# 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.

## 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

Table 71. URI options

Option | Type | Default | Description
--- | --- | --- | ---
`batch` | `boolean` | `false` | Apache Camel 2..7.5/2.8.4/2.9: Specifies whether to execute SQL batch update statements. When set to `true`, the SQL component expects an iterator that contains the parameter iterators, instead of an iterator of parameters. The size of the outer iterator determines batch size.
`dataSourceRef` | `String` | `null` | Apache Camel 1.5.1/2.0: Reference to a `DataSource` to look up in the registry.
`placeholder` | `String` | `#` | Apache 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.

## 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:

Table 72. Message headers

Header | Description
--- | ---
`SqlProducer.UPDATE_COUNT` | Apache Camel 1.x: The number of rows updated for `update` operations, returned as an `Integer` object.
`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.

## Configuration in Apache Camel 1.5.0 or lower

The SQL component must be configured before it can be used. In Spring, you can configure it as follows:

    <bean id="sql" class="org.apache.camel.component.sql.SqlComponent">
        <property name="dataSource" ref="myDS"/>
    </bean>

    <bean id="myDS" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/ds" />
        <property name="username" value="username" />
        <property name="password" value="password" />
    </bean>

## Configuration in Apache Camel 1.5.1 or higher

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
    jdbcTemplate.execute("create table projects (id integer primary key,"
                         + "project varchar(10), license varchar(5))");
    jdbcTemplate.execute("insert into projects values (1, 'Camel', 'ASF')");
    jdbcTemplate.execute("insert into projects values (2, 'AMQ', 'ASF')");
    jdbcTemplate.execute("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

Available as of Apache Camel 2.7: In this section we will use the JDBC based idempotent repository.

First we need to setup a `javax.sql.DataSource` in the Spring XML file:

    <bean id="dataSource" class="org.springframework.jdbc.datasource.SingleConnectionDataSource">
        <property name="driverClassName" value="org.hsqldb.jdbcDriver"/>
        <property name="url" value="jdbc:hsqldb:mem:camel_jdbc"/>
        <property name="username" value="sa"/>
        <property name="password" value=""/>
    </bean>

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>

## Using the JDBC based aggregation repository

Available as of Apache Camel 2.6

| Important
In Apache Camel 2.6, the JdbcAggregationRepository is provided in the `camel-jdbc-aggregator` component. From Apache 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:

Table 73. jdbcAggregateRepository 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 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 are set when an exchange is being recovered/redelivered:

Table 74. Recovery/redelivery headers

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>

See also:

- JDBC