULL@$.

defaultregion, defaultweight - These are other new settings for M2 and can probably be set to default values.

block_positions - The block positions structure's elements pagetype, visible, region and weight will be based on the PAGETYPE, VISIBLE, POSITION, and WEIGHT elements but will require some transforms. The other elements in there, id, contextid and subpage will require more investigation.

So, I have some idea of what I need to do with the block data. Now I need to plan for where that will happen (so I can play with code and see what I need to do).

There is already a moodle1_block_handler class defined in the "handlerlib.php" file. This has been created primarily to be extended by any block that needs it. Recall from my previous post, that all handlers get registered for use in the moodle1_handlers_factory::get_handlers() function. In this function, any block that provides a moodle1_block_handler instance also gets registered. I need to also register a handler for all blocks to do the generic work associated with every block.I'm thinking, this should all be part of the moodle1_block_handler class, such that every block is managed by functions in this class. And that class should be responsible for calling any specific block backup code provided by those blocks. I'm going to try designing this approach to see if it makes sense.

After I've bounced this idea of some of the developers in the tracker, I'll come back to this.

1 comment:

  1. Based on my experience with writing converters, let me recommend to always look at the upgrade code. Even presumptions that seem to be "obvious" (like letting configdata as-is) may be wrong once you look into to upgrade code (I'm not saying this is the case, just took it as an example).

    In other words, new/modified data in MBZ had to be introduced in some upgrade step. We need to make sure we replay all relevant upgrade steps correctly. As highlighted in the docs, when writing a converter, you should refer to 1) original 1.9 backup code, 2) new 2.x backup code and 3) the upgrade code.