Thursday, February 2, 2012

Iteration through a table

Let's add a dump of the table contents to the "Hello, table" example, either one of them. For that, the code needs to go through every record in the table:

    elsif ($data[0] =~ /^dump$/i) {
      for (my $rhi = $tCount->begin();
          !$rhi->isNull(); $rhi = $tCount->next($rhi)) {
        print($rhi->getRow->printP(), "\n");

This code would work in either version of the example, updated either procedurally or through the input label. Here is an example of its output:

address="world" count="1"
address="table" count="2"

As you can see, the row handle works kind of like an STL iterator.  Well, not quite like an STL iterator: you can't just increase it, you have to ask the table to give you the next one.

The order of the rows in the printout is the same as the order of rows in the table's index. Which is no particular order, since it's a hashed index. As long as you stay with the same 64-bit AMD64 architecture (with LSB-first byte order), it will stay the same on different runs. But switching to a 32-bit machine or to an MSB-first byte order (such as a SPARC, if you can still find one) will change the hash calculation, and with it the resulting row order.

At the moment Triceps doesn't have an index that would keep the rows in a defined sorting order. It's not by design, it's just a result of the corner-cutting. A sorted index will be added in the future.

The some goes for the iteration order: right now the iteration can only be done in the forward order. The backward iteration is in the plans but not implemented yet.

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