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:

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

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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.

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This component can be used as a Transactional Client.

The SQL component uses the following endpoint URI notation:

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

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:

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

Deprecated and will be removed in Camel 3.0: Reference to a DataSource to look up in the registry. Use dataSource=#theName instead.

dataSource

String

null

Camel 2.11: 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). This replacement is only happening if the endpoint is created using the SqlComponent. If you manually create the endpoint, then use the expected ? sign instead.

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.

allowNamedParameters

boolean

true

Camel 2.11: Whether to allow using named parameters in the queries.

processingStrategy

 

 

Camel 2.11: SQL consumer only: Allows to plugin to use a custom org.apache.camel.component.sql.SqlProcessingStrategy to execute queries when the consumer has processed the rows/batch.

prepareStatementStrategy

 

 

Camel 2.11: Allows to plugin to use a custom org.apache.camel.component.sql.SqlPrepareStatementStrategy to control preparation of the query and prepared statement.

consumer.delay

long

500

Camel 2.11: SQL consumer only: Delay in milliseconds between each poll.

consumer.initialDelay

long

1000

Camel 2.11: SQL consumer only: Milliseconds before polling starts.

consumer.useFixedDelay

boolean

false

Camel 2.11: SQL consumer only: Set to true to use fixed delay between polls, otherwise fixed rate is used. See ScheduledExecutorService in JDK for details.

maxMessagesPerPoll

int

0

Camel 2.11: SQL consumer only: An integer value to define the maximum number of messages to gather per poll. By default, no maximum is set.

consumer.useIterator

boolean

true

Camel 2.11: SQL consumer only: If true each row returned when polling will be processed individually. If false the entire java.util.List of data is set as the IN body.

consumer.routeEmptyResultSet

boolean

false

Camel 2.11: SQL consumer only: Whether to route a single empty Exchange if there was no data to poll.

consumer.onConsume

String

null

Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange was processed successfully, for example to mark the row as processed. The query can have parameter.

consumer.onConsumeFailed

String

null

Camel 2.11: SQL consumer only: After processing each row then this query can be executed, if the Exchange failed, for example to mark the row as failed. The query can have parameter.

consumer.onConsumeBatchComplete

String

null

Camel 2.11: SQL consumer only: After processing the entire batch, this query can be executed to bulk update rows etc. The query cannot have parameters.

consumer.expectedUpdateCount

int

-1

Camel 2.11: SQL consumer only: If using consumer.onConsume then this option can be used to set an expected number of rows being updated. Typically you may set this to 1 to expect one row to be updated.

consumer.breakBatchOnConsumeFail

boolean

false

Camel 2.11: SQL consumer only: If using consumer.onConsume and it fails, then this option controls whether to break out of the batch or continue processing the next row from the batch.

alwaysPopulateStatement

boolean

false

Camel 2.11: SQL producer only: If enabled then the populateStatement method from org.apache.camel.component.sql.SqlPrepareStatementStrategy is always invoked, also if there is no expected parameters to be prepared. When this is false then the populateStatement is only invoked if there is 1 or more expected parameters to be set; for example this avoids reading the message body/headers for SQL queries with no parameters.

separator

char

,

Camel 2.11.1: The separator to use when parameter values is taken from message body (if the body is a String type), to be inserted at # placeholders. Notice if you use named parameters, then a Map type is used instead.

outputType

String

SelectList

Camel 2.12.0: Make the output of consumer or producer to SelectList as List of Map, or SelectOne as single Java object in the following way:
a) If the query has only single column, then that JDBC Column object is returned. (such as SELECT COUNT( * ) FROM PROJECT will return a Long object.
b) If the query has more than one column, then it will return a Map of that result.
c) If the outputClass is set, then it will convert the query result into an Java bean object by calling all the setters that match the column names. It will assume your class has a default constructor to create instance with.
d) If the query resulted in more than one rows, it throws an non-unique result exception.

outputClass

String

null

Camel 2.12.0: Specify the full package and class name to use as conversion when outputType=SelectOne.

parametersCount

int

0

Camel 2.11.2/2.12.0 If set greater than zero, then Camel will use this count value of parameters to replace instead of querying via JDBC metadata API. This is useful if the JDBC vendor could not return correct parameters count, then user may override instead.

noop

boolean

false

Camel 2.12.0 If set, will ignore the results of the SQL query and use the existing IN message as the OUT message for the continuation of processing

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.

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

The number of rows updated for update operations, returned as an Integer object.

CamelSqlRowCount

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

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):

Header

Description

CamelSqlGeneratedKeysRowCount
The number of rows in the header that contains generated keys.
CamelSqlGeneratedKeyRows
 Rows that contains the generated keys (a list of maps of keys).

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:

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:

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

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.

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

We could configure the DataSource in Spring XML as follows:

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:

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

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.

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

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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:

In Camel 2.8, we added the createdAt column:

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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:

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

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:

Using the JDBC based aggregation repository

Available as of Camel 2.6

Using JdbcAggregationRepository in Camel 2.6

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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.

storeBodyAsText

boolean

Camel 2.11: Whether to store the message body as String which is human readable. By default this option is false storing the body in binary format.

headersToStoreAsText

List<String>

Camel 2.11: Allows to store headers as String which is human readable. By default this option is disabled, storing the headers in binary format.

optimisticLocking

false

Camel 2.12: To turn on optimistic locking, which often would be needed in clustered environments where multiple Camel applications shared the same JDBC based aggregation repository.

jdbcOptimisticLockingExceptionMapper

 

Camel 2.12: Allows to plugin a custom org.apache.camel.processor.aggregate.jdbc.JdbcOptimisticLockingExceptionMapper to map vendor specific error codes to an optimistick locking error, for Camel to perform a retry. This requires optimisticLocking to be enabled.

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:

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.

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:

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

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:

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.

See Also

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