| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Chutney v5; Weird Componentized Virus; Interesting Argentinian Author - Antonio Di Benedetto; Useful Thread on MetaPhysics; RAND on fighting online anarchy (2001); Now Is Cat Soft LLC's Chance To Save Up To 32% On Mail; NSA Hacked; Call Center Services for Cat Soft LLC; Very Good LRB Article on Brexit; Nussbaum on Anger; Credit Card Processing for Cat Soft LLC; Discover new movies on demand in our online cinema; Tasting; Credit Card Processing for Cat Soft LLC; Apple + Kiwi Jam; Hit Me; Increase Efficiency with GPS Vehicle Tracking for Cat Soft LLC; Sudoku - CSP + Chaos; Recycling Electronics In Santiago; Vector Displays in OpenGL; Call Center Services for Cat Soft LLC; And Anti-Aliased; OpenGL - Render via Intermediate Texture; And Garmin Connect; Using Garmin Forerunner 230 With Linux; Payroll Service Quotes for Cat Soft LLC; (Beating Dead Horse) StackOverflow; Current State of Justice in China; Now Is Cat Soft LLC's Chance To Save Up To 32% On Mail; Axiom of Determinacy; Ewww; Fee Chaos Book; Course on Differential Geometry; Increase Efficiency with GPS Vehicle Tracking for Cat Soft LLC; Okay, but...; Sparse Matrices, Deep Learning; Sounds Bad; Applebaum Rape; Tomato Chutney v4; Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command

© 2006-2015 Andrew Cooke (site) / post authors (content).

Using Scala with Empire DB

From: andrew cooke <andrew@...>

Date: Wed, 7 Oct 2009 23:28:18 -0400

Bringing together two different language paradigms doesn't seem to be
easy.  For example, merging OO and functional programming seems to
have taken quite some time.  I am not sure where the problem lies -
perhaps it takes time to develop appropriately balanced languages, or
perhaps people just need time to adjust.

Another example is how best to access relational databases from OO
languages.  The most popular approach seems to have been to emphasise
the objects as much as possible, and then slowly introduce SQL-like
(more declarative) features.  That is how I would (roughly)
characterise the approach taken by, say, Hibernate.

But just as functional ideas are starting to spread into the OO
mainstream, so there are few signs that a more declarative, SQL-like
approach may be useful for some problems.  Perhaps the best example is
LINQ which I have not had the chance to use.

Two other libraries that take a vaguely similar approach (although,
been libraries, they are not sa deeply integrated as I think LINQ is)
are SQLAlchemy for Python and Empire DB for Java.  Both these place
the primary emphasis on constructing SQL queries; building objects
from the results comes second.

Personally, as someone who actually likes using SQL, I find this
approach very interesting.

Recently I started a new, small project, to learn Scala: I decided to
write a playlist generator that would take my MP3 collection and use
metadata to construct graphs of connected tracks.  Given the above I
also decided to try using Eclipse DB.

What follows are some examples from my initial code.  I am still
working on constructing the database, given a set of MP3 files, and I
am sure my code will evolve significantly before I finish.  But what I
have is already interesting and I thought it would be useful to share
it.

Empire DB is at http://incubator.apache.org/empire-db/

The changeset for the code that I have as I write this is at
http://code.google.com/p/uykfd/source/detail?r=a834c704643dc48642bb71e74aa7c4c967ea1da9


I thought I would focus on two areas of the code.  First, the database
definition.  This is used (1) to define the database (Empire DB
creates SQL that builds the schema) and (2) to define instances of
Java classes that will support the construction of type safe queries.

The database definition is here -
http://code.google.com/p/uykfd/source/browse/src/main/scala/org/acooke/uykfd/db/Schema.scala?spec=svna834c704643dc48642bb71e74aa7c4c967ea1da9&r=a834c704643dc48642bb71e74aa7c4c967ea1da9#21
- and I will also cut+paste some examples below.

Here, for example, is a class that describes a table with two columns
- an auto-increment key and some varchar text:

  class IdValue(name: String)
      extends DBTable(name, this) {
    val ID = addColumn("ID", DataType.AUTOINC,
                       0, true, name + "_SEQ")
    val VALUE = addColumn("VALUE", DataType.TEXT,
                          MAX_VARCHAR, true)
    setPrimaryKey(ID)
  }

This can be then instantiated -

  object CANONICALS extends IdValue("CANONICALS")

- to create a table, called CANONICALS, that has two columns (ID and
VALUE), with the types as above.  Later Scala code can refer to those
columns as CANONICALS.ID and CANONICALS.VALUE

Note that Scala's object/class approach makes this code particularly
compact and transparent (at least if you know a little Scala).  With
both Empire DB and SQLAlchemy I have been impressed with how easy it
is to define a schema, including basic foreign key constraints, in a
engine-neutral manner (I am using HSQL, but the same code would work
with, say, Oracle or MySQL).


The second area I wanted to show was the code I use to generate
entries in the database.  This code is *not* as transparent as the
schema.  That is largely because I am writing quite generic code that
is reused for a variety of tables.  I hope I can improve this work.

However, some of the details are still worth showing.  For example,
look at the routines used to extract data from the database -
http://code.google.com/p/uykfd/source/browse/src/main/scala/org/acooke/uykfd/db/Schema.scala?spec=svna834c704643dc48642bb71e74aa7c4c967ea1da9&r=a834c704643dc48642bb71e74aa7c4c967ea1da9#102

These are for all tables that follow the ID/VALUE layout I described
above and the first method, fromValue, constructs a SQL query to fine
the value:

    val cmd = Schema.createCommand
    cmd.select(row.table.getColumns)
    cmd.where(row.table.VALUE.is(value))

Notice how there are no strings used for table names in that snippet.
Everything is defined in terms of the schema described above.

OK, that will have to do for now - I need to get some sleep.

Andrew

Outer Join and Sub-Select Example for Empire DB and Scala

From: andrew cooke <andrew@...>

Date: Thu, 8 Oct 2009 15:04:09 -0400

Here's a nice example where I am clearing out orphaned values (I don't
want to cascade on deletion for various reasons).

  def clean(cnxn: Connection) {
    val subCmd = Schema.createCommand
    subCmd.select(Schema.ARTIST_TAGS.ID)
    subCmd.join(Schema.TRACKS.ARTIST_TAG,
                       Schema.ARTIST_TAGS.ID, DBJoinType.RIGHT)
    subCmd.where(Schema.TRACKS.ID.is(null))
    val orphanArtists = new DBQuery(subCmd)
    val cmd = Schema.createCommand
    cmd.where(Schema.ARTIST_TAGS.ID.in(orphanArtists))
    Schema.executeSQL(cmd.getDelete(Schema.ARTIST_TAGS), cnxn)
  }

The right join constructs a table with all the artists, then I select
those fr which there is no corresponding track (null ID).  That is
used as the sub-select for deletion.

Andrew

And If You Still Don't Get It

From: andrew cooke <andrew@...>

Date: Thu, 8 Oct 2009 15:16:48 -0400

Because it's code, it's easy to reuse:

  def clean(cnxn: Connection) {
    def cleanOrphans(tag: DBColumnExpr, table: Schema.Id) {
      val subCmd = Schema.createCommand
      subCmd.select(table.ID)
      subCmd.join(tag, table.ID, DBJoinType.RIGHT)
      subCmd.where(Schema.TRACKS.ID.is(null))
      val orphans = new DBQuery(subCmd)
      val cmd = Schema.createCommand
      cmd.where(table.ID.in(orphans))
      Schema.executeSQL(cmd.getDelete(table), cnxn)
    }
    cleanOrphans(Schema.TRACKS.ARTIST_TAG, Schema.ARTIST_TAGS)
    cleanOrphans(Schema.TRACKS.ALBUM_TAG, Schema.ALBUM_TAGS)
    cleanOrphans(Schema.TRACKS.SONG_TITLE_TAG, Schema.SONG_TITLE_TAGS)
  }

Andrew

Comment on this post