Mittwoch, 25. Juni 2014

Quoted Identifiers in Oracle

The default setting of Oracle's Data Modeler is to generate a DDL file without quoted identifier. This involves the danger of name collisions. It is not possible to call a table "TABLE", because "TABLE" is an identifier of the data definition language. The list of standard identifiers is quite long and the list of vendor specific extensions is much longer. It is impossible to know all identifiers to prevent name collisions. But it is quite simple to avoid any name collisions by quoting the identifiers. If you use quoted identifiers you do not need to care any longer about identifiers.

The following screen shot shows where to enable quoted identifiers in Oracle's Data Modeler.

But you have to consider MySQL's incompatibility. MySQL conforms not to the SQL standard. The SQL standard specifies that quoted identifiers must be quoted with a double quote. But MySQL uses back quotes instead to quote an identifier.

Renaming primary keys in the logical model of Oracles Data Modeler

In the past I explained already how to rename inheritance relations. Now I will show a small script to fix wrong names of primary key constraints. This is necessary, if an entity gets renamed. In this case the primary key constraint has still the old name of the entity according to the naming convention, which was active when the primary key has been created.

entities = model.getEntitySet().toArray();
for (var e = 0; e < entities.length; e++) {
  entity = entities[e];
  entity_name = entity.getName();
  primarykey = entity.getPK();
  primarykey_name = primarykey.getName();
  new_primarykey_name = entity_name.toUpperCase() + "_PK";
  if (primarykey_name != new_primarykey_name) {

This script works on the logical model and sets all primary key names to the upper case of the entity name followed by "_PK".

Mittwoch, 11. Juni 2014

Extract the Class-Path from a JAR using SED

The Class-Path in a manifest file of a JAR exceeds in most cases the line width limit of manifest files. In this case the line is continued in the next line which starts with a space. In order to read the class path from a manifest file it is necessary to join the lines. The following sed command does it on Unix.

unzip -c example.jar META-INF/MANIFEST.MF |
sed -n '/^Class-Path: /,/^[^ ]/{s/^\(Class-Path:\)\? //;H};${g;s/\r\?\n//g;s/ /:/g;p}'

The command replaces the spaces in the class path of a manifest file with colons. The result can be used directly as an argument to a -classpath option.

Freitag, 6. Juni 2014

Using Saxon-HE as a XPath command line tool

Subversion can print the repository information in XML format.

svn info --xml

This makes it easy to extract the interesting parts in a Shell script, if an XPath tool is available. Newer versions of xmllint provide such a functionality. On those Systems which do not provide any suitable xmllint but provide a Java RE it is possible to use Saxon-HE. But the command line options are not very intuitive. The following example shows how to get the URL for the repository root.

saxon () { java -cp Saxon-HE-9.5.1-5.jar net.sf.saxon.Query "$@" ; }
xpath () { saxon '!method=text' -s:- -qs:"$1" ; }
svn info --xml | xpath '/info/entry/repository/root/text()'

The Saxon-HE JAR can be found in the Maven repository.

Donnerstag, 5. Juni 2014

Configure Emacs 24.3 on Red Hat Enterprise Linux 5.10

The following packages are required on Red Hat 5 to configure Emacs 24.3.

yum install gnome-desktop-devel libXpm-devel libjpeg-devel giflib-devel libtiff-devel ncurses-devel librsvg2-devel libselinux-devel

Emacs 24.3 requires GNU TLS 2.6.6, which is not available on Red Hat 5. Installing gnutls-devel does not help, because only version 1.4 of GNU TLS will be installed.