Elements of a Data Service

Data services and resources provide a service-and-resource-interface to some data stored in a relational database. In a service interface, you must indicate how service requests map to queries against collections of tables in a relational database and how query results are mapped to service responses. In a resource interface, you must indicate how a set of resources map to queries and how query responses are returned as resource representations (or reports of resource creation or deletion, depending on the HTTP verb in use).

The following topics describe the data services configuration language and the key elements used when composing a data service, such as queries, databases, operations etc. along with example syntax.

[ Data services and resource language ] [ Configuring the datasource ] [ Defining queries ] [ Defining service operations ] [ Defining resources ] [ Defining event trigger ] [ Security configuration ] [ Sample data service configuration ]

Data services and resource language

Data services and resources are defined using the Data Services and Resource Language (DSRL) where a <data> element describes a data service or a resource. The common attributes of a <data> element is given in the following example:

<data baseURI="xs:anyURI" name="xs:NMTOKEN" enableBatchRequests="xs:BOOLEAN" enableBoxcarring="xs:BOOLEAN" txManagerJNDIName="xs:NMTOKEN" serviceNamespace="xs:anyURI" serviceGroup="xs:NMTOKEN" serviceStatus="active|inactive" transports="http https JMS local" >
    config+
    query+
    operation+
    resource+
    event-trigger+
</data>

Attribute	Description
baseURI	a REQUIRED URI indicating the base URI for the operations and resources definedwithinthe <data> element.
name	a REQUIRED name of the data service.
enableBatchRequest	an OPTIONAL boolean to enable the batch request feature.
enableBoxcarring	an OPTIONAL boolean to enable theboxcarringfeature.
txManagerJNDIName	an OPTIONAL JNDI name for overriding the standard JNDI location for locating the JTA transaction manager
serviceNamespace	an OPTIONAL URI to uniquely identify the web service.
serviceGroup	an OPTIONAL name that is used to categorizedata-servicesin different groups.
serviceStatus	an OPTIONAL string to enable WIP (specifiesweatherthe data service is deployed or work in progress) support.
transports	an OPTIONAL string to enable the transports required for the data service. The possible values are "http", "https", "JMS" and "local".

Configuring thedatasource

The following sample config gives the common elements used to connect to a datasource:

<config id="xs:ID">
    <property name="xs:NMTOKEN">xs:urType</property>+
</config>

config/@id: an OPTIONAL XML ID identifying the config element. If the configuration file has multiple <config> elements, then this attribute is required.

The actual set of properties is defined by each type of database connection (e.g., JDBC will have its own standard set).

Defining queries

A query consists of parameters that describe how to map the result to an XML element. It is similar to a function that maps some parameters to an XML element. A query definition does not indicate how the parameters are acquired. Instead, it just lists the parameters that are needed, assuming that the parameters will be provided. If the query is at a top level (i.e., direct child of <data>) then either an operation definition or a resource definition provides the context for the parameters. If the query is nested within a <result> element, then the parameter names refer to column names of the result table described in the <result> element of the XML.

The following sample config shows the common attributes of a <query> element:

<query id="xs:ID"?  useConfig="xs:ConfigID" returnGeneratedKeys="xs:BOOLEAN">
    <param name="xs:NMTOKEN" sqlType="xs:string"  paramType="SCALAR | ARRAY"  type="IN | OUT | IN-OUT" ordinal="xs:integer"   defaultValue="xs:string" />*
           ( <validateCustom class= "xs:string"/> | <validateLength minimum="xs:integer" maximum="xs:integer" /> | <validatePattern pattern="xs:string" />)
      </param>
    ( <sql dialect="xs:NMTOKEN">xs:string</sql>+ | <sparql>xs:string</sparql> )
    <properties>
        <property name="xs:NMTOKEN">xs:string</property>+
    </properties>
    <result element="xs:QName" rowName="xs:QName"  defaultNamespace="xs:anyURI" />
        (element | attribute | call-query )*
    </result>
</query>

<element name="xs:QName" column="xs:NMTOKEN" requiredRoles="xs:NMTOKEN" export="xs:NMTOKEN" exportType="SCALAR | ARRAY" xsdType="xs:QName">
     (element | attribute | call-query )*
</element>

<attribute name="xs:QName" column="xs:NMTOKEN" requiredRoles="xs:NMTOKEN" export="xs:NMTOKEN" exportType="SCALAR | ARRAY" xsdType="xs:QName"/>

<call-query href="xs:NCName"         requiredRoles="xs:NMTOKEN" >
            <with-param name="xs:string" query-param="xs:string" />*
</call-query>

Attributes	Sub-attributes	Sub-attributes	Description
id			an OPTIONAL XML ID identifying the query. If <query> is a direct child of <data> then this attribute is required.
useConfig			a REQUIRED reference tothedatasourcethatis to be usedforquery.
returnGeneratedKeys			an OPTIONAL boolean parameter to enable returnGeneratedKeys. Set this attribute to true only in INSERT queries, where the query inserts to a table that has an auto incrementing key column. In such a case, an auto incremented key value is added to the results set. Also see Returning Generated Keys.
param			a declaration of a parameter of the query
	name		a REQUIRED name of the parameter.
	sqlType		an OPTIONAL string containing a legal SQL type which defines the type of the parameter. If none is specified then defaults to string.
	paramType		a REQUIRED parameter type. If none is specified then defaults to SCALAR.
	ordinal		a REQUIRED only for stored procedures which map the parameter positions with the query.
	defaultValue		an OPTIONAL default value of the input parameter.
	validateCustom	class	a REQUIRED custom validation class to validate the input parameter.
	validateLength	minimum	a REQUIRED integer when specifying the minimum length of the parameter.
		maximum	a REQUIRED integer when specifying the maximum length of the parameter.
	validatePattern	pattern	a REQUIRED string pattern to validate the string input parameter.
sql			a REQUIRED string containing the SQL query or SQL function to execute. See Calling an SQL Function in a Query.
	dialect		an OPTIONAL string containingjdbcdriver prefix when need to usesql-dialects.
sparql			a REQUIRED string containing thesparqlquery to execute when using RDF asdatasource.
properties			an OPTIONAL XML to define advanced query properties. Each property is defined as a child element of this.
	name		a REQUIRED name of the property.
result			a REQUIRED elementdescriibinghow the table resulting from executing the query will be converted to an XML element. If any <column> or <query> child elements are present, then ONLY those are transferred as child elements of the result element (or elements, depending on whether result/@rowName is given or not). The order of the nested <column> or <query> elements defines the order of elements in the result element.
	element		a REQUIRED QName which is the name of the element which will hold the results.
	rowName		an OPTIONAL QName which is the name of the element wrapping each row of the result table if more than one element from the table is to be returned. If this attribute is not given, then only the first row is returned and hence no second level wrapper element is needed.
	defaultNamespace		an OPTIONAL URI being the default namespace to use for the namespace name of elements and attributesthat result columnsare mapped to. Defaultsto "" (meaning no namespace).
	call-query		an OPTIONAL element (which may occur any number of times) which is used to execute a further query and produce an element which will be present in the parent element as a child. This is used primarily to use a value of a column as key to select data from a new table.
	element		an OPTIONAL element (which may occur any number of times) indicating how a specific column in the result table is to be mapped into an element
		element/@name	a REQUIRED QName giving the name of the element to put the column data into
		element/@column	an OPTIONAL string giving the name of the column whose value is to be copied into the element.
		element/@requiredRoles	an OPTIONAL string giving the names of roles that who has permission to see the result element. Bydefaultit has set to all users.
		element/@export	an OPTIONAL name giving to the element that to be export outside of query. This feature is used withboxcarringsupport.
		element/@exportType	a REQUIRED parameter when using export option. Used to give the export element type whether scalar or array.
		element/@xsdType	an OPTIONAL indication of the XML Schema type of the element. If none is given defaults to the mapping of the SQL type of the result column named by @column to an XML Schema type as per [SQL XML Mapping]
	attribute		an OPTIONAL element (which may occur any number of times) indicating how a specific column in the result table is to be mapped into an attribute of the element representing the current row
		attribute/@name	a REQUIRED QName giving the name of the attribute to put the column data into
		attribute/@column	an OPTIONAL string giving the name of the column whose value is to be copied into the attribute. Either @column or @param is required.
		attribute/@param	an OPTIONAL string giving the name of the param whose value is to be copied into the attribute. Either @column or @param is required.
		attribute/@requiredRoles	an OPTIONAL string giving the names of roles that who has permission to see the result attribute. Bydefaultit has set to all users.
		attribute/@export	an OPTIONAL name giving to the attribute that to be export outside of query. This feature is used withboxcarringsupport.
		attribute/@exportType	a REQUIRED parameter when using export option. Used to give the export element type whether scalar or array.
		attribute/@xsdType	an OPTIONAL indication of the XML Schema type of the attribute. If none is given defaults to the mapping of the SQL type of the result column named by @column to an XML Schema type as per [SQL XML Mapping]
	call-querry		an OPTIONAL element (which may occur any number of times) indicating how a specific column in the result table is to be mapped into a query result.
		with-param/@name	a REQUIRED name of the query to put the column data into
		with-param/@query-param	an OPTIONAL string giving the name of the column whose value is to be copied into the element.

Defining service operations

Operation refers to a Web service operation defined by a query. The operation is defined as an invocation of a query indicating how the parameters of the query are computed or derived. The syntax is as follows:

<operation name="xs:NCName" disableStreaming="xs:BOOLEAN"/>
    <description>"xs:string"</description>
    <call-query href="xs:IDREF"      />
        <with-param name="xs:NMTOKEN" (query-param="xs:NMTOKEN" | column="xs:NMTOKEN | param="xs:NMTOKEN")/>
    </call-query>
</operation>

operation/@name: is the REQUIRED name of the operation.
operation/@disableStreaming: an OPTIONAL boolean that used to disable streaming. By default streaming are enable.
operation/@description: an OPTIONAL string used to describeoperation.
operation/call-query:describes how a query is to be invoked with the data received in the operation invocation.
- call-query/@href: an OPTIONAL reference to the query that is to be invoked. If this is missing then a query must be nested within this element.
- call-query/with-param: a description of a parameter binding for the query invocation: says how a named parameter's value is computed.
  - with-param/@name: a REQUIRED NMTOKEN identifying the parameter whose value is being specified.
  - with-param/@query-param: an OPTIONAL attribute indicating the name of the URI query parameter (from operation/@path) whose value is the value of this parameter.
  - with-param/@column: an OPTIONAL attribute naming a column of the immediate parent <result> element. That is, this applies onlyfornested queries and serves the purpose of being able to use a query result as input to a nested query.
  - with-param/@param: an OPTIONAL attribute naming a <param> of the parent <query>. That is, this applies onlyfornested queries and serves the purpose of being able to use a parameter of the parent query input to a nested query.
- call-query/query: an OPTIONAL <query> being the anonymous query to be invoked as the implementation of this operation with the parameters identified above.

Defining resources

<resource path="uri-template" method="GET|POST|PUT|DELETE" disableStreaming="xs:BOOLEAN">
    <description>"xs:string"</description>
    <call-query href="xs:IDREF"      />
        <with-param name="xs:NMTOKEN" />
        query?
    </call-query>
</resource>

This defines the resource identified by "new URI (/data/@baseURI, /data/resource/@path)" and indicates how the request is mapped to a query invocation.

Defining event trigger

<event-trigger id=xs:NCName" language="XPath">
     <expression>xs:string</expression>
     <target-topic>xs:string</target-topic>
     <subscriptions>
         <subscription>xs:string</subscription>
     </subscriptions>
</event-trigger>

event-triger/@id: REQUIRED id used to identify the event-trigger, used in data services queries.
event-triger/language REQUIRED currently only XPath issupported asthe event trigger language.
target-topic REQUIRED topic, to which the event notifications will be published.
subscriptions REQUIRED can be any WS-Eventingcomplientendpoint. For example, an SMTP transport can be used to send a message to a mail inbox, where an email address is given as the subscription. Here many subscriptions can be defined for the given topic.

Security configuration

When a data service receives messages, it expects to receive a signed and encrypted message as specified by the security policy stored in the registry of your server. Therefore, as shown below, you can embed the security configurations directly in the .dbs file of the data service by adding the path to the relevant security policy. Please see Apache Rampart and Axis2 documentation on the format of the policy file stored in the registry. You can also use the 'enableSec' element to ensure that Apache Rampart is engaged for the data service.

<policy key="<sec_policy_path>"/>
<enableSec/>

Sample data service configuration

Given below is a sample data service configuration with queries, resources etc. for your reference:

<data name="DSSample" enableBatchRequests="false" enableBoxcarring="true" serviceStatus="active" baseURI="http://ws.wso2.org/dataservice/samples/ds_sample" transports="http https JMS local">
   <config id="default">
      <property name="org.wso2.ws.dataservice.driver">org.h2.Driver</property>
      <property name="org.wso2.ws.dataservice.protocol">jdbc:h2:file:./samples/database/DATA_SERV_SAMP</property>
      <property name="org.wso2.ws.dataservice.user">wso2ds</property>
      <property name="org.wso2.ws.dataservice.password">wso2ds</property>
      <property name="org.wso2.ws.dataservice.minpoolsize">1</property>
      <property name="org.wso2.ws.dataservice.maxpoolsize">10</property>
      <property name="org.wso2.ws.dataservice.validation_query"></property>
   </config>
    <query id="employeesByNumberSQL" useConfig="default">
      <sql>select * from Employees where employeeNumber = ?</sql>
      <result element="employees" rowName="employee">
         <element name="last-name" column="lastName" />
         <element name="first-name" column="firstName" />
         <element name="email" column="email" />
         <element name="salary" column="salary" />
      </result>
       <param name="employeeNumber" paramType="SCALAR" sqlType="INTEGER" type="IN" ordinal="1" >
          <validateLength minimum="3" maximum="20" />
       </param>
   </query>
  <query id="updateProductQuantityQuery" useConfig="default" input-event-trigger="product_stock_low_trigger">
      <sql>update Products set quantityInStock=? where productCode=?</sql>
      <param name="productCode" paramType="SCALAR" sqlType="STRING" type="IN" ordinal="2" />
      <param name="quantityInStock" paramType="SCALAR" sqlType="DOUBLE" type="IN" ordinal="1" />
   </query>
    <query id="createProductQuery" useConfig="default">
      <sql>insert into Products (productCode, productName, productLine, quantityInStock, buyPrice) values (?,?,?,?,?)</sql>
      <param name="productCode" paramType="SCALAR" sqlType="STRING" type="IN" ordinal="1" />
      <param name="productName" paramType="SCALAR" sqlType="STRING" type="IN" ordinal="2" />
      <param name="productLine" paramType="SCALAR" sqlType="STRING" type="IN" ordinal="3" />
      <param name="quantityInStock" paramType="SCALAR" sqlType="INTEGER" type="IN" ordinal="4" />
      <param name="buyPrice" paramType="SCALAR" sqlType="DOUBLE" type="IN" ordinal="5" />
   </query>
  <operation name="employeesByNumber">
      <call-query href="employeesByNumberSQL"           >
         <with-param name="employeeNumber" query-param="employeeNumber" />
      </call-query>
   </operation>
   <event-trigger id="product_stock_low_trigger" language="XPath">
      <expression>/updateProductQuantityQuery/quantityInStock&lt;10</expression>
      <target-topic>product_stock_low_topic</target-topic>
      <subscriptions>
         <subscription>mailto:test@test.com</subscription>
      </subscriptions>
   </event-trigger>
    <resource path="product/{productCode}/{productName}/{productLine}/{quantityInStock}/{buyPrice}" method="POST">
      <call-query href="createProductQuery"          >
         <with-param name="productCode" query-param="productCode" />
         <with-param name="productName" query-param="productName" />
         <with-param name="productLine" query-param="productLine" />
         <with-param name="quantityInStock" query-param="quantityInStock" />
         <with-param name="buyPrice" query-param="buyPrice" />
      </call-query>
   </resource>
   <policy key="conf:repository/components/org.wso2.carbon.security.mgt/policy/scenario1"/>
   <enableSec/>
</data>