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Data Services and Resources

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Last updated: Oct 12, 2012Version comment
10 min read

Data Services and Resources provide a convenient mechanism for offering a service-and-resource-interface to some data stored in a relational database.

When providing the service interface, the user 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. When providing a resource interface, the user 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 sections describe the Data Services configuration language and list out the key elements used when composing a data service, such as queries, databases, operations etc along with examples showing the syntax.

Configuration 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. For example,

<data baseURI="xs:anyURI" name="xs:NMTOKEN" enableBatchRequests="xs:BOOLEAN" enableBoxcarring="xs:BOOLEAN"  enableDTP="xs:BOOLEAN" txManagerJNDIName="xs:NMTOKEN" serviceNamespace="xs:anyURI" serviceGroup="xs:NMTOKEN" serviceStatus="active|inactive" >
    config+
    query+
    operation+
    resource+
    event-trigger+
</data>
  • data/@baseURI: a REQUIRED URI indicating the base URI for the operations and resources defined within the <data> element.
  • data/@name: a REQUIRED name of the data service.
  • data/@enableBatchRequest: an OPTIONAL boolean to enable the batch request feature.
  • data/@enableBoxcarring: an OPTIONAL boolean to enable the boxcarring feature.
  • data/@enableDTP: an OPTIONAL boolean to enable the distributed transaction feature.
  • data/@txManagerJNDIName: an OPTIONAL JNDI name  for overwrite standard JNDI.
  • data/@serviceNamespace: an OPTIONAL URI to uniquely identify the web service.
  • data/@serviceGroup: an OPTIONAL name that used to categorize data-services in different groups.
  • data/@serviceStatus an OPTIONAL string to enable WIP (specifies weather the data service is deployed or work in progress) support.

Configuring the Database

config refers to configuration information about how to connect to the database:

<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 is parametrized and describes 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's 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 syntax of a <query> element is given below:

<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>
  • query/@ID: an OPTIONAL XML ID identifying the query. If <query> is a direct child of <data> then this attribute is required.
  • query/@useConfig: a REQUIRED reference to the datasource that is to be used for query.
  • query/@returnGeneratedKeys: an OPATIONAL boolean to use when need to enable returnGeneratedKeys. When this is set to true then it will add the generated keys to result set.
  • query/param: a declaration of a parameter of the query
    • param/@name: a REQUIRED name of the parameter.
    • param/@sqlType: an OPTIONAL string containing a legal SQL type which defines the type of the parameter. If none is specified then defaults to string.
    • param/@paramType: a REQUIRED parameter type. If none is specified then defaults to SCALAR.
    • param/@ordinal: a  REQUIRED only for stored procedures which map the parameter positions with the query.
    • param/@defaultValue: an OPTIONAL default value of the input parameter.
    • param/validateCustom/@class: a REQUIRED custom validation class to validate the input parameter.
    • param/validateLength/@minimum: a REQUIRED integer when specifying the minimum length of the parameter.
    • param/validateLength/@maximum: a REQUIRED integer when specifying the maximum length of the parameter.
    • param/validatePattern/@pattern: a REQUIRED string pattern to validate the string input parameter.
  • query/sql: a REQUIRED string containing the SQL query to execute.
    • sql/@dialect: an OPTIONAL string containing jdbc driver prefix when need to use sql-dialects.
  • query/sparql: a REQUIRED string containing the sparql query to execute when using RDF as datasource.
  • query/properties: an OPTIONAL XML to define advanced query properties. Each property is defined as a child element of this.
    • property/@name: a REQUIRED name of the property.
  • query/result: a REQUIRED element descriibing how 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.
    • result/@element: a REQUIRED QName which is the name of the element which will hold the results.
    • result/@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.
    • result/@defaultNamespace: an OPTIONAL URI being the default namespace to use for the namespace name of elements and attributes that result columns are mapped to. Defaults to "" (meaning no namespace).
    • result/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.
    • result/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. By default it 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 with boxcarring support.
      • 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]
    • result/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. By default it 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 with boxcarring support.
      • 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]
    • result/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 describe operation.
  • 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 only for nested 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 only for nested 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 is supported  as the event trigger language.
  • target-topic REQUIRED topic, to which the event notifications will be published.
  • subscriptions REQUIRED  can be any WS-Eventing complient endpoint. 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.

Sample Data Service Configuration

Database configuration:

<data name="DSSample" enableBatchRequests="false" enableBoxcarring="true" serviceStatus="active" baseURI="http://ws.wso2.org/dataservice/samples/ds_sample">
   <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>
</data>
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