How to read REST service that returns JSON object

So I have a REST based service which is hosted at

http://localhost:35798/RestServiceImpl.svc/json/567

If I query that, I get the result as:

{"JSONDataResult":"You requested product 567"}

I need to store the whole JSON data into a PostgreSQL table:

CREATE TABLE "JsonTable"
(
  "StoreJsonObject" json
)

If I want to parse the value field i.e. "You requested product 567", the program works (here I am using a different table whose column type is text):

<jdbc:postgresql-data-source name="PostgreSQL_Data_Source" user="username" password="pwd" url="jdbc:postgresql://localhost:5432/TestDB" transactionIsolation="UNSPECIFIED" doc:name="PostgreSQL Data Source"/>
<jdbc:connector name="PostgreSQL_Connector" dataSource-ref="PostgreSQL_Data_Source" validateConnections="true" queryTimeout="-1" pollingFrequency="0" doc:name="Database">
    <jdbc:query key="InsertRecord" value="INSERT INTO &quot;AnotherJSonTable&quot;(&quot;StoreJsonObject&quot;) VALUES (#[message.payload])"/>
</jdbc:connector>
<flow name="testRestFlow1" doc:name="testRestFlow1">
    <http:inbound-endpoint exchange-pattern="request-response" address="http://localhost:8082/index.html"  doc:name="HTTP"/>
    <http:rest-service-component httpMethod="GET" serviceUrl="http://localhost:35798/RestServiceImpl.svc/json/567">
    </http:rest-service-component>
    <json:json-to-object-transformer returnClass="java.util.Map" doc:name="JSON to Object"/>
    <expression-transformer expression="#[message.payload.JSONDataResult]" doc:name="Expression"/>
    <jdbc:outbound-endpoint exchange-pattern="one-way" queryKey="InsertRecord" queryTimeout="-1" connector-ref="PostgreSQL_Connector" doc:name="Database"/>
</flow>

But how to store the entire JSON object ({"JSONDataResult":"You requested product 567"}).
What do I need to change in the "expression-transformer"?

If I do:

<jdbc:query key="InsertRecord" value="INSERT INTO &quot;JsonTable&quot;(&quot;StoreJsonObject&quot;) VALUES (#[message.payload])"/>

<expression-transformer expression="#[message.payload]" doc:name="Expression"/>

I receive exception:

Root Exception stack trace:
org.postgresql.util.PSQLException: No hstore extension installed.
    at org.postgresql.jdbc2.AbstractJdbc2Statement.setMap(AbstractJdbc2Statement.java:1713)
    at org.postgresql.jdbc2.AbstractJdbc2Statement.setObject(AbstractJdbc2Statement.java:1916)
    at org.postgresql.jdbc3g.AbstractJdbc3gStatement.setObject(AbstractJdbc3gStatement.java:36)
    + 3 more (set debug level logging or '-Dmule.verbose.exceptions=true' for everything)
********************************************************************************

INFO  2012-12-24 15:48:31,945 [[testrest].connector.file.mule.default.receiver.01] org.mule.transport.file.FileMessageReceiver: Lock obtained on file: C:\Users\niladri.biswas\Desktop\input\all_winjs_ui_controls.txt
INFO  2012-12-24 15:48:31,945 [[testrest].testRestFlow1.stage1.02] org.mule.transport.http.components.RestServiceWrapper: Invoking REST service: http://localhost:35798/RestServiceImpl.svc/json/567
ERROR 2012-12-24 15:48:31,992 [[testrest].PostgreSQL_Connector.dispatcher.01] org.mule.exception.DefaultMessagingExceptionStrategy: 
********************************************************************************
Message               : Failed to route event via endpoint: DefaultOutboundEndpoint{endpointUri=jdbc://InsertRecord, connector=JdbcConnector
{
  name=PostgreSQL_Connector
  lifecycle=start
  this=15e7ea6
  numberOfConcurrentTransactedReceivers=4
  createMultipleTransactedReceivers=false
  connected=true
  supportedProtocols=[jdbc]
  serviceOverrides=<none>
}
,  name='endpoint.jdbc.InsertRecord', mep=ONE_WAY, properties={queryTimeout=-1}, transactionConfig=Transaction{factory=null, action=INDIFFERENT, timeout=0}, deleteUnacceptedMessages=false, initialState=started, responseTimeout=10000, endpointEncoding=UTF-8, disableTransportTransformer=false}. Message payload is of type: LinkedHashMap
Code                  : MULE_ERROR--2
--------------------------------------------------------------------------------

Also the record should be inserted only once after reading from the service and not multiple times.

Since you want to store the whole JSON, there is no need to deserialize it as an object: I suggest you simply transform the HTTP-streamed payload into a java.lang.String and insert it as-is in the DB.

This would done like that:

<jdbc:postgresql-data-source name="PostgreSQL_Data_Source"
    user="username" password="pwd" url="jdbc:postgresql://localhost:5432/TestDB"
    transactionIsolation="UNSPECIFIED" doc:name="PostgreSQL Data Source" />

<jdbc:connector name="PostgreSQL_Connector" dataSource-ref="PostgreSQL_Data_Source"
    validateConnections="true" queryTimeout="-1" pollingFrequency="0"
    doc:name="Database">
    <jdbc:query key="InsertRecord"
        value="INSERT INTO &quot;AnotherJSonTable&quot;(&quot;StoreJsonObject&quot;) VALUES (CAST(#[message.payload] AS json))" />
</jdbc:connector>

<flow name="testRestFlow1" doc:name="testRestFlow1">
    <http:inbound-endpoint exchange-pattern="request-response"
        address="http://localhost:8082/index.html" doc:name="HTTP" />
    <http:rest-service-component httpMethod="GET"
        serviceUrl="http://localhost:35798/RestServiceImpl.svc/json/567" />
    <object-to-string-transformer />
    <jdbc:outbound-endpoint exchange-pattern="one-way"
        queryKey="InsertRecord" queryTimeout="-1" connector-ref="PostgreSQL_Connector"
        doc:name="Database" />
</flow>