Chapter 97. SQL Component

SQL Component

The sql: component allows you to work with databases using JDBC queries. The difference between this component and JDBC component is that in case of SQL the query is a property of the endpoint and it uses message payload as parameters passed to the query.

This component uses spring-jdbc behind the scenes for the actual SQL handling.

The SQL component also supports:

a JDBC based repository for the Idempotent Consumer EIP pattern. See further below.
a JDBC based repository for the Aggregator EIP pattern. See further below.

Important

This component can be used as a Transactional Client.

URI format

Warning

The SQL component can only be used to define producer endpoints. In other words, you cannot define an SQL endpoint in a from() statement.

The SQL component uses the following endpoint URI notation:

sql:select * from table where id=# order by name[?options]

Notice that the standard ? symbol that denotes the parameters to an SQL query is substituted with the # symbol, because the ? symbol is used to specify options for the endpoint. The ? symbol replacement can be configured on endpoint basis.

You can append query options to the URI in the following format, ?option=value&option=value&...

Options

Option	Type	Default	Description
`batch`	`boolean`	`false`	Camel 2.7.5, 2.8.4 and 2.9: Execute SQL batch update statements. See notes below on how the treatment of the inbound message body changes if this is set to `true`.
`dataSourceRef`	`String`	`null`	Apache Camel 1.5.1/2.0: Reference to a `DataSource` to look up in the registry.
`placeholder`	`String`	`#`	Camel 2.4: Specifies a character that will be replaced to `?` in SQL query. Notice, that it is simple `String.replaceAll()` operation and no SQL parsing is involved (quoted strings will also change)
`template.<xxx>`		`null`	Sets additional options on the Spring `JdbcTemplate` that is used behind the scenes to execute the queries. For instance, `template.maxRows=10`. For detailed documentation, see the JdbcTemplate javadoc documentation.

Treatment of the message body

The SQL component tries to convert the message body to an object of java.util.Iterator type and then uses this iterator to fill the query parameters (where each query parameter is represented by a # symbol, or other configured placeholder, in the endpoint URI). If the message body is not an array or collection, the conversion results in an iterator that iterates over only one object, which is the body itself.

For example, if the message body is an instance of java.util.List, the first item in the list is substituted into the first occurrence of # in the SQL query, the second item in the list is substituted into the second occurrence of #, and so on.

If batch is set to true, then the interpretation of the inbound message body changes slightly - instead of an iterator of parameters, the component expects an iterator that contains the parameter iterators; the size of the outer iterator determines the batch size.

Result of the query

For select operations, the result is an instance of List<Map<String, Object>> type, as returned by the JdbcTemplate.queryForList() method. For update operations, the result is the number of updated rows, returned as an Integer.

Header values

When performing update operations, the SQL Component stores the update count in the following message headers:

Header	Description
`CamelSqlUpdateCount`	Apache Camel 2.0: The number of rows updated for `update` operations, returned as an `Integer` object.
`CamelSqlRowCount`	Apache Camel 2.0: The number of rows returned for `select` operations, returned as an `Integer` object.
`CamelSqlQuery`	Camel 2.8: Query to execute. This query takes precedence over the query specified in the endpoint URI. Note that query parameters in the header are represented by a `?` instead of a `#` symbol

Configuration

You can now set a reference to a DataSource in the URI directly:

sql:select * from table where id=# order by name?dataSourceRef=myDS

Sample

In the sample below we execute a query and retrieve the result as a List of rows, where each row is a Map<String, Object and the key is the column name.

First, we set up a table to use for our sample. As this is based on an unit test, we do it java code:

// this is the database we create with some initial data for our unit test
db = new EmbeddedDatabaseBuilder()
    .setType(EmbeddedDatabaseType.DERBY).addScript("sql/createAndPopulateDatabase.sql").build();

The SQL script createAndPopulateDatabase.sql we execute looks like as described below:

create table projects (id integer primary key, project varchar(10), license varchar(5));
insert into projects values (1, 'Camel', 'ASF');
insert into projects values (2, 'AMQ', 'ASF');
insert into projects values (3, 'Linux', 'XXX');

Then we configure our route and our sql component. Notice that we use a direct endpoint in front of the sql endpoint. This allows us to send an exchange to the direct endpoint with the URI, direct:simple, which is much easier for the client to use than the long sql: URI. Note that the DataSource is looked up up in the registry, so we can use standard Spring XML to configure our DataSource.

from("direct:simple")
    .to("sql:select * from projects where license = # order by id?dataSourceRef=jdbc/myDataSource")
    .to("mock:result");

And then we fire the message into the direct endpoint that will route it to our sql component that queries the database.

MockEndpoint mock = getMockEndpoint("mock:result");
mock.expectedMessageCount(1);

// send the query to direct that will route it to the sql where we will execute the query
// and bind the parameters with the data from the body. The body only contains one value
// in this case (XXX) but if we should use multi values then the body will be iterated
// so we could supply a List<String> instead containing each binding value.
template.sendBody("direct:simple", "XXX");

mock.assertIsSatisfied();

// the result is a List
List<?> received = assertIsInstanceOf(List.class, mock.getReceivedExchanges().get(0).getIn().getBody());

// and each row in the list is a Map
Map<?, ?> row = assertIsInstanceOf(Map.class, received.get(0));

// and we should be able the get the project from the map that should be Linux
assertEquals("Linux", row.get("PROJECT"));

We could configure the DataSource in Spring XML as follows:

 <jee:jndi-lookup id="myDS" jndi-name="jdbc/myDataSource"/>

Using the JDBC based idempotent repository

In this section we will use the JDBC based idempotent repository.

Abstract class

From Camel 2.9 onwards there is an abstract class org.apache.camel.processor.idempotent.jdbc.AbstractJdbcMessageIdRepository you can extend to build custom JDBC idempotent repository.

First we have to create the database table which will be used by the idempotent repository.

In Camel 2.8, we added the createdAt column:

 CREATE TABLE CAMEL_MESSAGEPROCESSED (
   processorName VARCHAR(255),
   messageId VARCHAR(100),
   createdAt TIMESTAMP
 )

We recommend to have a unique constraint on the columns processorName and messageId. Because the syntax for this constraint differs for database to database, we do not show it here.

Second we need to setup a javax.sql.DataSource in the spring XML file:

<jdbc:embedded-database id="dataSource" type="DERBY" />

And finally we can create our JDBC idempotent repository in the spring XML file as well:

<bean id="messageIdRepository" class="org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository">
	<constructor-arg ref="dataSource" />
	<constructor-arg value="myProcessorName" />
</bean>

<camel:camelContext>
	<camel:errorHandler id="deadLetterChannel" type="DeadLetterChannel" deadLetterUri="mock:error">
		<camel:redeliveryPolicy maximumRedeliveries="0" maximumRedeliveryDelay="0" logStackTrace="false" />
	</camel:errorHandler>
	
	<camel:route id="JdbcMessageIdRepositoryTest" errorHandlerRef="deadLetterChannel">
		<camel:from uri="direct:start" />
		<camel:idempotentConsumer messageIdRepositoryRef="messageIdRepository">
			<camel:header>messageId</camel:header>
			<camel:to uri="mock:result" />
		</camel:idempotentConsumer>
	</camel:route>
</camel:camelContext>

Customize the JdbcMessageIdRepository

Starting with Camel 2.9.1 you have a few options to tune the org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository for your needs:

Parameter	Default Value	Description
createTableIfNotExists	true	Defines whether or not Camel should try to create the table if it doesn't exist.
tableExistsString	SELECT 1 FROM CAMEL_MESSAGEPROCESSED WHERE 1 = 0	This query is used to figure out whether the table already exists or not. It must throw an exception to indicate the table doesn't exist.
createString	CREATE TABLE CAMEL_MESSAGEPROCESSED (processorName VARCHAR(255), messageId VARCHAR(100), createdAt TIMESTAMP)	The statement which is used to create the table.
queryString	SELECT COUNT\(*\) FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?	The query which is used to figure out whether the message already exists in the repository (the result is not equals to '0'). It takes two parameters. This first one is the processor name (`String`) and the second one is the message id (`String`).
insertString	INSERT INTO CAMEL_MESSAGEPROCESSED (processorName, messageId, createdAt) VALUES (?, ?, ?)	The statement which is used to add the entry into the table. It takes three parameter. The first one is the processor name (`String`), the second one is the message id (`String`) and the third one is the timestamp (`java.sql.Timestamp`) when this entry was added to the repository.
deleteString	DELETE FROM CAMEL_MESSAGEPROCESSED WHERE processorName = ? AND messageId = ?	The statement which is used to delete the entry from the database. It takes two parameter. This first one is the processor name (`String`) and the second one is the message id (`String`).

A customized org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository could look like:

<bean id="messageIdRepository" class="org.apache.camel.processor.idempotent.jdbc.JdbcMessageIdRepository">
	<constructor-arg ref="dataSource" />
	<constructor-arg value="myProcessorName" />
	<property name="tableExistsString" value="SELECT 1 FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE 1 = 0" />
	<property name="createString" value="CREATE TABLE CUSTOMIZED_MESSAGE_REPOSITORY (processorName VARCHAR(255), messageId VARCHAR(100), createdAt TIMESTAMP)" />
	<property name="queryString" value="SELECT COUNT(*) FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE processorName = ? AND messageId = ?" />
	<property name="insertString" value="INSERT INTO CUSTOMIZED_MESSAGE_REPOSITORY (processorName, messageId, createdAt) VALUES (?, ?, ?)" />
	<property name="deleteString" value="DELETE FROM CUSTOMIZED_MESSAGE_REPOSITORY WHERE processorName = ? AND messageId = ?" />
</bean>

Using the JDBC based aggregation repository

Available as of Camel 2.6

Using JdbcAggregationRepository in Camel 2.6

In Camel 2.6, the JdbcAggregationRepository is provided in the camel-jdbc-aggregator component. From Camel 2.7 onwards, the JdbcAggregationRepository is provided in the camel-sql component.

JdbcAggregationRepository is an AggregationRepository which on the fly persists the aggregated messages. This ensures that you will not loose messages, as the default aggregator will use an in memory only AggregationRepository. The JdbcAggregationRepository allows together with Camel to provide persistent support for the Aggregator.

It has the following options:

Option	Type	Description
`dataSource`	`DataSource`	Mandatory: The `javax.sql.DataSource` to use for accessing the database.
`repositoryName`	`String`	Mandatory: The name of the repository.
`transactionManager`	`TransactionManager`	Mandatory: The `org.springframework.transaction.PlatformTransactionManager` to mange transactions for the database. The TransactionManager must be able to support databases.
`lobHandler`	`LobHandler`	A `org.springframework.jdbc.support.lob.LobHandler` to handle Lob types in the database. Use this option to use a vendor specific LobHandler, for example when using Oracle.
`returnOldExchange`	boolean	Whether the get operation should return the old existing Exchange if any existed. By default this option is `false` to optimize as we do not need the old exchange when aggregating.
`useRecovery`	boolean	Whether or not recovery is enabled. This option is by default `true`. When enabled the Camel Aggregator automatic recover failed aggregated exchange and have them resubmitted.
`recoveryInterval`	long	If recovery is enabled then a background task is run every x'th time to scan for failed exchanges to recover and resubmit. By default this interval is 5000 millis.
`maximumRedeliveries`	int	Allows you to limit the maximum number of redelivery attempts for a recovered exchange. If enabled then the Exchange will be moved to the dead letter channel if all redelivery attempts failed. By default this option is disabled. If this option is used then the `deadLetterUri` option must also be provided.
`deadLetterUri`	String	An endpoint uri for a Dead Letter Channel where exhausted recovered Exchanges will be moved. If this option is used then the `maximumRedeliveries` option must also be provided.

What is preserved when persisting

JdbcAggregationRepository will only preserve any Serializable compatible data types. If a data type is not such a type its dropped and a WARN is logged. And it only persists the Message body and the Message headers. The Exchange properties are not persisted.

Recovery

The JdbcAggregationRepository will by default recover any failed Exchange. It does this by having a background tasks that scans for failed Exchanges in the persistent store. You can use the checkInterval option to set how often this task runs. The recovery works as transactional which ensures that Camel will try to recover and redeliver the failed Exchange. Any Exchange which was found to be recovered will be restored from the persistent store and resubmitted and send out again.

The following headers is set when an Exchange is being recovered/redelivered:

Header	Type	Description
`Exchange.REDELIVERED`	Boolean	Is set to true to indicate the Exchange is being redelivered.
`Exchange.REDELIVERY_COUNTER`	Integer	The redelivery attempt, starting from 1.

Only when an Exchange has been successfully processed it will be marked as complete which happens when the confirm method is invoked on the AggregationRepository. This means if the same Exchange fails again it will be kept retried until it success.

You can use option maximumRedeliveries to limit the maximum number of redelivery attempts for a given recovered Exchange. You must also set the deadLetterUri option so Camel knows where to send the Exchange when the maximumRedeliveries was hit.

You can see some examples in the unit tests of camel-sql, for example this test.

Database

To be operational, each aggregator uses two table: the aggregation and completed one. By convention the completed has the same name as the aggregation one suffixed with "_COMPLETED". The name must be configured in the Spring bean with the RepositoryName property. In the following example aggregation will be used.

The table structure definition of both table are identical: in both case a String value is used as key (id) whereas a Blob contains the exchange serialized in byte array. However one difference should be remembered: the id field does not have the same content depending on the table. In the aggregation table id holds the correlation Id used by the component to aggregate the messages. In the completed table, id holds the id of the exchange stored in corresponding the blob field.

Here is the SQL query used to create the tables, just replace "aggregation" with your aggregator repository name.

CREATE TABLE aggregation (
    id varchar(255) NOT NULL,
    exchange blob NOT NULL,
    constraint aggregation_pk PRIMARY KEY (id)
);
CREATE TABLE aggregation_completed (
    id varchar(255) NOT NULL,
    exchange blob NOT NULL,
    constraint aggregation_completed_pk PRIMARY KEY (id)
);

Codec (Serialization)

Since they can contain any type of payload, Exchanges are not serializable by design. It is converted into a byte array to be stored in a database BLOB field. All those conversions are handled by the JdbcCodec class. One detail of the code requires your attention: the ClassLoadingAwareObjectInputStream.

The ClassLoadingAwareObjectInputStream has been reused from the Apache ActiveMQ project. It wraps an ObjectInputStream and use it with the ContextClassLoader rather than the currentThread one. The benefit is to be able to load classes exposed by other bundles. This allows the exchange body and headers to have custom types object references.

Transaction

A Spring PlatformTransactionManager is required to orchestrate transaction.

Service (Start/Stop)

The start method verify the connection of the database and the presence of the required tables. If anything is wrong it will fail during starting.

Aggregator configuration

Depending on the targeted environment, the aggregator might need some configuration. As you already know, each aggregator should have its own repository (with the corresponding pair of table created in the database) and a data source. If the default lobHandler is not adapted to your database system, it can be injected with the lobHandler property.

Here is the declaration for Oracle:

    <bean id="lobHandler" class="org.springframework.jdbc.support.lob.OracleLobHandler">
        <property name="nativeJdbcExtractor" ref="nativeJdbcExtractor"/>
    </bean>

    <bean id="nativeJdbcExtractor" class="org.springframework.jdbc.support.nativejdbc.CommonsDbcpNativeJdbcExtractor"/>

    <bean id="repo" class="org.apache.camel.processor.aggregate.jdbc.JdbcAggregationRepository">
        <property name="transactionManager" ref="transactionManager"/>
        <property name="repositoryName" value="aggregation"/>
        <property name="dataSource" ref="dataSource"/>
        <!-- Only with Oracle, else use default -->
        <property name="lobHandler" ref="lobHandler"/>
    </bean>