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.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency> 
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-sql</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

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

From Camel 2.11 onwards this component can create both consumer (e.g. from()) and producer endpoints (e.g. to()).

In previous versions, it could only act as a producer.

This component can be used as a Transactional Client.

The SQL component uses the following endpoint URI notation:

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

From Camel 2.11 onwards you can use named parameters by using :#name_of_the_parameter style as shown:

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

When using named parameters, Camel will lookup the names from, in the given precedence:
1. from message body if its a java.util.Map
2. from message headers

If a named parameter cannot be resolved, then an exception is thrown.

From Camel 2.14 onward you can use Simple expressions as parameters as shown:

sql:select * from table where id=:#${property.myId} 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.

From Camel 2.17 onwards you can externalize your SQL queries to files in the classpath or file system as shown:

sql:classpath:sql/myquery.sql[?options]

And the myquery.sql file is in the classpath and is just a plain text

select * from table where id = :#${property.myId} order by name 

In the file you can use multilines and format the SQL as you wish. And also use comments such as the – dash line.

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

Options

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 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.

From Camel 2.16 onwards you can use the option useMessageBodyForSql that allows to use the message body as the SQL statement, and then the SQL parameters must be provided in a header with the key SqlConstants.SQL_PARAMETERS. This allows the SQL component to work more dynamic as the SQL query is from the message body.

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.

By default, the result is placed in the message body.  If the outputHeader parameter is set, the result is placed in the header.  This is an alternative to using a full message enrichment pattern to add headers, it provides a concise syntax for querying a sequence or some other small value into a header.  It is convenient to use outputHeader and outputType together:

from("jms:order.inbox")
    .to("sql:select order_seq.nextval from dual?outputHeader=OrderId&outputType=SelectOne")
    .to("jms:order.booking");

Using StreamList

From Camel 2.18 onwards the producer supports outputType=StreamList that uses an iterator to stream the output of the query. This allows to process the data in a streaming fashion which for example can be used by the Splitter EIP to process each row one at a time, and load data from the database as needed.

from("direct:withSplitModel")
   .to("sql:select * from projects order by id?outputType=StreamList&outputClass=org.apache.camel.component.sql.ProjectModel")
   .to("log:stream")
   .split(body()).streaming()
       .to("log:row")
       .to("mock:result")
   .end();

Header values

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

When performing insert operations, the SQL Component stores the rows with the generated keys and number of these rown in the following message headers (Available as of Camel 2.12.4, 2.13.1):

CamelSqlGeneratedKeysRowCount

CamelSqlGeneratedKeyRows

Generated keys

Available as of Camel 2.12.4, 2.13.1 and 2.14

If you insert data using SQL INSERT, then the RDBMS may support auto generated keys. You can instruct the SQL producer to return the generated keys in headers.
To do that set the header CamelSqlRetrieveGeneratedKeys=true. Then the generated keys will be provided as headers with the keys listed in the table above.

You can see more details in this unit test.

Configuration

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

 select * from table where id=# order by name?dataSource=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 in java:

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?dataSource=#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 named parameters

Available as of Camel 2.11

In the given route below, we want to get all the projects from the projects table. Notice the SQL query has 2 named parameters, :#lic and :#min.
Camel will then lookup for these parameters from the message body or message headers. Notice in the example above we set two headers with constant value
for the named parameters:

from("direct:projects")
   .setHeader("lic", constant("ASF"))
   .setHeader("min", constant(123))
   .to("sql:select * from projects where license = :#lic and id > :#min order by id")

Though if the message body is a java.util.Map then the named parameters will be taken from the body.

from("direct:projects") 
   .to("sql:select * from projects where license = :#lic and id > :#min order by id")

Using expression parameters

Available as of Camel 2.14

In the given route below, we want to get all the project from the database. It uses the body of the exchange for defining the license and uses the value of a property as the second parameter.

from("direct:projects")
   .setBody(constant("ASF"))
   .setProperty("min", constant(123)) 
   .to("sql:select * from projects where license = :#${body} and id > :#${property.min} order by id")

Using IN queries with dynamic values

Available as of Camel 2.17

From Camel 2.17 onwards the SQL producer allows to use SQL queries with IN statements where the IN values is dynamic computed. For example from the message body or a header etc.

To use IN you need to:

• prefix the parameter name with in:
• add ( ) around the parameter

An example explains this better. The following query is used:

select * from projects where project in (:#in:names) order by id 

In the following route:

from("direct:query") 
  .to("sql:classpath:sql/selectProjectsIn.sql") 
  .to("log:query") 
  .to("mock:query");

Then the IN query can use a header with the key names with the dynamic values such as:

// use an array 
template.requestBodyAndHeader("direct:query", "Hi there!", "names", new String[]{"Camel", "AMQ"});
 
// use a list 
List<String> names = new ArrayList<String>();
names.add("Camel"); 
names.add("AMQ");
template.requestBodyAndHeader("direct:query", "Hi there!", "names", names);
 
// use a string separated values with comma 
template.requestBodyAndHeader("direct:query", "Hi there!", "names", "Camel,AMQ");

The query can also be specified in the endpoint instead of being externalized (notice that externalizing makes maintaining the SQL queries easier)

from("direct:query") 
  .to("sql:select * from projects where project in (:#in:names) order by id") 
  .to("log:query") 
  .to("mock:query");

Using the JDBC based idempotent repository

Available as of Camel 2.7: 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. For Camel 2.7, we use the following schema:

 sqlCREATE TABLE CAMEL_MESSAGEPROCESSED (
   processorName VARCHAR(255),
   messageId VARCHAR(100) ) 

In Camel 2.8, we added the createdAt column:

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

 The SQL Server TIMESTAMP type is a fixed-length binary-string type. It does not map to any of the JDBC time types: DATE, TIME, or 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> 

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:

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:

Optimistic Locking

Optimistic locking is set to on by default.  If two exchanges attempt to insert at the same time an exception will thrown, caught, converted to an OptimisticLockingException, and rethrown.  

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.

From Camel 2.11 onwards you can store the message body and select(ed) headers as String in separate columns.

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:

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) 
);

Storing body and headers as text

Available as of Camel 2.11

You can configure the JdbcAggregationRepository to store message body and select(ed) headers as String in separate columns. For example to store the body, and the following two headers companyName and accountName use the following SQL:

CREATE TABLE aggregationRepo3 (
 id varchar(255) NOT NULL, 
 exchange blob NOT NULL, 
 body varchar(1000),
 companyName varchar(1000),
 accountName varchar(1000),
 constraint aggregationRepo3_pk PRIMARY KEY (id) 
);
 
CREATE TABLE aggregationRepo3_completed (
 id varchar(255) NOT NULL,
 exchange blob NOT NULL,
 body varchar(1000),
 companyName varchar(1000),
 accountName varchar(1000),
 constraint aggregationRepo3_completed_pk PRIMARY KEY (id) 
); 

And then configure the repository to enable this behavior as shown below:

<bean id="repo3" class="org.apache.camel.processor.aggregate.jdbc.JdbcAggregationRepository">
    <property name="repositoryName" value="aggregationRepo3"/>
    <property name="transactionManager" ref="txManager3"/>
    <property name="dataSource" ref="dataSource3"/>
    <!-- configure to store the message body and following headers as text in the repo -->
    <property name="storeBodyAsText" value="true"/>
    <property name="headersToStoreAsText">
       <list>
           <value>companyName</value>
           <value>accountName</value>
       </list>
    </property>
 </bean>

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>

Optimistic locking

From Camel 2.12 onwards you can turn on optimisticLocking and use this JDBC based aggregation repository in a clustered environment where multiple Camel applications shared the same database for the aggregation repository. If there is a race condition there JDBC driver will throw a vendor specific exception which the JdbcAggregationRepository can react upon. To know which caused exceptions from the JDBC driver is regarded as an optimistick locking error we need a mapper to do this. Therefore there is a org.apache.camel.processor.aggregate.jdbc.JdbcOptimisticLockingExceptionMapper allows you to implement your custom logic if needed. There is a default implementation org.apache.camel.processor.aggregate.jdbc.DefaultJdbcOptimisticLockingExceptionMapper which works as follows:

The following check is done:

If the caused exception is an SQLException then the SQLState is checked if starts with 23.

If the caused exception is a DataIntegrityViolationException

If the caused exception class name has "ConstraintViolation" in its name.

optional checking for FQN class name matches if any class names has been configured

You can in addition add FQN classnames, and if any of the caused exception (or any nested) equals any of the FQN class names, then its an optimistick locking error.

Here is an example, where we define 2 extra FQN class names from the JDBC vendor.

<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"/>
   <property name"jdbcOptimisticLockingExceptionMapper" ref="myExceptionMapper"/>
</bean> 
<!-- use the default mapper with extra FQN class names from our JDBC driver --> 
<bean id="myExceptionMapper" class="org.apache.camel.processor.aggregate.jdbc.DefaultJdbcOptimisticLockingExceptionMapper">
   <property name="classNames"> 
     <util:set> 
       <value>com.foo.sql.MyViolationExceptoion</value>
       <value>com.foo.sql.MyOtherViolationExceptoion</value>
     </util:set>
   </property>
</bean> 

See Also

Endpoint 

SQL Stored Procedure

JDBC