SQL Transformer
+ +Introduction
+The purpose of the SQLTransformer is to query a database and translate the +result to XML. To retrieve the information from the database, you are not +restricted to use simple SQL statements (e.g. select, insert, update), it is +also possible to use stored procedures. In combination with other transformers +(e.g. FilterTransformer), this one can be very powerful.
+-
+
+
- Name: sql + +
- Class: org.apache.cocoon.transformation.SQLTransformer + +
- Cacheable: no + +
Basic functionality
+To be able to query a database, we need XML that describes exactly what we +want to do. The general structure of this input XML is as follows:
++ + <page> + <sql:execute-query xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:query> + <!-- here comes the SQL statement or stored procedure --> + </sql:query> + </sql:execute-query> + </page> ++
Nothing prevents you from putting other XML around the execute-query +element. Any element not in the SQL namespace will stay untouched. The format of +the SQL statement or the stored procedure is exactly the same as if you would +call it directly from java with a prepared statement or a callable statement. +
+The query element has the following optional attributes:
+-
+
+
-
+name: Naming a query implicates naming the corresponding
+rowset (see below). When you have a sequence of queries you want to execute, it
+can be handy give them a name. To process the retrieved data of a certain query,
+you can use another transformer to check the name of the rowset and to execute
+the necessary business logic on it.
+usage: <sql:query name="myName"> +
+
+ -
+isstoredprocedure: When you want to use stored procedures,
+you have to explicitly add this attribute to the query element. By default, the
+transformer assumes that you want to execute a SQL statement.
+usage: <sql:query isstoredprocedure="true"> +
+
+
Here is an example of how the input XML might look like:
++ + <page> + <title>Hello</title> + <content> + <para>This is my first Cocoon page filled with sql data!</para> + <sql:execute-query xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:query name="department"> + select id,name from department_table + </sql:query> + </sql:execute-query> + </content> + </page> ++
You can use the file generator to retrieve the XML from the filesystem. To +invoke the SQLTransformer you have to add following to the sitemap:
++ + <map:transform type="sql"> + <map:parameter name="use-connection" value="personnel"/> + <map:parameter name="show-nr-of-rows" value="true"/> + <map:parameter name="clob-encoding" value="UTF-8"/> + </map:transform> ++
The use-connection parameter defines which connection, defined under +the datasources element in cocoon.xconf, the SQLTransformer has to use +to retrieve the data.
+The show-nr-of-rows instructs the transformer to count the number of +rows in the resultset explicitly and to set the result as attribute to the +rowset element. This attribute is only useful in combination with a sql +statement, not with stored procedures. If a stored procedure returns a resultset +and you want to know how many rows it contains, you have to count the number of +rows in another transformer or your stored procedure has to return it also (last +solution is the best one).
+The clob-encoding parameter defines what encoding should be used in +getting content from CLOB columns.
+The output XML will look as follows:
++ + <page> + <title>Hello</title> + <content> + <para>This is my first Cocoon page filled with sql data!</para> + <sql:rowset nrofrows="2" name="department" + xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:row> + <sql:id>1</sql:id> + <sql:name>Programmers</sql:name> + </sql:row> + <sql:row> + <sql:id>2</sql:id> + <sql:name>Loungers</sql:name> + </sql:row> + </sql:rowset> + </content> + </page> ++
If you use this in combination with the simple-sql2html.xsl +stylesheet,
++ + <map:transform src="stylesheets/simple-sql2html.xsl"/> ++
you will get a more visually attractive page.
+See below for a more in depth example with stored procedures.
+By now you should be able to use the SQLTransformer, but there are some more +options you might find useful...
+Advanced functionality
+Substitution
+Sometimes you need more information before you can execute a query, e.g. the +name of the user that is currently logged on your site. This information is only +available at runtime and hence can only be substituted in the query when +available.
+To pass this information to the SQL statement, the input XML has to look like +this:
++ + <page> + <sql:execute-query xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:query> + select id,name from employee_table where name = + '<sql:substitute-value name="username"/>' + </sql:query> + </sql:execute-query> + </page> ++
The substitution is done by the SQLTransformer before it executes the query +(before it calls the method prepareStatement!). For this, the +transformer has to be given the necessary values via the sitemap (as parameter): +
++ + <map:transform type="sql"> + <map:parameter name="use-connection" value="personnel"/> + <map:parameter name="show-nr-of-rows" value="true"/> + <map:parameter name="username" value="Stefano Mazzocchi"/> + </map:transform> ++
Whenever the transformer encounters a substitute-value element for +which the attribute name contains the value username, it will +replace this element with the value Stefano Mazzocchi.
+The output XML will be as follow:
++ + <page> + <sql:rowset nrofrows="1" xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:row> + <sql:id>2</sql:id> + <sql:name>Stefano Mazzocchi</sql:name> + </sql:row> + </sql:rowset> + </page> ++
It is also possible to use substitution in combination with stored +procedures.
+ +Ancestors
+This functionality is best described by a simple example.
+Take following input XML:
++ + <page> + <sql:execute-query xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:query name="department"> + select id, name from department_table + </sql:query> + <sql:execute-query> + <sql:query name="employee"> + select id, name from employee_table where department_id = + <sql:ancestor-value name="id" level="1"/> + </sql:query> + </sql:execute-query> + </sql:execute-query> + </page> ++
The first query will retrieve all id's and name's from the +department_table table. For each id that comes from the +department_table, the second query, in which the +ancestor-value element will be replaced by the id, will be +executed. The above example will be transformed to the following XML:
++ + <page> + <sql:rowset nrofrows="2" name="department" + xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:row> + <sql:id>1</sql:id> + <sql:name>Programmers</sql:name> + <sql:rowset nrofrows="2" name="employee"> + <sql:row> + <sql:id>1</sql:id> + <sql:name>Donald Ball</sql:name> + </sql:row> + <sql:row> + <sql:id>2</sql:id> + <sql:name>Stefano Mazzocchi</sql:name> + </sql:row> + </sql:rowset> + </sql:row> + <sql:row> + <sql:id>2</sql:id> + <sql:name>Loungers</sql:name> + <sql:rowset nrofrows="1" name="employee"> + <sql:row> + <sql:id>3</sql:id> + <sql:name>Pierpaolo Fumagalli</sql:name> + </sql:row> + </sql:rowset> + </sql:row> + </sql:rowset> + </page> ++ +
in- and out-parameters
+Stored procedures can return data as a parameter. To make use of this +functionality in java, you have to register these parameters as out +parameters. Since this information is application specific, the +SQLTransformer uses reflection to retrieve the data in the right format. For +this, an extra element is needed in the input XML:
++ + <sql:out-parameter nr="1" + name="code" + type="java.sql.Types.INTEGER"/> ++
where:
+-
+
+
- +nr: The targeted parameter number that will return data of +a certain type. + +
- +type: The type of data that will be returned (defined in +java.sql.Types or in database specific drivers, e.g. +oracle.jdbc.driver.OracleTypes). Once the stored procedure returns data +in the parameters, the stored procedure tries to process them. If the returned +parameter is an instance of ResultSet, it will be translated to XML as +we saw before. In all the other situations the SQLTransformer will convert the +parameter to a string. + +
This is an example of how to call an oracle stored procedure and process it +with the SQLTransformer:
+
+
+ <page>
+ <sql:execute-query xmlns:sql="http://apache.org/cocoon/SQL/2.0">
+ <sql:query isstoredprocedure="true" name="namesearch">
+ begin QUICK_SEARCH.FIND_NAME('<sql:substitute-value
+ name="username"/>',?,?,?); end;
+ </sql:query>
+ <sql:out-parameter nr="1" name="code"
+ type="java.sql.Types.INTEGER"/>
+ <sql:out-parameter nr="2" name="nrofrows"
+ type="java.sql.Types.INTEGER"/>
+ <sql:out-parameter nr="3" name="resultset"
+ type="oracle.jdbc.driver.OracleTypes.CURSOR"/>
+ </sql:execute-query>
+ </page>
+
+The SQLTransformer will create 3 elements, respectively code, +nrofrows and resultset under the element namesearch. +Since the type oracle.jdbc.driver.OracleTypes.CURSOR corresponds to a +ResultSet, a rowset element will be created, containing all +the data of the resultset. It is also possible to use an in-parameter +element, e.g. <sql:in-parameter nr="1" value="1"/>. This +functionality is only provided to be complete, because it is available in Java +itself. You can also use the in-parameter in combination with a SQL +statement. Used in combination with an out-parameter, a +?-parameter can be an in-parameter and an +out-parameter at the same time.
+Combined with other transformers
+FilterTransformer
+When you query a database and it returns too many rows to process at once, +you might want to take a block of elements, process this block and ignore the +rest for now. You can best compare it to a search on Google: they only return 10 +results in one time, for more results you have to click on another block (page). +It wouldn't be wise to process more than 10 elements in the pipeline if you only +need to display 10 elements.
+Assume that a query returns 56 row elements (by using the SQLTransformer) and +that you only want to display the first 10 elements:
+Output XML from the SQLTransformer:
++ + <sql:rowset nrofrows="56" name="test" + xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <sql:row> + <!-- db record --> + </sql:row> + <sql:row> + <!-- db record --> + </sql:row> + + ... + + <sql:row> + <!-- db record --> + </sql:row> + </sql:rowset> ++
By adding following lines to the sitemap, just under the SQLTransformer, you +restrict the results to 10 elements in the first block:
++ + <map:transform type="filter"> + <map:parameter name="element-name" value="row"/> + <map:parameter name="count" value="10"/> + <map:parameter name="blocknr" value="1"/> + </map:transform> ++
output XML:
++ + <sql:rowset nrofrows="56" name="test" + xmlns:sql="http://apache.org/cocoon/SQL/2.0"> + <block id="1"> + <sql:row> + <!-- db record --> + </sql:row> + + <!-- total of 10 rows --> + + <sql:row> + <!-- db record --> + </sql:row> + </block> + <block id="2"/> + <block id="3"/> + <block id="4"/> + <block id="5"/> + <block id="6"/> + </sql:rowset> ++
To make it more dynamically, put something like {reqCount} and +{reqBlock} in the values for count and blocknr +respectively. These can be parameters from the request and they can be passed to +the sitemap with an action.
+The FilterTransformer is a standalone component; you don't need to use it in +combination with the SQLTransformer.
+ +WriteDOMSessionTransformer
+If you only use the FilterTransformer in combination with the SQLTransformer, +you have to query the database each time the user wants to see another part of +the result. You can better store the result in the session after the first +request and retrieve the result from the session for the subsequent requests. +This can be done by using a selector, which checks if the data is available in +the session or not.
+WriteDOMSessionTransformer can build a DOM starting from a given element +(which will be the root of the DOM tree) and store it in the session. If you +want to store the result of a query, you have to add following to the sitemap: +
++ + <map:transform type="writeDOMsession"> + <map:parameter name="dom-name" value="DBresult"/> + <map:parameter name="dom-root-element" value="rowset"/> + </map:transform> ++
The transformer will build a DOM tree with rowset as root element +and will store it in the session with the name DBresult.
+The WriteDOMSessionTransformer is a standalone component, you don't need to +use it in combination with the SQLTransformer.
+ +ReadDOMSessionTransformer
+Simply transforms a DOM to SAX events, which can be used further on in the +pipeline. Once you stored the result of a query in the session with the +WriteDOMSessionTransformer, you can read it again with the +ReadDOMSessionTransformer:
++ + <map:transform type="readDOMsession"> + <map:parameter name="dom-name" value="DBresult"/> + <map:parameter name="trigger-element" value="users"/> + <map:parameter name="position" value="after"/> + </map:transform> ++
In this example the SAX events, that come from the DOM tree stored in the +session with name DBresult, will be added after the users +element. This means as soon that the transformer encounters the end element +users, it will start to generate SAX events from the DOM tree. There +are three possible positions, before, in and after: +
+-
+
+
- +before means that when the transformer encounters +the users element, it will FIRST translate the DOM tree to SAX events +and THEN it will continue to forward the other SAX events (starting with +users). + +
- +in means that the transformer will forward the +start element event for users and that it IMMEDIATELY starts to +generate SAX events from the DOM tree. After that, it will continue to forward +the child elements of users and then all the other elements. + +
- +after means that the transformer starts to +generate SAX events from the DOM tree just after it has forwarded the end +element users. + +
The ReadDOMSessionTransformer is a standalone component, you don't need to +use it in combination with the WriteDOMSessionTransformer.
+That's it,
+Sven Beauprez
++Errors and Improvements? + If you see any errors or potential improvements in this document + please help us: + + View, Edit or comment on + the latest development version (registration required). +
+