haul 02/04/28 11:14:45
Modified: src/documentation/xdocs/userdocs/actions book.xml
Added: src/documentation/xdocs/userdocs/actions
database-actions.xml
Log:
docs for database operations and modules
Revision Changes Path
1.2 +1 -0 xml-cocoon2/src/documentation/xdocs/userdocs/actions/book.xml
Index: book.xml
===================================================================
RCS file: /home/cvs/xml-cocoon2/src/documentation/xdocs/userdocs/actions/book.xml,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
--- book.xml 3 Jan 2002 12:31:04 -0000 1.1
+++ book.xml 28 Apr 2002 18:14:45 -0000 1.2
@@ -12,6 +12,7 @@
<menu label="Actions">
<menu-item label="Overview" href="actions.html"/>
+ <menu-item label="Database" href="database-actions.html"/>
</menu>
<menu label="Default">
</menu>
1.1
xml-cocoon2/src/documentation/xdocs/userdocs/actions/database-actions.xml
Index: database-actions.xml
===================================================================
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.0//EN"
"../../dtd/document-v10.dtd">
<document>
<header>
<title>Database Actions</title>
<authors>
<person name="Christian Haul" email="[EMAIL PROTECTED]"/>
</authors>
</header>
<body>
<s1 title="Introduction">
<p>
Two different sets of actions exist, that deal with (object) relational
database access through JDBC. The original database actions provide a
relatively simple interface to store, modify, delete and retrieve data.
They are oriented towards usage of request parameters for input and
request attributes together with sitemap variables for output and do
not support auto increment column types. In addition, the description
of
the database structure is split over several files since these actions
attempt to use all tables in a provided description.
</p>
<p>
The modular database actions provide similar functionality. In contrast
to the original actions they allow to store the database meta data in a
single file and to switch input and output flexible through the use of
modules. Even for auto increment columns specific modules exist that
cover a wide range of database management systems.
</p>
</s1>
<s1 title="Original Database Actions">
<p>
The original database actions have evolved quite a bit and at different
speeds. The add action is certainly the most complete one, providing
support for multiple tables and rows. However, the interface has become
a bit inconsistent.
</p>
<p>
If an error occurs, the original database actions will throw an
exception.
</p>
<s2 title="Describing the Structure of your DB - descriptor.xml">
<p>
The key to database actions is a file that describes database meta
data in XML. The original actions will ignore all but the first table
and act only on one row. Only the add action will try to access all
tables that are contained in this description. As a consequence, each
HTML form needs to have a corresponding descriptor file if different
tables are affected.
</p>
<p>
The file name has no meaning and does not need to be
<code>descriptor.xml</code> - it can even be a Cocoon pipeline. The
name of the root element in a descriptor file is ignored. Only
<code>table</code> elements nested on first level inside the root
element are parsed by the actions. All unknown elements or attributes
are ignored.
</p>
<p>
For each table a <code>table</code> element needs to be present.
</p>
<source>
<![CDATA[
<?xml version="1.0"?>
<employee>
<connection>personnel</connection>
<table name="employee">
<keys>
<key param="employee" dbcol="id" type="int" mode="manual"/>
</keys>
<values>
<value param="name" dbcol="name" type="string"/>
<value param="department" dbcol="department_id" type="int"/>
</values>
</table>
</employee>
]]>
</source>
<p>
Describes a single table named "employee". In addition a database
connection is specified. See <link
href="../../developing/datasources.html">here</link> for more
information on database connections.
</p>
<s3 title="Key Columns">
<p>
Tables may or may not have key columns. A key column is a
column
that is part of the primary key. Actually, candidate keys
should do
as well.
</p>
<p>
All key columns are contained in a <code>keys</code> child
element
of the <code>table</code> element. Each column has a
<code>key</code> element to define its properties. The
<code>dbcol</code> attribute holds the column name,
<code>type</code> is the JDBC type name for this column (have a
look at AbstactDatabaseAction source for valid type names),
<code>param</code> specifies the name of the request parameter
to
use, and <code>mode</code> sets how the value for this column
is
obtained on adding a row.
</p>
<p>
Through the mode attribute the behaviour of the add action can
be
changed.
</p>
<p>
Default mode is "automatic" and to let the database create the
key
value by setting this value to <code>null</code>. The created
value
can not be read back from the database and will not be
available as
request attribute or sitemap variable.
</p>
<p>
A mode of "manual" will query the database for the maximum
current
value, add 1 to it and use that for a value.
</p>
<p>
A mode of "form" will use the corresponding request parameter.
</p>
<p>
A mode of "request-attribute" will use the corresponding
request
attribute. The name specified in the <code>param</code>
attribute
will be automatically prefixed with the class name.
</p>
<p>
Key values will be propagated to sitemap variables and -
prefixed
with the class name - request attributes.
</p>
</s3>
<s3 title="Other Columns">
<p>
All other columns are contained in a <code>values</code> child
element of the <code>table</code> element. Each column has a
<code>value</code> element to define its properties.
Properties are
similar to those for key columns. A <code>mode</code> attribute
does not exist for value columns. Instead, request parameters
and
request attributes are tried in this order for the specified
parameter.
</p>
<p>
Request attribute names are <em>not</em> prefixed with the
class
name. Thus, to insert the value of a key column of the
previous row
or previous table into a value column, it needs to be named
<code>org.apache.cocoon.acting.AbstractDatabaseAction:key:table:dbcol</code>.
</p>
<p>
Value columns are propagated to request attributes with class
name
prefix. They are not available for the sitemap.
</p>
</s3>
</s2>
</s1>
<s1 title="Modular Database Actions">
<p>
The modular database actions were mainly created to make auto increment
columns available, handle input and output flexibly, and have a
consistent interface. A successful action will return the number of
rows affected in a sitemap parameter named <code>row-count</code>. The
added features required to change the descriptor file format in
incompatible ways.
</p>
<p>
It can be configured if an exception will be thrown when an error
occurs.
</p>
<s2 title="Describing the Structure of your DB - descriptor.xml">
<p>
Like the original actions, the modular actions need meta data in an
XML file. However, that file may contain any number of tables, not
just the ones needed for a single request. The tables actually used
are referenced through a <code>table-set</code>. Unknown elements and
attributes are ignored. This way a descriptor file can be shared with
other actions like the form validator.
</p>
<p>
For the flexible input and output handling, the modular database
actions rely on <link href="../concepts/modules.html">modules</link>.
Have a look at those before proceeding.
</p>
<p>
The following is a snippet from a descriptor file.
</p>
<source>
<![CDATA[
<root>
<connection>personnel</connection>
<table name="user" alias="user">
<keys>
<key name="uid" type="int" autoincrement="true">
<mode name="auto" type="autoincr"/>
</key>
</keys>
<values>
<value name="name" type="string"></value>
<value name="firstname" type="string"></value>
<value name="uname" type="string"></value>
</values>
</table>
]]>
</source>
<p>
The <code>table</code> element has an additional attribute
<code>alias</code> which is an alternative name to reference
the table from a table set. The descriptor file is searched
top down for tables whose <code>name</code> or
<code>alias</code> match. The <code>alias</code>n attribute
is useful if a complex join expression is used as table
name. In such a case modifications like update, insert,
delete will likely fail.
</p>
<p>
Another application of aliases if different numbers of columns should
be affected by an operation. or if a table contains several candidate
keys that are used alternatively. This way, different views to a
table can be created.
</p>
<s3 title="Key Columns">
<p>
The descriptor file resembles the one for the original
actions. One
major difference is the absence of <code>dbcol</code> and
<code>param</code> attributes. Instead there is a
<code>name</code>
attribute which corresponds to the <code>dbcol</code>
attribute and
specifies the database column name.
</p>
<p>
If a column is an auto increment column, the similar named
attribute
indicates this. Auto increment columns will be handled
differently
on insert operations.
</p>
<p>
Instead of specifying a parameter name, the actions support to
use
different input modules for each operation through the nested
<code>mode</code> elements. This is described in more detail
below.
</p>
<p>
Note here though, that not every column needs a
<code>mode</code>
element: The actions default to the module defined as
<code>request</code> which is in a default installation to
obtain
the values from request parameters. The name of the parameter
defaults to table name dot column name.
</p>
</s3>
<s3 title="Other Columns">
<p>
Apart from the fact that the auto increment columns are only
supported for key columns, everything said above applies to
value
columns as well.
</p>
</s3>
<s3 title="Operation Mode Types">
<p>
Basically, two different mode types exist:
<code>autoincrement</code> which is used whenever data shall be
inserted into a table and this particular key column has the
auto increment attribute set and <code>others</code> for all
other
requirements.
</p>
<p>
In addition, a table-set can specify different mode types to use
instead of the predefined type names. Through this, and the
fact
that every mode can specify a different input module, it is
easy to
use different input modules for different tasks and forms.
</p>
<p>
One special mode type name exists that matches all requested ones:
<code>all</code> This makes it easier to configure only some
columns differently for each table-set.
</p>
</s3>
<s3 title="How to obtain Values">
<p>
As said above, these actions default to reading from request
parameters with a default parameter name. By specifying
<code>mode</code> elements, this can be overridden. Any
component
that implements the <code>InputModule</code> interface can be
used
to obtain values. How to make such modules known to Apache
Cocoon
is described <link
href="../concepts/modules.html">elsewhere</link>.
</p>
<p>
Beside using different input modules, their parameters can be
set
in place, for example to override parameter names, configure a
random generator or a message digest algorithm.
</p>
<source>
<![CDATA[
<table name="user_groups">
<keys>
<key name="uid" type="int">
<mode name="request" parameter="user_groups.uid" type="request"/>
<mode name="attribute"
parameter="org.apache.cocoon.components.modules.output.OutputModule:user.uid[0]"
type="attrib"/>
</key>
<key name="gid" type="int" set="master">
<mode name="request" parameter="user_groups.gid" type="all"/>
</key>
</keys>
</table>
]]>
</source>
<p>
The above example shows just that: the <code>parameter</code>
attribute is not read by the database action itself but the
complete <code>mode</code> configuration object is passed to
the
input module. Both the request attribute and the request
parameter
input modules understand this parameter attribute which takes
precedence over the default one.
</p>
<p>
Another feature when obtaining values is tied to the
<code>type</code> attribute: Different modes can be used in
different situations. The basic setup uses two different mode
types: <code>autoincrement</code> when inserting in key columns
that have an indicator that they are indeed auto increment
columns
and <code>others</code> for insert operations on all other
columns
and all other operations on all columns.
</p>
<p>
Table-sets can override the default names for these two mode
type
name categories with arbitrary names except the special name
<code>all</code>. A mode that carries the type name "all" is
used
with all requested type names. Lookup obeys first match
principle
so that all modes are tested from top to bottom and the first
that
matches is used.
</p>
</s3>
<s3 title="How to store Values e.g. in your Session">
<p>
All modular database action can be configured to use any
component
that implements the <code>OutputModule</code> interface to
store
values. The output module is chosen on declaring the action in
the
sitemap or dynamically with a sitemap parameter. If no output
module is specified, the default it to use the request
attribute
module.
</p>
<p>
The interface does not allow to pass configuration information
to
the output module. This has to be done when the module is
declared
e.g. in cocoon.xconf.
</p>
</s3>
<s3 title="Inserting Multiple Rows - Sets">
<p>
Once common task is to work on more than one row. If the rows
are
in different tables, this is catered for by table-sets.
Operating
on multiple rows of one table requires to mark columns that
should
vary and among those one, that determines the number of rows to
work on.
</p>
<p>
This is done with sets. All columns that cary a
<code>set</code>
attribute can vary, those, that don't, are kept fixed during
the
operation. The column that is used to determine the number of
rows
is required to have a value of <code>master</code> while all
others
need to have a value of <code>slave</code> for the set
attribute. There may be only one master in a set.
</p>
<p>
Sets can be tagged either on column or on mode level but not
both
for a single column.
</p>
</s3>
<s3 title="Select Your Tables - Table-Sets">
<p>
Tables that should be used during an operation can be grouped
together with a table-set. A table-set references tables by
their
name or their alias.
</p>
<p>
In addition, a table-set can override the mode type names for
the
two categories "autoincrement" and "others".
</p>
<p>
Operations spanning multiple tables in a table-set are done in
a
single transaction. Thus, if one fails, the other is rolled
back.
</p>
<source>
<![CDATA[
<table name="groups">
<keys>
<key name="gid" type="int" autoincrement="true">
<mode name="auto" type="autoincr"/>
</key>
</keys>
<values>
<value name="gname" type="string"/>
</values>
</table>
<table-set name="user">
<table name="user"/>
</table-set>
<table-set name="groups">
<table name="groups"/>
</table-set>
<table-set name="user+groups">
<table name="user"/>
<table name="user_groups" others-mode="attrib"/>
</table-set>
<table-set name="user_groups">
<table name="user_groups" others-mode="request"/>
</table-set>
</root>
]]>
</source>
</s3>
</s2>
</s1>
</body>
</document>
----------------------------------------------------------------------
In case of troubles, e-mail: [EMAIL PROTECTED]
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
